Chemical Glossary

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A

Absolute alcohol	Common name for high purity ethanol or ethyl alcohol.
Absolute error	Expression of the uncertainty or inaccuracy of a measurement.
Absolute temperature	Temperature measured using the Kelvin scale.
Absolute uncertainty	The uncertainty of a scientific measurement, given in the same units as the measurement.
Absolute zero	- 273.15 °C or 0 K, the temperature where all movement stops even on a molecular level, it is also lowest temperature on the Kelvin scale.
Absorbance	Measure of the amount of light absorbed by a sample.
Absorption spectroscopy	Technique used to determine concentration and structure of a sample based on which wavelengths of light are absorbed.
Absorption spectrum	Graph of amount of absorption as a function of wavelength.
Absorption	The take up of a gas/light by a solid or liquid
Absorptivity	Absorption cross section of extinction coefficient, which is the absorbance of a solution per unit path length and concentration.
Accuracy	The closeness of a measurement to a true or accepted value.
Achiral	Describes any molecule or object that is superimposable upon its mirror image.
Acid anhydride	A nonmetal oxide that reacts with water to form an acidic solution.
Acid dissociation constant	Ka - a quantitative measure of how strong an acid is.
Acid	A chemical species that accepts electrons or donate protons or hydrogen ions.
Acid-base indicator	A weak acid or weak base that changes color when the concentration of hydrogen or hydroxide ions changes in an aqueous solution.
Acid-base titration	A procedure to find the concentration of an acid or base by reacting a known concentration with the unknown until the equivalence point is reached.
Acidic	Describes a solution with a relatively high concentration of H+ ions.
Acidic solution	An aqueous solution with a pH less than 7.0.
Acidification	The process of increasing the hydrogen ion concentration.
Acidity	The quantitative capacity of aqueous solutions to react with hydroxyl ions. It is measured by titration with a standard solution of base to a specified end point.
Actinides	Usually, the actinides are considered to be elements 90 (thorium) through 103 (lawrencium). Otherwise, the actinides are defined according to their common properties.
Actinium	The name for the element with atomic number 89 and is represented by the symbol Ac. It is a member of the actinide group.
Activated complex	An intermediate state at the maximum energy point on the reaction path that occurs as reactants are being converted into product in a chemical reaction.
Activated sludge process	Removes organic matter from sewage by saturating it with air and microbial organisms.
Activation	Treatment of a substance by heat, radiation, or activating reagent to produce a more complete or rapid chemical or physical change.
Activation energy	Ea - the minimum amount of energy needed for a chemical reaction to occur.
Active transport	The movement of molecules or ions from a region of lower concentration to higher concentration; requires energy
Activity series	List of metals ranked in order of decreasing activity, used to predict which metals displace others in aqueous solutions.
Actual yield	The quantity of product experimentally obtained from a chemical reaction.
Acute health effect	The effect caused by initial exposure to a chemical.
Acyl group	A functional group with the formula RCO- , where R is bound to carbon via a single bond.
Additive	Any material added to a base stock to change its properties, characteristics or performance.
Adhesion	The force or attraction that holds two separate objects together.
Adsorption	The surface retention of solid, liquid or gas molecules, atoms or ions by a solid or liquid. The adhesion of an extremely thin layer solid, liquid, or vapor molecules to the surface of a solid or liquid.
Adulterant	A chemical that acts as a contaminant in the context of another substance's purity.
Advanced waste treatment	Any treatment method or process employed following biological treatment (1) to reduce pollution load (2) to remove substances that may be harmful to receiving waters or the environment (3) to produce a high-quality effluent suitable for reuse in any specific manner or for discharge under critical conditions. The term tertiary treatment is commonly used to denote advanced waste treatment methods.
Aerobic	Living or occurring only in the presence of oxygen.
Aerobic biological oxidation	Any waste treatment process or other process utilizing aerobic organisms, in the presence of air or oxygen, as the agent for reducing pollution load, oxygen demand, or the amount of organic substance in waste. The term is used in reference to secondary treatment of wastes.
Aerogel	A porous solid formed by replacing the liquid in a gel with a gas; what remains when the liquid part of an alcogel is removed without damaging the solid part.
Aether	A medium believed to carry light waves in the 18th and 19th century.
Air	The mixture of gases that make up the Earth's atmosphere, consisting mainly of nitrogen, with oxygen, water vapor, argon, and carbon dioxide.
Alchemy	Several definitions of alchemy exist. Originally, alchemy was an ancient tradition of sacred chemistry used to discern the spiritual and temporal nature of reality, its structure, laws, and functions.
alcogel	A gel formed by the coagulation of a sol in which the liquid is alcohol; at the gel point, the mixture forms a rigid substance that can stand on its own. The liquid and solid parts of an alcogel occupy the same volume.
Alcohol	Any class of organic compounds containing the hydroxyl group, OH. Specifically, the term is applied to ethyl alcohol (C2H5OH).
Algaecide	Chemical agent added to water to destroy algae.
Aliphatic amino acid	Amino acid that has an aliphatic side chain.
Aliphatic compound	An organic compound containing carbon and hydrogen joined into straight chains, branches chains, or non-aromatic rings.
Aliphatic hydrocarbon	A hydrocarbon containing carbon and hydrogen joined into straight chains, branches chains, or non-aromatic rings.
Alkali metal	Any element found in group IA (first column) of the periodic table.
Alkaline	Describes an alkali (basic) or a solution that has excess of hydroxide ions.
Alkalinity	The capacity of water to neutralize acids, a property imparted by the water's content of carbonate, bicarbonate, hydroxide, and on occasion borate, silicate, and phosphate. It is expressed in milligrams per liter of equivalent calcium carbonate (mg/l CaCO3).
Alkane	A saturated hydrocarbon with the general formula CnH2n+2.
Alkanolamine	An amine where some or all of the alkyl groups attached to the nitrogen contain hydroxyl functionality. For example; triethanolamine (TEA), monisopropanolamine (MIPA).
Alkene	A hydrocarbon containing a double carbon-carbon bond.
Alkenyl group	The hydrocarbon group formed when a hydrogen atom is removed from an alkene group.
Alkoxide	An organic functional group formed when a hydrogen atom is removed from the hydroxyl group of an alcohol when it is reacted with a metal.
Alkoxy group	Functional group containing an alkyl group bonded to oxygen.
Alkylate	The product of a reaction between an olefin, such as 1-dodecene or Tetramer-M, and an aromatic hydrocarbon, such as benzene, toluene or diphenyl oxide.
Alkylated	A molecule that has attached to it an alkyl group (derived from an alkane - CnH2n+2), which is a saturated hydrocarbon with a single bond available.
Allotrope (allotropic form)	Different bonding arrangements allowing for different forms of matter to be made from a single type of atom. Different forms of matter made in this way are called allotropes. For example, ozone (O3) and dioxygen (O2) are allotropes of the element oxygen. Also, diamond, buckyball, and graphite are allotropes of carbon.
Alloy	A combination of metals usually made to produce a metal with stronger properties of both.
Alpha decay	Spontaneous radioactive decay which produces an alpha particle or helium nucleus.
Alpha particle	Helium nuclei (no electrons) produced in nuclear reactions. They are helium ions, He+2.
Alpha radiation	The ionizing radiation released from radioactive decay emitting an alpha particle.
Alternating current (ac)	Current that reverses its direction at regular intervals, such as a common 115 volt circuit.
Alum	Technically, a double sulfate of ammonium or a univalent or trivalent metal but commonly used to denote aluminum sulfate (Al2(SO4)3.
Amalgam	An alloy of mercury with another metal, often used as a dental filling.
Amide	Functional group containing a carbonyl group linked to a nitrogen atom.
Amine	A class of organic compounds of nitrogen that may be considered as derived from ammonia (NH3) by replacing one or more of the hydrogen atoms by organic radicals, such as CH3 or C6H5, as in methylamine and aniline. The former is a gas at ordinary temperature and pressure, but other amines are liquids or solids. All amines are basic in nature and usually combine readily with hydrochloric or other strong acids to form salts.
Amino acid	An organic acid containing a carboxyl (COOH) and amine (NH2) functional group along with a side chain.
Amorphous	Term describing a solid that does not have crystalline structure.
Amphetamine	Any of the compounds which are substituted or slightly modified amphetamine molecules.
Amphoteric	A compound that can act as a base and an acid.
Amphoteric oxide	Oxide that can act as either an acid or a base in a reaction to produce a salt and water.
Amphoteric surfactant	A surfactant in which the hydrophile has both positive and negative charges. Examples; betaines and amine oxides.
Amphoteric	Substance capable of acting as either an acid or a base.
Anabolism	Metabolic synthesis of proteins, fats and other constituents of living organisms from molecules or simple precursors, which usually requires an input of energy.
Anaerobic	Living or occurring only in the absence of free oxygen.
Anaerobic biological treatment	Any waste treatment process utilizing anaerobic or facultative organisms in the absence of air to reduce the organic matter in water.
Anaerobic waste treatment	(sludge processing) Waste stabilization brought about through the action of microorganisms in the absence of air or elemental oxygen.
Anesthetic	A substance that produces loss of sensation, sometimes with loss of consciousness as well.
Angstrom	A unit of length, used especially in expressing the length of light waves, equal to one ten-thousandth of a micron, or one hundredth-millionth of a centimeter (1 x 10-8 cm).
Angular momentum quantum number	ℓ, the quantum number associated with the angular momentum of an electron.
Anhydrous	A term meaning without water.
Anion	Ion having a negative charge; an atom with extra electrons. Atoms of non-metals, in solution, become anions.
Anionic surfactant	A surfactant in which the hydrophile is negatively charged. Examples; sulfonates and sulfates.
Anode	A positive electrode; the electrode toward which electrons flow; the electrode at which oxidation occurs.
Anthropogenic	Resulting from the actions and influence of human beings.
Antiaromaticity	The unusual instability that results from a continuous cyclic system of 4n pi electrons (where n is any integer).
Antibonding orbital	Molecular orbital with an electron outside the region between the two nuclei.
Antifoam	An additive used to suppress the foaming characteristics of a formulation in service.
Antimatter	Any subatomic particle identical in mass to a proton, neutron, or electron, but with the opposite charge. For example, a positron is a positive electron. A collision between a particle and its respective antiparticle results in both being annihilated, with their masses converted to photons of equivalent energy.
Antimicrobial	A chemical which either destroys or inhibits the growth of microscopic and sub-microscopic organisms.
Anti-periplanar	Periplanar conformation where the dihedral atom between atoms is between 150° and 180°.
Antisense	Having a sequence complementary to a segment of genetic material and serving to inhibit gene function.
Antiwear additive	Compounds which form, or react to form, thin films on highly loaded parts in operation to prevent metal to metal contact, thereby reducing friction at the point of contact.
Aqua regia	Mixture of hydrochloric and nitric acids, capable of dissolving gold, platinum, and palladium.
Aqueous solution	A solution in which water is the solvent.
Aqueous	Describes a system containing water.
Aquifer	Water bearer. Earth materials that contain ground water and through which ground water may flow freely. Some examples of these include sand, porous sandstone, and gravel. Aquifers vary widely in their ability to hold water and the speed at which water flows through them.
Aromatic compound	Mainly an organic molecule that contains a benzene ring.
Aromaticity	The unusual stability that results from a continuous cyclic system of 4n + 2 (where n is any integer) pi-electrons in a cyclic compound. This stability results from complete filling of bonding pi molecular orbitals.
Arrhenius acid	Species that dissociates in water to form protons or hydrogen ions.
Arrhenius base	Species that increases the number of hydroxide ions when added to water.
Aryl	A functional group derived from a simple aromatic ring when one hydrogen is removed from the ring.
Asteroid	Any of the thousands of small bodies that revolve about the sun in orbits lying mostly between those of Mars and Jupiter. Also known as a minor planet.
Asymmetric	Molecules that are not symmetrical.
Atherosclerosis	A disease of the arterial walls characterized by fatty deposits and abnormal tissue growth.
Atmosphere	Unit of pressure equal to 101325 pascals or 760mmHg. Its symbol is atm.
Atom	The smallest unit of an element which has all the properties of the element. It is composed of protons, neutrons and electrons.
Atomic absorption	Quantitative chemical method used for the analysis of elemental constituents.
Atomic mass unit (amu)	A unit of mass equal to 1/12 the mass of the carbon isotope with mass number 12, approximately 1.6604 x 10E-24 gram.
Atomic mass	The average mass of the isotopes of an element. It is the decimal number on the periodic chart. It depends upon both the isotopes' masses and the amount of each isotope present.
Atomic mass/weight	The average weight of an atom of an element, usually expressed relative to one atom of the carbon isotope taken to have a standard weight of 12.
Atomic number	The number of protons in the nucleus of an atom. It is the whole number on the periodic chart. It is also the number of electrons in a neutral atom (where protons = electrons).
Atomic radius	Value used to describe the size of an atom, usually half the distance between two atoms just touching each other.
Atomic solid	Solid in which atoms are bonded to other atoms of the same type.
Atomic volume	Volume occupied by one mole of an element at room temperature.
ATP	ATP is the acronym for the molecule adenosine triphosphate.
Aufbau principle	Idea that electrons are added to orbitals as protons are added to an atom.
Austenite	The face - centered cubic crystalline form of iron.
Autoclave	An airtight chamber use for processes requiring dry temperatures above 212 degrees F.
Autooxidation	Oxidation caused by the atmosphere; an oxidation reaction that is self-catalyzed and spontaneous; an oxidation reaction begun only by an inductor.
Avogadro's Law	Relation that states equal volumes of all gases contain the same number of molecules at the same pressure and temperature.
Avogadro's number	The number of particles present in 1 mole of a substance, experimentally determined to be 6.02 x 1023.
Azeotrope	A solution that retains its chemical composition when distilled.
Azimuthal quantum number	The quantum number associated with the angular momentum of an electron, determining the shape of its orbital.

B

Back titration	Titration in which the analyte concentration is determined by reacting it with a known quantity of excess reagent.
Backflow prevention	A system designed to protect potable water from wastewater contamination which could occur if wastewater pressure exceeds potable water pressure over a cross-connection where one or more check valves fail.
Background radiation	Radiation from external sources, typically from cosmic radiation and radioisotope decay.
Backsiphonage	The backflow of contaminated or polluted water, from a plumbing fixture or cross-connection into a water supply line, due to a lowering of the pressure in the line.
Backwashing	The process of cleaning a rapid sand or mechanical filter by reversing the flow of water.
Bacteria	Any of numerous unicellular microorganisms of the class Schizomycetes, occurring in a wide variety of forms, existing either as free-living organisms or parasites, and having a wide range of biochemical, often pathogenic properties. Some bacteria are capable of causing human, animal or plant diseases; others are essential in pollution control because they break-down organic matter in air and water.
Bacterial examination	The examination of water and wastewater to determine the presence, number, and identification of bacteria. Also called bacterial analysis.
Balance	Any piece of apparatus used to determine the mass of a sample of matter.v. as in balance an equation: to have equal numbers of atoms of each element on the opposite sides of an equation.
Balanced equation	Chemical equation in which the number and type of atoms and the electric charge is the same on both the reactant and product sides of the equation.
Balmer series	The part of the hydrogen emission spectrum for electron transitions n=2 and n>2, There are four lines in the visible spectrum.
Barometer	Instrument used to measure atmospheric pressure.
Base metal	Any metal besides a precious or noble metal used for jewelry or in industry.
Base oil (Naphthenic)	A type of petroleum oil fluid derived from naphthenic crude oil. Contains a high degree of closed ring methylene groups.
Base oil (Paraffinic)	A type of petroleum oil fluid derived from paraffinic crude oil, containing a high proportion of straight chain saturated hydrocarbons.
Base stock	The base carrier fluid, usually a refined petroleum fraction or synthetic fluid, into which additives are blended to produce finished lubricants.
Base	Any substance which contains hydroxyl (OH) groups and furnishes hydroxide ions in solution; a molecular or ionic substance capable of combining with a proton to form a new substance; a substance that provides a pair of electrons for a covalent bond with an acid; a solution with a pH of greater than 7.
Base anhydride	Type of oxide that can form a base if water is added.
Basic solution	Aqueous solution containing more hydroxide ions than hydrogen ions; solution with pH > 7.
Basic	Alkaline or having a pH > 7.
Battery	An electrochemical cell that can be used as a source of direct current at a constant voltage.
Beer's law (Beer-Lambert Law)	Law that states the concentration of a solution is directly proportional to its light absorbance.
Beta decay	Type of radioactive decay that results in spontaneous emission of a beta particle.
Beta particle	An electron or positron emitted during beta decay.
Beta radiation	Ionizing radiation from beta decay in the form of an energetic electron or positron.
Binary acid	An acidic binary compound in which one element is hydrogen and the other element is another nonmetal.
Binary compound	A compound that consists of specifically two elements.
Binding energy	Energy needed to remove an electron from an atom or to separate a proton or neutron from the atomic nucleus.
Bioassay	An assay method using a change in biological activity as a qualitative or quantitative means of analyzing a material response to industrial waste and other wastewater by using viable organisms or live fish as test organisms.
Biochemical oxygen demand (BOD)	The quantity of oxygen used in the biochemical oxidation of organic matter in a specified time, at a specified temperature, and under specified conditions; standard test used in assessing wastewater biological oxygen demand.
Biochemical process	The process by which the life activities of bacteria, and other microorganisms in the search for food, break down complex organic material into simple, more stable substances. Self-purification of sewage, polluted streams, sludge digestion, and all so-called secondary sewage treatments result from this process.
Biochemistry	The science that makes use of chemistry to learn about and explain biologically important systems.
Biocide	Chemical agents with the capacity to kill biological life forms. Bactericides, insecticides, pesticides, etc. are examples.
Biodegradability	The susceptibility of a substance to decomposition by microorganisms; specifically, the rate at which compounds may be chemically broken down by bacteria and/or natural environmental factors.
Biological wastewater treatment	Forms of wastewater treatment in which bacterial or biochemical action is intensified to stabilize, oxidize, and nitrify the unstable organic matter present. Intermittent sand filters, contact beds, trickling filters, and activated sludge processes are examples.
Biomethylation	Becoming methylated through biological action; for example, bacteria can generate methylated mercury in aquatic sediments.
Biomonitoring	The use of living organisms to test the suitability of effluent for discharge into receiving waters and to test the quality of such waters downstream from a discharge.
Bitumen	Natural mixture of polycyclic aromatic hydrocarbons (PAHs).
Black light	A lamp that emits ultraviolet radiation or the invisible radiation emitted by it.
Block copolymer	Copolymer formed by repeating monomer subunits.
Blood alcohol level/content	The amount of alcohol in a person's bloodstream measured in percentages. Abbreviated BAL or BAC.
blowdown	Removal of liquids and/or solids from a process vessel or storage vessel or line by the use of pressure; often used to remove materials which, in high concentrations, could cause damage to the vessel or line, or exceed limits established by best engineering practices.
blowoff	A controlled outlet on a pipeline, tank, or conduit which is used to discharge water or accumulations of material carried by the water.
Bohr's atom	Bohr made significant contributions to the atom. He understood the line spectra-- the reason why only certain wavelengths are emitted when atoms jump down levels.
Boiling point elevation	The increase in a liquid boiling point caused by adding another compound to it.
Boiling point	Temperature at which a liquid's vapor pressure is equal to the external gas pressure.
Boiling	Vigorous phase transition from the liquid to gas state.
Bond	A force which holds together two atoms, two ions, two molecules, or a combination of these.
Bond angle	The angle formed between two adjacent chemical bonds within the same atom.
Bond covalent	The sharing of electrons. There is no rip off because the ionization energies of the atoms are not drastically different in magnitude. The result is neither atom is strong enough to remove the electron from the other atom. (Like two kids of equal strength trying to take a ball away from each other. They both can only hold on to it, neither succeeding in taking it and thus they are bonded).
Bond energy	Quantity of energy needed to break one mole of molecules into component atoms.
Bond enthalpy	Enthalpy change resulting when one mole of bonds in a species are broken at 298 K.
Bond ionic	Formed by electron transfer (the rip off). An element whose electrons are loosely held (first and second columns of chart) surrenders its outer electron(s) to an element with high ionization energy (that therefore has a high electron affinity). The latter are the right hand side of the chart (like the halogens). When the transfer is completed, we have ions produced. The unlike charges of the ions holds them together electrically. Hence, the ionic bond. Elements from opposite sides of the chart have very different ionization energies, so that one atom is strong enough to rip off electrons from the other.
Bond length	The equilibrium distance between atomic nuclei or groups of nuclei that share a chemical bond.
Bond order	A measure of the number of electrons involved in chemical bonds between two atoms in a molecule; usually equal to the number of bonds between the atoms.
Bond-dissociation energy	Energy required to homolytically break a chemical bond.
Boyle's law	Ideal gas law that states the volume of a gas is inversely proportional to its absolute pressure, assuming constant temperature.
Branched chain alkane	An alkane with alkyl groups bonded to the central carbon chain. The molecules are branched, but all C - C bonds are single bonds.
Brass	Brass is defined as an alloy of copper and zinc.
Breakdown	Failure of insulator or insulating medium to prevent discharge or current flow.
Bright stock	A heavy lubricant stock with a low pour point used in finished blends to provide film strength and to reduce the amount of oil consumed.
Brine	Water saturated with salt; a strongly saline solution.
British thermal unit (btu)	The quantity of heat necessary to raise the temperature of 1 pound of water by 1 oF.
Brittleness	The property of matter that is how easily the substance breaks or shatters when force is applied to it.
Bronsted - Lowry acid	Species that yields hydrogen ions.
Bronsted - Lowry base	Species that accepts hydrogen ions in a reaction.
Bronze	Bronze is an alloy of copper, usually containing tin as its main addition.
Buffer solutions	Solutions that resist changes in their pH, even when small amounts of acid or base are added.
Buffer	Either a weak acid and its salt or else a weak base and its salt that form an aqueous solution that can hinder a change in the pH when added to an acid or a base.
Builder	Binds hardness ions, calcium and magnesium, to remove them from solution either as a soluble complex or as a precipitate.
Bulking agent	A fine, solid material which is sometimes added to a wastewater stream to produce clarification or coagulation by adding bulk to the solids.
Bunsen burner	Common laboratory burner that uses natural gas or propane, developed by German chemist Robert Wilhelm Bunsen during the 19th century.

C

Calibration	The checking, adjusting, or systematic standardizing of the graduations of a quantitative measuring instrument.
Calorie	The quantity of heat necessary to raise the temperature of 1 gram of water 1 °C at 1 atmosphere pressure.
Calorimeter	Instrument designed to measure heat flow of a chemical reaction or physical change.
Canal ray tube	Showed that ions are produced by electron bombardment. The simplest positive ion, H+1, is the PROTON.
Capillary action	The spontaneous floe of liquid into a narrow tube or porous material.
Carbocyclic	Being or having an organic ring of carbon atoms.
Carbohydrate	An organic compound with the general formula Cx(H2O)y.
Carbonate	An ion consisting of one carbon bonded to three oxygen atoms (CO32-)or a compound containing this ion.
Carbonyl	Functional group consisting of a carbon atom double bonded to oxygen, C=O.
Carboxyl group	Functional group consisting of a carbon double bonded to oxygen and single bonded to a hydroxyl (-COOH).
Carcinogen	A cancer-causing agent.
Catalysis	A process in which a catalyst increases the speed of a chemical reaction.
Catalyst	A substance that alters the velocity of a chemical reaction and may be recovered essentially unaltered in form and amount at the end of the reaction.
Catenation	Binding of an element to itself via covalent bonds, forming a chain or ring
Cathode	A negative electrode.It is the electrode from which current leaves an electrolytic cell.
Cathode ray tube	A vacuum tube with a source of electrons, a fluorescent screen, and means of accelerating and deflecting the electron beam.
Cation	A positively charged atom or group of atoms, or a radical which moves to the negative pole (cathode) during electrolysis.
Cationic surfactant	Asurfactant in which the hydrophile is positively charged. Examples; quaternary ammonium salts. (see RFF 750.10.01 - SURFACTANTS).
Caustic	Capable of destroying or eating away by chemical action; a hydroxide of a light metal.
Caustic soda	Sodium hydroxide, NaOH.
Celsius temperature scale	Temperature scale where 0°C and 100°C are defined as the freezing and boiling points of water, respectively.
Central atom	In a Lewis structure, usually the atom that is the least electronegative.
Cetane number (CN)	Value that describes the combustion quality of diesel fuel, based on the delay between injection and ignition.
Chain reaction	Set of chemical reactions in which products become reactants of another reaction.
Charge	An electrical charge, a conserved property of subatomic particles determining their electromagnetic interaction.
Charles's law	Ideal gas law that states the volume of an ideal gas is directly proportional to absolute temperature, assuming constant pressure.
Chelate	Organic compound formed by bonding a polydentate ligand to a central metal atom, or the act of forming such a compound.
Chelated	Combined with a metal to form a chelate ring, in which a metal ion is held by coordinate bonds.
Chelation	A process in which a metal ion is coordinatively bound to an organic molecule forming a heterocyclic ring.
Chemical analysis	The use of a standard chemical analytical procedures to determine the concentration of a specific analyte in a sample, or qualitatively or quantitatively measure a specific parameter of a sample.
Chemical bonds	The process by which atoms combine to form molecules.
Chemical change	Process by which one or more substances are altered to form new substances.
Chemical coagulation	The destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of a floc-forming chemical.
Chemical energy	Energy contained in the internal structure of an atom or molecule.
Chemical equation	Description of a chemical reaction, including the reactants, products, and direction of the reaction.
Chemical equilibrium	State of a chemical reaction where the concentration of the reactants and products remains stable over time.
Chemical formula	Expression which states the number and type of atoms in a molecule.
Chemical kinetics	The study of chemical processes and rates of reactions.
Chemical oxygen demand	The amount of oxygen required for the chemical oxidation of organics in a liquid; a chemical test that determines the oxygen equivalent of the amount of organic matter oxidizable by potassium dichromate in a 50% sulfuric acid solution.
Chemical precipitation	(1) The process of utilizing chemicals to produce a separable solid phase within a liquid medium; in analytical chemistry, precipitation is used to separate a solid phase in an aqueous solution. (2) The process of softening water by the addition of lime and soda ash as the precipitants.
Chemical property	Characteristic which may be observed when matter undergoes a chemical change.
Chemical reaction	A chemical change in which reactants form one or more new products.
Chemical symbol	One or two letter representation of a chemical element (e.g., H, Al).
Chemical	Any matter or substance that has mass.
Chemiluminescence	Light emitted as a result of a chemical reaction
Cherenkov radiation	Cherenkov radiation is the electromagnetic radiation emitted when a charged particle moves through a dielectric medium faster than the velocity of light in the medium.
Chiral	Relating to a molecule that cannot be superimposed on its mirror image.
Chiral center	The atom in a molecule bonded to four different chemical species, allowing optical isomerism.
Chirality	Chirality or chiral describes a nonsuperimposable mirror image, like left and right hands. Usually in chemistry the term is used to describe a pair of molecules that have the same formulas, but form a pair of structures.
Chlorination	The addition of chlorine to water or wastewater, generally for the purpose of disinfecting, but frequently done to achieve other biological or chemical results.
Chlorination break point	The addition of chlorine to water, sewage, or industrial waste containing free ammonia to the point where free residual chlorine is available.
Chlorination, free residual	The addition of chlorine to water, sewage or industrial wastes to produce, directly or through the destruction of ammonia or certain organic nitrogenous compounds, a free available chlorine residual.
Chlorine demand	The quantity of chlorine absorbed by wastewater (or water) in a given length of time.
Chlorine, available	The quantity of chlorine released by a bleaching powder when treated with acid.
Chlorine, combined available residual	That portion of the total residual chlorine remaining in water, sewage or industrial waste at the end of a specified contact period, which will react chemically and biologically as chloramines or organic chloramines.
Chlorine, total residual	Free residual chlorine plus combined residual chlorine.
Chlorofluorocarbon	Synthetic compounds containing carbon, chlorine, fluorine, and sometimes hydrogen that are used in refrigerants, propellants, the manufacture of foams, and cleaning solvents.
Chlorophyll	The catalytic substance in photosynthesis that contains a Mg2+ ion inthe center of a specialized ring structure known as a porphyrin.Porphyrins have a central portion containing nitrogen atoms that canattach to a metal ion.
Chromatography	Any process for separating materials using two phases, one stationary, and one moving.One example: gas chromatography (gas as moving phase, solid as stationary phase).
Circuit	A path through which an electrical current can flow when the path is complete.
Clarification	The composite wastewater treatment process consisting of flash mixing of coagulants, pH adjusting chemicals, and/or polyelectrolytes, flocculation, and sedimentation.
Clarifier	A unit which provides for settling and removal of solids from wastewater.
Closed system	Thermodynamic system in which mass is conserved within the system, but energy can freely enter or exit.
Cloud point	Anionics - the temperature at which a product becomes turbid when it is cooled under specific conditions.Nonionics - the temperature at which a product becomes turbid when it is warmed .
Coagulation	The clumping of particles in order to settle out impurities; often induced by chemicals such as lime or alum.
Coenzyme	Substance that works with an enzyme to aid its function or initiate its action.
Cohesion	Measure of how well molecules stick to each other or group together.
Coliform organisms	Any of a number of organisms whose presence in wastewater is an indicator of pollution and of potentially dangerous bacterial contamination.
Colligative properties	Properties of a solution that depend only on the number of particles dissolved in it, not the properties of the particles themselves (e.g. boiling point elevation and freezing point depression).
Colloid	A substance consisting of particles dispersed throughout another substance.
Combination reaction	Reaction in which two reactants combine to form a single product.
Combined gas law	Law which states the ratio of the product of pressure and volume, divided by the absolute temperature, is a constant value.
Combined sewage	A sewage containing both sanitary sewage and surface or storm water with or without industrial wastes.
Combining weight	The apparent equivalent weight of, for example, a sulfonic acid, where two or more acidic components, in this case the sulfonic acid product and sulfuric acid impurity, are present.
Combustible liquid	A liquid which has a flash point above 100F.
Combustion	Rapid oxidation (burning) accompanied by the release of heat.
Common - ion effect	Suppressing effect an electrolyte has on the ionization of another electrolyte that shares a common ion.
Complex ion	Ion in which a central metal ion is bonded to one or more ions or molecules.
Complexing	The use of chelating or sequestering agents to form relatively loose chemical bonding as a means of treating certain pollutants such as nickel, copper, and cobalt.
Composting	The controlled biological decomposition of organic solid wastes under aerobic (in the presence of oxygen) conditions.Organic materials are transformed into soil enhancers such as humus and mulch.
Compound	Two of more elements combined; a substance having different properties than of the elements used.
Concentrated	Having a large ratio of solute to solvent.
Concentration	In solutions, the mass, volume, or number of moles of solute present in proportion to the amount of solvent or total solution Common measures are: molarity, normality, percent, molality, and by specific gravity scales.
Condensate	Water obtained by evaporation or a product that has changed from a gaseous or vaporous form to a liquid form.
Condensation	The process of vapor molecules forming a liquid.
Condensation reaction	Chemical reaction in which one of the products is water or ammonia, also known as a dehydration reaction.
Condensed formula	Chemical formula in which atom symbols are listed in the order they appear in the molecular structure, with limited bond dashes.
Conductance	A measure of the conducting power of a solution equal to the reciprocal of the resistance. The resistance is expressed in ohms.
Conductivity	Ability of a material to carry current or heat.
Conductor	Material which permits the flow of energy (e.g., electrical conductor, thermal conductor).
Conformer	An isomer that differs from another isomer by rotation around a single bond.
Congener	Member of the same group of elements of the periodic table (e.g., iodine and chlorine).
Conjugate acid	A substance which can lose a H+ ion to form a base.
Conjugate base	A substance which can gain a H+ ion to form an acid.
Conjugate	Multiple chemistry definitions, referring to Bronsted acids and bases, a compound formed by combining other compounds, or the overlap of p - orbitals across a sigma bond.
Conservation of energy	Law which states energy can change forms but may not be created or destroyed.
Conservation of mass	Law that states, in a closed system, matter can change forms but not be created or destroyed.
Constitution	The types and totals of atoms which makeup a molecule.
Contact coagulation	A water clarification process which involves the addition of a coagulant with appropriate mixing for the purpose of floc formation within a filter media, which will be periodically back-flushed to permit the separation of the resulting solids from the main wastewater stream.
Contamination	A general term signifying the introduction into water of microorganisms, chemicals, wastes or sewage which renders the water unfit for its intended use.
Continuous spectrum	A spectrum of all the colors of light.
Contract	To become smaller, closer together
Controlled variable	Variable that a scientist holds constant in an experiment; the control or constant variable
Conversion factor	Numerical ratio that converts a measurement from one unit into another.
Cooling tower	A device for cooling water through a combination of sensing and evaporative heat transfer. Water passes over a number a wooden or plastic racks known as “fill”, that act as a heat-transfer surface.
Coordinate bond	Covalent bond between two atoms in which one atom supplies both electrons for the bond.
Coordination compound	Compound containing one or more coordinate bonds.
Coordination number	Number of atoms bonded to a central atom.
Corrosion inhibitor	An additive or a system used for protecting metal surfaces from chemical attack by water or other materials producing sulfides or oxides which result in metal fatigue or degradation.
Corrosion	Irreversible damage to a material or tissue due to a chemical reaction.
Corrosive	Having the power to cause irreversible chemical damage upon contact.
Coulomb's law	Law which states the force between two charges is proportional to the quantity of both charges and inversely proportional to the square of the distance between them.
Covalent bond	Chemical link between atoms or ions in which the electron pairs are more or less evenly shared between them.
Covalent compound	Molecule that contains covalent chemical bonds.
Covalent radius	Value assigned to an atom such that the sum of the covalent radii of atoms A and B is (approximately) the A-B bond length.
Crenation	Forming a scalloped shape upon exposure to a hypertonic solution.
Critical micelle concentration	The solution concentration of a surfactant at which micelles start to form in that solution. (see RFF 705.10.03 - SURFACE TENSION).
Critical point	Critical state; point at which two phases of matter become indistinguishable from one another.
Critical pressure	The lowest pressure required to transform a gas into a liquid at the critical temperature.
Critical temperature	One of three parameters (critical pressure and critical molar volume being the other two) defining the point at which random thermal molecular motion become so violent that attractive forces are unable to bring about condensation even when the molecules are squeezed together; a temperature above which a vapor cannot be turned into a liquid no matter how much pressure is applied.
Critical mass	The amount of a specific radioactive material it takes to create a chain reaction.
Crystal field splitting	The difference in energy between the d orbitals of ligands.
Crystal	Matter in which atoms, ions, or molecules are packed into an ordered, repeating three - dimensional pattern.
Crystallize	Solidification of matter into the highly ordered form of a crystal.
Current	A movement of electrons through a conductor. Measured in amperes.
Cyrogenics	Study of matter at extremely low temperatures

D

Dalton's Law	Relation stating the total pressure of a gaseous mixture equals the sum of the partial pressure of the component gases.
Dative bond	Covalent bond between atoms in which one atom provides both electrons for the bond.
Daughter isotope	In a nuclear equation the compound remaining after the parent isotope (the original isotope) has undergone decay. A compound undergoing decay, such as alpha decay, will break into an alpha particle and a daughter isotope.
De Broglie Equation	Equation describing the wave properties of matter, stated as wavelength equals Planck's constant divided by the product of mass and velocity.
De Broglie's hypothesis	States that electrons around atoms are in wave formation.
Decant	To remove the liquid portion of a settled mixture without disturbing the sediment.
Decantation	Method of separating mixtures by removing the liquid layer from a precipitate.
Decay	Change of an element into a different element, usually with some other particle(s) and energy emitted.
Dechlorination process	A process by which excess chlorine is removed from water to a desired level. Usually accomplished by chemical reduction, by passage through carbon beds or by aeration at a suitable pH.
Decomposition	When a complex molecule becomes broken apart to create two or more smaller ones.
Decomposition reaction	Chemical reaction in which a single reactant yields two or more products.
Deflagration	Type of combustion in which flame propagation is less than 100 m/s and overpressure is less than 0.5 bar.
Degradable	That which can be reduced, broken down or chemically separated.
Degreasing	The process of removing greases and oils from sewage, waste, and sludge.
Dehydration	A reaction in which the elements that make up water (twice as many hydrogen as oxygen atoms) are removed from an organic compound.
Dehydration reaction	Chemical reaction between two compounds in which one of the products is water.
Deliquescence	Process by which a soluble substance picks up water vapor from the atmosphere to form a solution.
Delocalized electron	Any electron in an ion, atom, or molecule that is no longer associated with a particular atom or single covalent bond.
Demineralization	Removal from water of mineral contaminants. Methods include ion exchange, flash distillation, electrodialysis, or reverse osmosis.
Demulsibilty	A measure of a fluid's ability to separate from water.
Denature	When the structure of proteins break down from exposure to heat.
Dense	A compact substance or a substance with a high density.
Density	Mass per unit volume of a substance.
Dependent variable	Variable being measured (tested) in response to changing the independent variable.
Deposition	Settling of sediment or particles onto a surface or the phase change from the vapor to solid phase.
Deprotonation	Chemical reaction in which a compound loses a proton (H+).
Derived unit	An SI unit made from a combination of the base units (e.g., Newton is kg·m/s2).
Desiccant	Chemical agent that picks up water, often used for drying.
Desublimation	Phase change from vapor to solid.
Detention time	The time allowed for solids to collect in a settling tank. Theoretically detention time is equal to the volume of the tank divided by the flow rate.
Detergent	A substance used for removing dirt. Detergents differ from soaps in that detergents are compounds that are derived from sulfur-containing organic acids.
Deuterium	The isotope of hydrogen that has one neutron.
Dew point	The temperature at which the condensation of a vapor begins; the term is usually applied to condensation of moisture from the water vapor in the atmosphere.
Dextrorotatory	Able to rotate plane-polarized light in a clockwise fashion.
DI water	Deionized water, having had all the ions removed.
Dialysis	The separation of a colloid from a substance in solution by allowing the solution to diffuse through a semipermeable membrane.
Diamagnetic	Not attracted to a magnetic field, generally because the material does not contain unpaired electrons.
Diatomaceous earth	A filter medium used for filtration of effluents from secondary and tertiary treatments, particularly when a very high grade of water for reuse in certain industrial purposes is required; used as an absorbant for oils and oily emulsions in some wastewater treatment designs; also used historically in preparing standard suspensions for turbidity measurements.
Diffusion	The gradual mixing of the molecules of 2 or more substances by random molecular motion.
Digestion	The biochemical decomposition of organic matter which results in the formation of mineral compounds and simple organic compounds.
Diluent	The thinning agent used to dilute a fluid, usually water.
Dilute	To thin out, or having been thinned out; less than full strength.
Dilute sewage	Sewage containing less than 150 ppm of suspended solids and BOD (weak sewage).
Dilution	When a substance, called a solvent, is added to a suspension to reduce the concentration.
Dimer	A molecule or compound formed by the combination of two identical simple molecules.
Diode	A component that readily passes current in one direction but opposes current flow in the opposite direction.
Dipole	Produced from an unequal sharing of electrons in a molecule in which there will be a region of partial positive charge and a separate region of partial negative charge.
Dipole moment	Measure of the separation of two opposite electrical charges.
Dipole	A separation of electrical or magnetic charges.
Dipole-dipole forces	Intermolecular forces that exist between polar molecules. Active only when the molecules are close together. The strengths of intermolecular attractions increase when polarity increases.
Diprotic acid	Acid that can donate two hydrogen atoms or protons per molecule in an aqueous solution.
Direct current (dc)	A non-oscillating current that flows continually in one direction through a circuit
Direct proportion	Relation between two variables such that their ratio is a constant value.
Disaccharide	Carbohydrate formed when two monosaccharides bond, removing a molecule of water from their structure.
Disinfection	Effective killing by chemical or physical processes of all organisms capable of causing infectious disease. Chlorination is the disinfection method commonly employed in sewage-treatment processes.
Dispersion	A stable distribution of fine solid particles in a liquid.
Dispersion forces (also called London dispersion forces)	Dispersion is an intermolecular attraction force that exists between all molecules. These forces are the result of the movement of electrons which cause slight polar moments. Dispersion forces are generally very weak but as the molecular mass increases so does their strength.
Displacement reaction	Chemical reaction in which the cation or anion of one reactant is replaced by one from another reactant.
Disproportionation	Chemical reaction (usually redox) where a molecule forms two or more dissimilar products.
Dissociation	In an aqueous solution, the separation of a compound into ions.
Dissociation reaction	Chemical reaction in which a reactant breaks into two or more parts.
Dissolve	A solute passing into solution, usually a solid going to the liquid phase.
Dissolved oxygen (DO)	The oxygen dissolved in sewage, water, or other liquid, usually expressed in milligrams per liter or percent of saturation. It is the test used in BOD determination. dissolved solids: the total amount of dissolved material, organic and inorganic, contained in water or wastewater. Excessive dissolved solids make water unpalatable for drinking and unsuitable for industrial use. Measurements are expressed as ppm or mg/L.
Distillate	Vapor formed by a distillation, which may be condensed into a liquid for collection.
Distillation	The process of heating a liquid to its boiling point, removing the vapors through a cooling and condensing apparatus, and finally collecting the condensed liquid in a separate receiver. It is commonly used for the separation of two or more liquids in a mixture, or for the separation of the solvent from dissolved substances.
Distilled water	Water that has been purified by distillation (boiling the water off as steam and condensing it back to a liquid, leaving the impurities behind). Having been boiled, it is also sterile.
Divalent cation	Positive charged ion with a valence of 2.
Dopamine	One of many neurotransmitters that is essential in the functioning of the central nervous system and is often considered to be the primary reward neurotransmitter in the brain. It is the precursor to norepinephrine.
Dose	The measured quantity of a substance, such as a drug, taken at one time.
Double bond	Chemical bond in which two electron pairs are shared between two atoms.
Double replacement reaction	Chemical reaction in which two reactants exchange anions/cations to form two new products using the same ions.
Drawdown	The act, process, or result of depleting, as in the drawdown of oil reserves.
Dry ice	The solid form of carbon dioxide
Ductile	The ability of a substance to be drawn out to form a thin wire.
Ductility	Property of a metal in which it can be stretched without breaking.
DuNouy ring tensiometer	A piece of equipment which measures the force required to remove a ring of precisely known dimensions from a liquid surface. This force is directly related to the surface tension of that liquid.
Dye	A substance used to give color to cloth, plastics, paper, or other materials.Dye may be made from plants or by synthetic chemical reactions.
Dynamic equilibrium	Chemical equilibrium between the forward and reverse reaction in which the rates of reaction are equal to each other.

E

EDTA titration (EDTA)	Ethylenediaminetetraacetic acid (or its salts). A standard method of measuring the hardness of a solution
Effective nuclear charge	Net charge an electron experiences in an atom that has multiple electrons.
Effervescence	Foaming or bubbling when gas is evolved by a liquid or solid.
Efflorescence	Process by which a hydrate loses water of hydration.
Effluent	A liquid that has passed through a processing operation.
Effluent limitation	Any restriction (including schedules of compliance) established by a state or EPA on quantities, rates, and concentrations of chemical, physical, biological, and other constituents which are discharged from point sources into navigable water, the waters of the contiguous zone, or the ocean.
Effusion	Movement of gas through a pore or capillary into a vacuum or another gas.
Elasticity	Physical property of matter describing the ability to return to original shape after deformation.
Electrical conductivity	Measure of a substance's ability to carry an electrical current.
Electrical resistivity	Measure of how much a material resists carrying an electrical current.
Electricity	A form of energy coming from charges.
Electrochemical	Describes any effect concerned with the electrical properties of solutions and the ions in solutions.
Electrochemical cell	Device that generates a potential difference between electrodes via chemical reactions.
Electrochemistry	Scientific study of reactions and species formed at the interface between an electrolyte and a conductor, where electron transfer occurs.
Electrode	The anode or cathode of an electrical cell, the device that moves electrons into or out of a solution by conduction.
Electrolysis	Changing the chemical structure of a compound using electrical energy.
Electrolyte	A substance that, when dissolved in water produces a solution that conducts electricity.
Electrolytic cell	Type of electrochemical cell in which the flow of electric energy from an external source enables a redox reaction.
Electromagnetic radiation	Light; self propagating energy that has electric and magnetic field components.
Electromagnetic spectrum	Complete range of wavelengths which light can have. These include infrared, ultraviolet, and all other types of electromagnetic radiation, as well as visible light.
Electromotive force	EMF, the electric potential generated by either an electrochemical cell or changing magnetic field.
Electron	A particle of the atom that has a negative charge. The electron is not a part of the nucleus, but moves around in an orbit around the nucleus.
Electron affinity	Measure of the ability of an atom to accept an electron.
Electron capture (EC)	Form of radioactive decay in which the atomic nucleus absorbs a K or L shell electron, converting a proton into a neutron.
Electron cloud	Region of negative charge surrounding the atomic nucleus that has a high probability of containing electrons.
Electron configuration	Description of the population of the electronic energy sublevels of an atom.
Electron density	Representation of the probability of finding an electron in a specific region around an atom or molecule.
Electron domain	The number of lone electron pairs or bond locations around an atom or molecule.
Electron geometry	Structure of a compound based on the arrangement of its electrons.
Electron pair repulsion	Principle that electron pairs surrounding a central atom orient themselves as far apart as possible; used to predict geometry.
Electron spin	Property of an electron related to its spin about an axis, described by a quantum number as either +1/2 or -1/2.
Electronegativity	Property of an atom that reflects its ability to attract electrons in a chemical bond.
Electrophile	Atom or molecule that accepts an electron pair to form a covalent bond.
Electrophoresis	A method of separating large molecules (such as DNA fragments or proteins) from a mixture of similar molecules. An electric current is passed through a medium containing the mixture, and each kind of molecule travels through the medium at a different rate, depending on its electrical charge and size. Separation is based on these differences.
Electroplating	Process of adding a metal coat to a material by using a reduction reaction.
Electrostatic	Having to do with the positive and negative charges on species such as electrons or ions.The important principle is that like charges repel and opposite charges attract.
Electrostatic forces	Forces between particles due to their electrostatic charges.
Electrum	A natural alloy of gold and silver.
Element	A substance that cannot be resolved into two or more other substances; a substance made up of atoms with the same atomic number.
Element symbol	The one or two letter abbreviation of a chemical element (e.g., H, Cl).
Elementary reaction	Chemical reaction in which reactants form products in a single step without a transition state.
Emission spectrum	Range of wavelengths emitted by an atom stimulated by electricity or heat.
Emission	Product of a combustion reaction, aside from heat and light (e.g., carbon dioxide).
Emollient	A substance that softens or smoothes.
Empirical formula	The simplest whole number ratio of elements in a compound, ie CH2.
Emulsifier	A substance that promotes the dispersion of small globules of one liquid in another liquid when the two liquids will not mix.
Emulsion polymerization	A heterogeneous, free-radical polymerization process in which the bulk of the polymeric product in formed inside micelles.
Emulsion	A liquid system in which one liquid is finely dispersed in another liquid in such a manner that the two will not separate through the action of gravity alone.
Enantiomer	One of a pair of non-superimposable, mirror-image stereoisomers.
End point	That stage in the titration at which an effect, such as a color change, occurs, indicating that a desired point in the titration has been reached.
Endothermic	Process that absorbs heat from its surroundings as the reaction proceeds.
Endothermic reaction	Takes more energy to start it than it gives back. A reaction that needs energy to keep it going.
Enediol	An alkene enol with a hydroxyl group attached to both carbon atoms of the C=C bond.
Energy	The ability to do work and transfer heat.
Energy level	The current level of energy an electron has within an atom.
Enrichment	The addition of nitrogen, phosphorous, and carbonaceous compounds, or other nutrients into a lake or other waterway that greatly increases the growth potential for algae and other aquatic plants. Most frequently, enrichment results from the inflow of sewage effluents or from agricultural runoff.
Enthalpy change	The energy change of a system at constant pressure.
Enthalpy of atomization	Quantity of enthalpy change when chemical bonds are broken in a compound to form individual atoms.
Enthalpy of reaction	Difference between total enthalpy of products and total enthalpy of reactants of a chemical reaction.
Enthalpy	Thermodynamic property of a system that is the sum of the internal energy and the product of pressure and volume.
Entropy	Measure of the disorder of a system.
Enzymatic	Relating to the activity of enzymes, which are biological catalysts that play crucial roles in most biological processes, including metabolism and gene expression.
Enzyme	A biological catalyst that will increase the rate of a chemical reaction, but is not consumed in the course of a reaction.These catalysts are at least hundreds of times more efficient than any man-made catalyst used in industrial processes.
EP additive	A lubricant additive or system which prevents sliding metal surfaces from seizing under conditions of extreme pressure and force.
Epimer	One of two steroisomers with more than one chiral center that differ in stereochemical configuration at only one.
Equilibrium	When the reactants and products are in a constant ratio. The forward reaction and the reverse reactions occur at the same rate when a system is in equilibrium.
Equilibrium constant	Value that expresses how far the reaction proceeds before reaching equilibrium. A small number means that the equilibrium is towards the reactants side while a large number means that the equilibrium is towards the products side.
Equilibrium expressions	The expression giving the ratio between the products and reactants. The equilibrium expression is equal to the concentration of each product raised to its coefficient in a balanced chemical equation and multiplied together, divided by the concentration of the product of reactants to the power of their coefficients.
Equivalence point	Point in a titration where the titrant completely neutralizes the analyte.
Essential amino acid	Amino acid needed in the diet because an organism cannot synthesize it.
Ester	RCO2R′, where R is the hydrocarbon parts of the carboxylic acid and R′ is the alcohol.
Ether	Organic compound containing two aryl or alkyl groups bound to an oxygen, R-O-R'.
Eutectic	Homogeneous solid mixture of at least two types of atoms or molecules that form a superlattice (usually a mix of alloys).
Evaporation	Changing of a liquid to a vapor at any temperature below its boiling point.
Excess reactant	Reactant left over in a reaction because it is present in a great amount than needed to react with the limiting reactant.
Excited state	Atom, ion, molecule, or subatomic particle in a higher energy level than its ground state.
Excretion	The process of ridding the body of metabolic waste products.
Exergonic process	A process that liberates energy.
Exergonic	Releasing energy to its surroundings.
Exothermic	Process that gives off heat to the environment.
Exothermic process	A thermodynamic process in which heat flows from a system to the surroundings.
Exothermic reaction	A chemical reaction that releases heat.
Exothermic	Releasing energy to the environment in the form of heat; a type of exergonic process
Exponentiation	Raising something to a power.
Extensive property	Property of matter that depends on the quantity of matter that is present (e.g., volume).

F

F orbital	Electron orbital with l = 3 for the angular momentum quantum number,
Facultative	Having the power to live under different conditions either with or without oxygen.
family (of elements)	Elements found in the same column of the periodic table, also known as a group of elements.These elements will have similar properties.
Faraday constant	A physical constant equal to the electric charge of one mole of electrons, 96485.33 C/mol.
Fat	A solid ester of a long-chain carboxylic acid with glycerol.
Fatty acid	A carboxylic acid with a long hydrocarbon side chain.
Feedstock	Any unprocessed material used as a supply for a manufacturing process.
Fenfluramine	Amphetamine-like component of fen-phen that suppresses appetite by increasing seratonin levels in the brain.
Filter	To separate an insoluble solid from a liquid by pour it through a solid (usually paper) to trap the solid particles and separate them from the liquid.
Filter backwash	The reversal of flow though a filter to wash clogged material out of the filter medium and reduce conditions causing loss in flow through the filter.
Filtration	The process of separating solids from a liquid by means of a porous substance through which only the liquid can pass.
Fire point	The lowest temperature a vapor will initiate and sustain combustion.
First law of thermodynamics	Law which states the total energy of a system and its surroundings is a constant value; the law of conservation of energy.
Fission	The splitting of an atomic nucleus, which results in two or more lighter nuclei and a release of energy.
Flame test	An analytical technique used to identify ions based on their emission spectrum in a flame.
Flammable	Easily ignited or capable of sustained combustion.
Flash point	The lowest temperature at which vapors from a volatile liquid will ignite on application of an ignition source under specified conditions. Flash point is a specification for some alkylates.
Floatation	The process of removing finely divided particles from a liquid suspension by agitating the liquid with gas bubbles thus increasing the buoyancy of the particles, and concentrating them at the surface of the liquid medium.
Floc	A very fine, fluffy mass formed by the aggregation of fine suspended particles.
Flocculation	The process of separating suspended solids from wastewater by chemical creation of a coagulated, or flocculent masses.
Flowrate	Usually expressed as liters/minute (gallons/minute) or liters/day. Design flowrate is that used to size the wastewater treatment process. Peak flowrate is 1.5 to 2.5 times design and relates to the hydraulic flow limit and is specified for each plant.
Fluid	A substance which yields readily to any force which tends to alter its shape; fluids possess no definite shape; the term includes both liquids and gases.
Fluorescence	Luminescence released when an atom absorbs electromagnetic radiation and emits a photon when the electron falls to a lower energy state.
Flux	A material used to promote joining of metals in soldering.
Foam booster	A substance which enhances the quality and/or longevity of a foam.
Foam	A substance containing gas bubbles trapped within a liquid or solid.
Force	An entity that when applied to a mass causes it to accelerate. Sir Isaac Newton's Second Law of Motion states: the magnitude of a force=mass*acceleration.
Formal charge	The difference between the number of valence electrons of an atom and the number of electrons associated with the atom (e.g., in a chemical bond).
Formation reaction	Reaction in which one mole of a product is formed.
Formazin	A polymer suspension used as the standard for turbidity.
Formazin nephelometric unit (FNU)	An industry standard unit measurement used in the European Union, equivalent to NTU.
Formazin turbidity unit (FTU)	A measure of water turbidity equivalent, but not equal, to Jackson Turbidity Units (JTU).
Formula	A shorthand way of showing the composition of a substance with the use of symbols and numerical subscripts.
Formula mass / weight	The sum of the atomic weights of the atoms in a compound's empirical formula.
Formulation	A blend of a number of base chemicals and additives designed to accomplish a specific purpose.
Fractional distillation	Process which separates components of a mixture according to their boiling points.
Free electron	Electron which is not attached to a nucleus.
Free energy	The amount of internal energy of a system that is available to do work.
Free radical	An atom or molecule with an unpaired electron.
Freezing point depression	Lowering the freezing point of a liquid by adding another compound to it.
Freezing point	Temperature at which a liquid transitions to a solid (not always the same as melting point).
Freezing	Process in which a liquid changes to a solid.
Frequency	The number of complete waves passing a point in space in a given amount of time.
Fuel	A material that can be burned to provide a source of energy.
Fumigant	A gaseous substance used to disinfect an object or to destroy pests.
Functional groups / moiety	Group of atoms in a molecule that are responsible for characteristic reactions and properties.
Fungicides	A chemical that kills fungi or prevents them from growing.
Fuse	A protective device containing a short piece of wire that melts and breaks when current through it exceeds a rated value, thus de-energizing the circuit.
Fusion	Combining light atomic nuclei to form a heavier nucleus, accompanied by the release of energy.

G

Galvanic cell	Electrochemical cell where reactions between dissimilar conductors occur through a salt bridge and electrolyte.
Galvanize	The process of covering iron with a coat of zinc to make it less reactive to air and water.
Galvanometer	A device that is very sensitive and able to detect even small flows of electrons through a wire.
Gamma radiation	High energy ionizing photons, originating from the atomic nucleus.
Gamma ray	Electromagnetic radiations beyond the X-rays in frequency. They are usually produced in nuclear reactions.
Gardner	A unit of color density. Measured by comparison of the material to be analyzed against standards of known intensity.
gas chromatography	An analytical chemistry technique in which a sample is vaporized and passed through a column whose walls are covered with a sticky organic solvent; different chemicals in the sample have different affinities for the solvent and separate as they pass through the column.
Gas constant (R)	The constant in the Ideal Gas Law; R = 8.3145 J/mol·K.
Gas	A fluid having neither independent shape nor volume, but tending to expand indefinitely. The word is often used to denote anesthetics, combustibles (gasoline), poisonous materials, etc., whether liquid or solids at ordinary temperatures.
Gasohol	A mixture of 90% gasoline and 10% ethyl alcohol that is used as an automotive fuel.
Gasoline	A volatile, flammable, liquid mixture of hydrocarbons, obtained from petroleum, and used as fuel for internal-combustion engines.
Gay-Lussac's law	Form of the ideal gas law that states the pressure of an ideal gas is directly proportional to its absolute (Kelvin) temperature when volume is held constant.
Geiger counter	Instrument that measures radiation output.
Gel	A colloid in which the dispersed phase has combined with the continuous phase to produce a semisolid material as a jelly; a colloid formed by coagulation of a sol.
Gene	The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or RNA molecule).
Geometric isomer	Molecules with the same number and type of atoms as each other, but with different geometrical configurations. Also called cis-trans or configurational isomerism.
Gibb's free energy	The energy of a system that is available to do work at constant temperature and pressure.
Glass	An amorphous solid.
Glucose	A 6-carbon sugar that plays a major role in cell metabolism.
Glycogen	A polysaccharide the body uses for energy storage; it is made up of chains of glucose molecules. When the body has depleted the free glucose in the blood, the liver breaks down glycogen into more glucose.
Glycolipid	A lipid covalently linked to a sugar or polysaccharide. These biomolecules are important parts of animal cell membranes.
Glycolysis	A complex biochemical process in which one molecule of glucose is anaerobically converted into two molecules of pyruvate and energy in the form of ATP.
Glycosidic bond	A covalent bond between a carbohydrate and a functional group or another molecule.
Grab sample	A single sample of wastewater taken at neither set time nor flow.
Graham's Law	Relation stating the rate of effusion of a gas is inversely proportional to the square root of its molecular mass or density.
Grain alcohol	Purified form of ethyl alcohol made from distilling fermented grain.
Gram molecular mass	The mass in grams of one mole of a molecular substance.
Graphite	The most stable allotrope, or form of carbon, having a hexagonal type linking of atoms with relatively strong bonds to 3 neighboring carbon atoms, and a much weaker bond to a fourth carbon atom.
Gravimetric analysis	A set of quantitative analytical techniques based on measurement of a sample's mass.
Green chemistry	Branch of chemistry concerned with lessening the environmental effect of chemicals, including development of new materials and processes.
Ground state	The lowest energy state of an atom, ion, molecule, or subatomic particle.
Ground wire	A conductor leading from electrical equipment to a low resistance connection with the earth.
Group	A family of elements with similar chemical properties, represented by a vertical column in the periodic table.

H

Haber process	Method of making ammonia or fixing nitrogen by reacting nitrogen and hydrogen gas
Half-cell	An oxidation or reduction reaction that occurs at an electrode.Two half-cells must be combined to form an electrochemical cell.
Half-life (t1/2)	The time required for concentration of one substance to reach half of its initial value.The time it takes for one half of a substance to be metabolized and/or excreted from the body.
Half-reaction	A reaction that shows the electrons involved in an oxidation or reduction step of a reaction.
Halide	A negatively charged ion of the group VIIA elements.
Halide ion	A singlet halogen atom, which has a charge of -1 (e.g., Cl)
Halogen	The group VIIA elements in the periodic table.
Halogen	An element in Group VII A of the periodic table (e.g., Br, Cl).
Halogenated hydrocarbon	A hydrocarbon that contains one or more halogen atoms.
Hard water	Water that contains high amounts of calcium and/or magnesium cations.
Hardness	1) A characteristic of water, imparted by salts of calcium, magnesium, and iron, such as bicarbonates, carbonates, sulfates, chlorides, and nitrates that cause curdling of soap, deposition of scale in boilers, damage in some industrial process, and sometimes objectionable taste. It may be determined by a standard laboratory procedure or computed from the amounts of calcium and magnesium as well as iron, aluminum, manganese, barium, strontium, and zinc; expressed as equivalent parts per million of calcium carbonate. 2) Property of matter that determines how easily the substance can be scratched.
Heat	The transfer of (thermal) energy between two objects that are at different temperatures.
Heat capacity	Quantity of heat needed to raise the temperature of a sample by a specified amount.
Heat of formation ( ΔHf)	Amount of heat absorbed or released during formation of a pure substance from its elements at constant pressure.
Heat of fusion ( ΔHfus)	The change in enthalpy (heat) for the conversion of one gram or mole of a solid to a liquid at constant temperature and pressure.
Heavy metal	A general term given to the ions of metallic elements such as copper, zinc, chromium, and aluminum. They are removed from wastewater by forming an insoluble precipitate (usually a metallic hydroxide).
Heisenberg uncertainty principle	Principle that states it is impossible to determine both the position and momentum of a particle at once with perfect accuracy.
Henderson - Hasselbalch equation	An approximation that relates the pH or pOH of a solution, the pKa or pKb, and the ratio of concentration of dissociated species.
Henry's Law	Law that states the mass of a gas that will dissolve into solution is directly proportional to the partial pressure of the gas above the solution.
Hertz (Hz)	In electrical/electronic applications with alternating current, a unit of frequency where 1 Hz equals one cycle per second.
Hess's Law	Law that states the energy change in an overall reaction equals the sum of the energy changes in its individual (partial) reactions.
heterocycle	A compound containing at least one ring that consists of both carbon and non-carbon atoms .
Heterogeneous	Describes a material or substance or chemical reaction which is not the same throughout in its properties, composition, or state of matter.
Heterogeneous mixture	A mixture that lacks a uniform composition such that at least two components are present with identifiable properties.
Heterogeneous reaction	Chemical reaction in which reactants are different phases from each other.
Homeopathy	A system of disease treatment involving application of minute doses of a remedy that, in a healthy person, would produce symptoms of the disease.
Homogeneous	Describes a material or substance or chemical reaction which is the same throughout in its properties, composition, or state of matter.
Homopolymer	Polymer in which every mer unit is identical.
Hybrid orbital	Orbital formed by the combination of two or more atomic orbitals.
Hybridization	A mixing process, often applied to description of atomic orbitals, producing orbitals that have characteristics intermediate between the various types of orbitals involved.
Hydrate	A crystalline solid with molecules of water trapped in the solid state structure, which can often be removed partly or completely by relatively gentle heating.
Hydration	Having solvent molecules of water surrounding and becoming attached to ions or molecules of the solute.
Hydration reaction	Reaction in which a hydrogen and hydroxyl ion are attached to a carbon in a C-C double bond.
Hydrocarbon	A chemical compound containing only hydrogen and carbon; the largest source of hydrocarbons comes from petroleum crude oil.
Hydrogen bond	A special situation that exists between the hydrogen atom in one molecule (like water) and the oxygen atom in another molecule (like another water molecule). This bond is ten times weaker than the covalent bond, and ten times stronger than the van der waals force. The hydrogen bond caused water to have its unusual properties of high boiling point, high melting point, high surface tension, and its formation of the six- sided ring structure in ice. The latter causes water to expand upon freezing, become less dense, and float in water.
Hydrogen ion concentration	The normality of a solution with respect to hydrogen ions, H+; it is related to acidity measurements in most cases by the equation pH= log 1/2[1/(H+)] where H+ is the hydrogen ion concentration in gram equivalents per liter of solution.
Hydrogenation	The infusing of unsaturated or impure hydrocarbons with hydrogen gas at controlled temperatures and pressures for the purpose of obtaining saturated hydrocarbons and/or removing various impurities such as sulfur and nitrogen.
Hydrolysis	Cleavage of a covalent bond brought about by water; the H- and -OH of water typically become attached to the respective cleavage fragments.For example:
Hydrolyze	To add hydrogen or hydroxyl to a substance.
Hydrometer	Instrument used to measure the relative densities of two liquids.
Hydronium ion	The H3O+cation.
Hydrophile	A material having an affinity for, attracting, adsorbing or absorbing water. The opposite of hydrophobe.
Hydrophile-Lipophile balance	A measure of the relative simultaneous attraction of an surfactant to both phases of an emulsion.
Hydrophobe	A material lacking affinity for, repelling, failing to adsorb or absorb water. The opposite of hydrophile.
Hydrophobic	Property of repelling water.
Hydrotrope	A substance, such as sodium xylene sulfonate, which increases the aqueous solubility of surfactants and other substances. Hydrotropes are sometimes used to reduce a systems viscosity. (see RFF 705.10.08 - HYDROTROPES).
Hydroxyl group	Functional group consisting of a hydrogen atom covalently bonded to an oxygen atom (-OH).
Hydroxyl number	A measure of the hydroxyl content of ethoxylates. Measured titrimetrically. Usually used for molecular weight determinations.
Hydroxyl radical	An oxygen and hydrogen atom occurring as a group (OH-).
Hygroscopic	Able to absorb or adsorb water from the surroundings.
Hypertonic	Having higher osmotic pressure than another solution.
Hypothesis	A scientific "hunch," a tentative explanation of or prediction derived from experimentation.

I

Ideal gas constant	Physical constant in the Ideal Gas Law, equal to the Boltzmann constant but with different units.
Ideal gas law	PV=nRT，Describes the relationship between pressure (P), temperature (T), volume (V), and moles of gas (n). This equation expresses behavior approached by real gases at low pressure and high temperature.
Ideal gas	Gas in which molecules have negligible size and kinetic energy dependent only on temperature.
Immiscible	Property of two substances being unable to combine to form a homogeneous mixture; unable to mix
Impedance	Total opposition to flow of current, measured in ohms; combined effort of resistance, inductance, and capacitance.
Incineration	Burning of wastes under controlled high temperatures and oxygen levels that results in their complete combustion; not the same as burning leaves in the back yard or wood in the fireplace.
Independent variable	The variable that is controlled or changed in an experiment to test its effect on the dependent variable.
Indicator	A compound that changes color at a particular pH, or over a particular narrow range of pH, used to show titration end points.
Inductive effect	Effect a chemical bond has on the orientation of adjacent bonds in a molecule.
Industrial sewage	Sewage in which industrial wastes predominate.
Influent	Sewage, water or other liquid, either raw or partly treated, flowing into a reservoir basin, or treatment plant or any part thereof.
Inhibitor	Substance that slows or prevents a chemical reaction.
Inorganic chemistry	Study of chemistry of molecules of non-biological origin (not containing C-H bonds).
Insoluble	Unable to dissolve in a solvent.
Intensive property	Property of matter that is independent of the quantity of matter in a sample.
Intercalation	The binding of a molecule between adjacent base pairs in DNA.
Intermediate	Molecules that exist only during a chemical reaction; not before or after the reaction.
Intermolecular	Between molecules.Intermolecular forces are those forces between molecules.
Intermolecular force	The sum of all forces between neighboring molecules.
Internal energy	The total energy (U) of a closed system.
Intramolecular	Refers to a characteristic within one molecule or ion, referring only to the atoms in the molecular or ion.
Intramolecular force	Force within molecules. Forces caused by the attraction and repulsion of charged particles.
Intrinsic property	Property of matter that is independent of the quantity of matter present.
Inverse proportion / relationship	Relationship between variable such that their product is a constant value.
Ion	An isolated electron or positron; an atom or molecule which by loss or gain of one or more electrons has acquired a net electric charge.
Ion exchange	A chemical reaction in which mobile hydrated ions of a solid are exchanged, equivalent for equivalent, for ions of like charge in solution. The process can be used to remove ionic pollutants from wastewater.
Ion-dipole force	Intermolecular force that exists between charged particles and partially charged molecules.
Ion-exchanger	A resin capable of removing unwanted ions and replacing them with more desirable ones.For example, Ca2+or Mg2+, which interfere with the action of soap or detergent can be replaced by Na+, which does not.
Ionic bond	Chemical link between atoms caused by electrostatic force between opposite charged ions.
Ionic compound	Compound formed by ions bonding together due to electrostatic forces (differing electronegativity values).
Ionic equation	Chemical equation in which electrolytes in aqueous solution are written as dissociated ions.
Ionic radius	Half the distance between two ions just touching each other.
Ionic	Pertaining to carrying a net electrical charge at the atomic or molecular level.
Ionization	A process by which a neutral atom or molecule loses or gains electrons, thereby acquiring a net charge and becoming an ion; occurs as the result of the dissociation of the atoms of a molecule in solution or of a gas in an electric field.
Ionization energy	The energy needed to remove an electron from a gaseous atom.
Ionize	When a substance breaks into its ionic components.
Irreversible reaction	A chemical reaction after which the resulting agents cannot be changed back into the reactions ingredients.
Isoelectronic	Chemical species that have the same electronic structure and thus same number of valence electrons.
Isolated system	Thermodynamic system that can't exchange energy or matter outside of the system.
Isomer	Chemical compound that has the same number, and kinds of atoms as another compound, but a different structural arrangement of the atoms.
Isomerization process	Protocol in which straight chain hydrocarbons are converted into branched chain hydrocarbons.
Isotope	Atoms that have the same number of protons, but different numbers of neutrons and thus different atomic weight values.
IUPAC	International Union of Pure and Applied Chemistry, an authority on chemical standards.

J

Jackson turbidity unit (JTU)	A measure of the turbidity of water, proportional to the ppm silica, where 100 ppm silica equals 21.5 JTU. This method was the standard for turbidity for many years; it applied the use of a candle, measuring tube, and the human eye for determining the value. This method has since been replaced by the use of a known turbidity standard, Formazin, and the use of analytical instruments that will detect forward-scattered light and light scattered at 90 degrees.
joule	SI unit of energy equal to the kinetic energy of a 1 kg mass moving at 1 m/s.
JTU	See jackson turbidity unit.

K

Kelvin	The SI Unit of temperature. It is the temperature in degrees Celsius plus 273.15.
Keratin	A fibrous protein produced by chordates. It may be found in hair, skin, claws, and wool.
Ketone	Compound containing a carbonyl functional group (C=O) between two groups of atoms
Ketose	A simple sugar that has the reactions of a ketone.
Kilo	Prefix meaning "one thousand".
Kilogram	Base unit for mass in metric system.
kilopascal (kPa)	Unit of pressure exerted by a 10 g mass on a square centimeter. There are 1000 Pa in 1 kPa.
Kinetic energy	The energy an object has because of its mass and velocity. Objects that not moving have no kinetic energy. (Kinetic Energy=0.5* mass*velocity2.)
Kinetic-molecular theory	A theory of the behavior of matter.
Klett	A unit of color density. Measured by the light absorption of a clear solution using a Klett-Summerson photoelectric colorimeter.
Krafft point	The temperature at which the solubility of an ionic surfactant becomes equal to the critical micelle concentration.

L

Labile complex	A complex ion that quickly reaches equilibrium with ligands in the surrounding solution.
Lagoon	In wastewater treatment, a shallow pond where sunlight, bacterial action, and oxygen interact to restore wastewater to a reasonable state of purity.
Lanthanides	Subset of transition metals characterized by filling of the 4f sublevel, usually atomic number 58 - 71
Laser	Acronym for light amplification by stimulated emission of radiation.A laser is an intense source of light with a very narrow range of wavelengths. The intense light is given off when many ions are stimulated and simultaneously emit a photon at the same wavelength.
Lattice	A regular arrangement of points in space in 3 dimensions.
Lattice energy	Enthalpy change of the process by which opposite - charged ions in a gas combine to form a solid ionic lattice.
Law of chemical equilibrium	An expression of the relationship between the concentration of reactants and products of a chemical reaction mixture at equilibrium.
Law of combining volume	Relation that states the volumes of gases in a chemical reaction are present in the ratio of small integers under conditions where all gases are at the same temperature and pressure.
Law of conservation of energy	Law that states energy can neither be created nor destroyed, although it may change from one form into another.
Law of conservation of mass / matter	Law that states matter in a closed system may be neither created nor destroyed, although it may change forms.
Law of constant composition	Chemistry law that states samples of a pure compound contain the same elements in the same proportions by mass.
Law of definite proportion	Law that states all samples of a compound contain the same proportion of elements by mass.
Law of multiple proportion	Law that states element combine in ratios of small whole numbers to form molecules.
Law	A general rule that explains a body of scientific observations. Laws are stated in words, but expressed by mathematical equations.
Le Chatlier's principle	States that a system at equilibrium will oppose any change in the equilibrium conditions.
Leachate	The solution produced by passing a liquid through a solid, often containing chemicals that have dissolved from the solid to the liquid. As rainwater passes through landfills and associated sediments, various chemical substances may dissolve in the water and penetrate the aquifer and contaminate ground water.
Levorotatory	Able to rotate plane-polarized light in a counterclockwise fashion.
Lewis acid base reaction	Chemical reaction that forms at least one covalent bond between an electron pair donor (Lewis base) and electron pair acceptor (Lewis acid).
Lewis acid	Chemical species that can act as an electron pair acceptor.
Lewis base	A substance that is an electron pair donor.
Lewis structure	Representation of a molecule that uses dots to show electrons around atoms and lines to show covalent bonds.
Ligand	A chemical species that donates or shares at least one electron via a covalent bond with a central ion or atom.
Light	Has both wave and particle properties.
Lime	Any of a family of chemicals consisting essentially of calcium hydroxide made from limestone (calcite) which is composed mostly of calcium carbonate or a mixture of calcium carbonate and magnesium carbonate.
Limewater	Common name for a solution of calcium hydroxide.
Limiting reagent	A chemical in a reaction that is used up before other ingredients in the reaction, thus limiting how much of the resulting substance can be produced.
Limnology	The study of the physical, chemical, meteorological and biological aspects of fresh water.
Line spectra	Spectra generated by excited substances. Consists of radiation with only specific wavelengths.
Lipid	A fatty, waxy or oily non-polar organic compound that is characteristically insoluble in water but readily soluble in organic solvents.
Liquefaction	Process of converting a material from a solid or gas phase into the liquid phase.
Liquid	A state of matter that has a definite size or volume but not a definite shape.
Liter	Unit of volume in the metric system, slightly larger than 1 quart, since 1 liter is 33.2 ounces, or 1 quart is 0.946 liters, to three significant figures.
Litmus	Plant pigment commonly used as an acid base indicator.Litmus is red (or pink) in an acid, and blue in a base.
Litmus paper	Filter paper used as a pH paper that has been treated with a water - soluble dye obtained from lichens.
London dispersion force	Weak intermolecular force between atoms or molecules in close proximity to each other, due to electron repulsion.
Lone pair/unshared pair	Two electrons that are not shared between atoms within a molecule.
Lye	Common name for solution of sodium hydroxide.
Lyophile	A material having an affinity for, attracting, adsorbing or absorbing oil. The opposite of lyophobe.

M

Macromolecule	Name given to a very large, and in most cases biologically important molecule.Molar mass certain to be in the thousands of grams, at least.
Madelung's rule	Rule that describes filling of electron orbitals in atoms due to shielding of nuclear charge by inner electrons.
Main group element	Any of the elements in the s and p blocks of the periodic table.
Malleability	The property of a metal that allows it to be hammered, rolled, pressed or forged.
Malleable	Able to be shaped or pounded with a hammer, usually applied to metals.
Manometer	An instrument for measuring pressure liquids and gasses. It usually consists of a U-shaped tube containing a liquid, the surface of which is in one end of the tube; moves proportionally with changes in pressure on the liquid in the other end. Also, a tube type differential pressure gauge.
Mass	The quantity of matter in a body as measured by its resistance to a change in acceleration; different but proportional to weight.
Mass defect	Difference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons.
Mass number	The relative mass of the isotopes compared to that of Carbon-12 whose mass is 12.0000 g/mol. It is not shown on the periodic chart. It is also equal to the sum of protons + neutrons inasmuch as protons and neutrons each have an atomic mass of 1 g/mol (amu - atomic mass unit).
Mass percentage	Concentration calculated as mass of a component divided by total mass of mixture or solution; w/w%.
Mass spectroscopy	Analytical technique used to separate and/or identify components of a mixture based on mass and electrical charge.
Matter	Anything that has mass and occupies volume.
Measurement	Quantitative or numerical data describing an object or event.
Medicinal chemistry	Branch of chemistry concerned with design, synthesis, and study of pharmaceuticals.
Melting and boiling temperatures	Caused by the van der waals interaction. Solids melt and liquids evaporate when the van der waals forces between molecules are broken.
Melting point	Temperature at which the solid and liquid phase of matter coexist in equilibrium.
Melting	Phase change of matter from solid to liquid.
Meniscus	The curved upper surface of a non-turbulent liquid in a container; it is concave (curves upward) if it wets the container walls, and convex (curves downward) if it does not. For accurate measurements, readings should be taken at the flat center of the meniscus.
Mercaptan	Organic sulfur compound containing an alkyl or aryl group and a thiol group.
Mercapto group	Functional group consisting of a sulfur bonded to a hydrogen; -SH.
Metabolism	Set of biochemical reactions that store chemical energy and convert it into a form an organism can use.
Metabolite	A chemical product of metabolism.
Metal	Substance that has high conductivity and other metallic properties, including tendency to form cations, often identified by group on the periodic table.
Metallic character	Set of chemical properties associated with metals, including the ability to lose outer valence electrons to form cations.
Metallic compound	Chemical compound that contains one or more metal atoms.
Metalloid	Element with properties intermediate between those of metals and nonmetals (e.g., silicon).
Meteorite	A mass of stone or metal that has reached the earth from outer space.
Meter	Either (a) the base unit of length in the SI system or (b) a device used to measure a quantity.
Methanogenic	"Methane (CH4) producing"; methanogenic bacteria use hydrogen and carbon dioxide as energy sources and produce methane and water as a result.
Methyl	Functional group containing a carbon bonded to three hydrogen atoms, -CH3.
Methylated	Having a methyl group (CH3).
Micelle	Colloidal aggregates of surfactant molecules. Micelles first form in a surfactant solution at a well-defined concentration known as the Critical Micelle Concentration.
Micro	A prefix meaning one-millionth of a unit.
Microliter	Unit of volume that is one - millionth of a liter one cubic millimeter.
Micromolar	Approximately 1x10-6 moles/liter.
Micron	Unit of length equal to one-millionth of a meter; a micrometer.
Microorganism	Organisms (microbes) observable only through a microscope; larger, visible types are called macroorganisms.
Microscopic	Seeing the situation at the particle level: atoms, molecules, or ions.
Milligrams per liter (mg/l)	A weight per volume designation used in water and wastewater analysis. 1mg/L = 1ppm.
Millikan oil drop experiment	Measured the actual charge on an electron.
Mineral acid	Any inorganic acid (e.g., sulfuric acid).
Miscible	Soluble or able to be mixed to form a solution, typically applied to fluids.
Mitochondrion	A membrane-bound organelle that carries out oxidative phosphorylation and produces most of the ATP in eucaryotic cells.
Mixture	Composed of two or more substances, but each keeps its original properties.
Moderator	Material that slows or moderates the speed of neutrons.
Mohs scale	A relative scale rating the hardness of a mineral. A mineral with a high Mohs number is able to mark a mineral with a lower Mohs number.
Moiety	Group of atoms in a molecule that are responsible for its characteristic chemical behavior.
Molal	A solution concentration having a mole of solute per 1,000 grams of solvent, usually water.
Molality	A measure of solution concentration expressed in moles of solute per 1,000 grams of solvent.
Molar	An term expressing molarity, the number of moles of solute per liters of solution.
Molar enthalpy of fusion	Energy needed to change one mole of a substance from solid to liquid phase at constant pressure and temperature.
Molar enthalpy of vaporization	Energy needed to change one mole of liquid to the gas phase at constant pressure and temperature.
Molar heat capacity	Heat energy required to raise the temperature of 1 mole of a substance 1 Kelvin.
Molar mass	Mass of one mole of a substance.
Molar volume	Volume of one mole of a substance.
Molarity	The number of moles of solute (the material dissolved) per liter of solution. Used to express the concentration of a solution.
Mole	The amount of substance that contains the same number of elementary particles as are found in exactly 12 g of carbon-12.
Mole fraction	The number of moles of a particular substance expressed as a fraction of the total number of moles.
Mole ratio	Ratio or fraction comparing the numbers of moles of any two components involved in a chemical reaction.
Molecular equation	Balanced chemical equation in which ionic compounds are expressed as molecules rather than ions.
Molecular formula	Shows the number of atoms of each element present in a molecule.
Molecular geometry	Shape of a molecule, based on the relative positions of the atoms.
Molecular mass	The combined mass (as given on the periodic table) of all the elements in a compound.
Molecular orbital	Wave function of an electron in a molecule.
Molecular weight	The sum of the atomic weights of all the atoms in a molecule.
Molecule	The simplest structural unit of a substance that retains the properties of the substance, and is composed of one or more atoms.
Monatomic ion	An ion formed by a single atom.
Monomer	A simple molecule, such as styrene, which has the ability to combine with a number of like or unlike molecules to form a polymer - polystyrene or styrene/butadiene rubber.
Monooxygenase	An enzyme catalyzing the incorporation of one atom from molecular oxygen into a compound and the reduction of the other atom of oxygen to water.
Monoprotic acid	Acid that donates a single proton or hydrogen atom per molecule in aqueous solution.
Monosaccharide	A simple sugar most commonly having 5 or 6 carbon atoms present which cannot be hydrolyzed to simpler sugars.
Most probable number (MPN)	The number of organisms per unit volume that, in accordance with statistical theory, would be more likely than any other number to be yielded with the greatest frequency in a specific test. Expressed as density of organisms per 100 ml. Results are computed from the number of positive findings of coliform-group organisms resulting from multiple-portion decimal-dilution plantings.
Mother liquor	Solution remaining after crystals are removed from a crystallization solution.
MSDS	Acronym for Material Safety Data Sheet, a written document outlining safety information about a chemical.
Multiple bond	A bond formed when two or more pairs of electrons are shared between two atoms.
Muriatic acid	common name for hydrochloric acid, HCl.

N

Nano-	Prefix meaning one billionth or 10-9.
Naphthenes	Cyclic aliphatic hydrocarbons from petroleum with the general formula CnH2n.
Natural abundance	Average percentage of a given isotope naturally occurring on Earth.
Nephelometer	An instrument that measures scattered light in a liquid.
Nephelometric turbidity unit (NTU)	A standard unit of turbidity measurement, equivalent to FNU.
Net ionic equation	Chemical equation that lists only the species participating in the reaction.
Network solid	Material consisting of an array of repeating covalently bonded atoms.
Neurotransmitter	A substance that transmits nerve impulses across a synapse.
Neutral	An object that does not have a positive or negative charge.
neutral solution	Aqueous solution with a pH of 7.
Neutralization	Chemical addition of either acid or base to a solution such that the pH is adjusted to 7.
Neutralization reaction	A reaction between an acid and a base that results in salt and water.
Neutron	A particle found in the nucleus of an atom. It is almost identical in mass to a proton, but carries no electric charge.
Newton (N)	SI unit of force equal to the amount of force needed to accelerate a 1 kg mass 1 m/sec2.
Nitrification	The conversion of nitrogenous matter or free nitrogen into nitrates and ammonia by bacteria.
Nitrogenase	An enzyme system that catalyzes the reaction of molecular nitrogen (N2) to ammonia (NH3).
Nitrosamines	A group of organic compounds with the basic structure NNO, some of which are powerful cancer-causing chemicals.
NM	An abbreviation for nanometers. A nanometer is equal to 10-9 meters.
Noble gas core	Shorthand notation used writing atomic electron configuration in which previous noble gas configuration is replaced by the element symbol in brackets.
Noble gas	Element from Group 8 of the periodic table (e.g., xenon, argon).
Noble gases	A family of elements that makes up column 18 of the periodic table. They are very stable due to their full outer electron shells.
Node	Part of the orbital area in an atom where it is impossible to find an electron.
Nomenclature	The systematic naming of chemical compounds.
Nonbonding electron	Electron in an atom that does not participate in a chemical bond with other atoms.
Non-electrolyte	A substance that dissolves in water to form a solution that is non-conducting.
Non-ionic surfactants	A general family of surfactants so called because in solution the entire molecule remains associated. Non-ionic molecules orient themselves at surfaces not by an electrical charge, but through separate grease-solublizing and water-soluble groups within the molecule.
Nonmetal	Element that does not display metallic properties, typically referring to elements located in the upper right corner of the periodic table.
Nonoxidizing acid	An acid that cannot act as an oxidizing agent.
Nonpolar	Having no poles.Used to refer to a bond or molecule that overall has no separation of electrical charge.
Nonpolar bond	Chemical bond with even distribution of charge such that it does not have positive or negative poles.
Nonpolar molecule	Molecule that has even distribution of charge such that it does not have positive and negative sides.
Nonpolar covalent bond	A bond where elections are equally shared between two atoms.
Nonsettleable matter	The suspended matter which neither settles nor floats to the surface of water in a period of one hour.
Nonsettleable solids	Wastewater matter that will stay in suspension for an extended period of time. Such period may be arbitrarily taken for testing purposes as one hour.
Nonspontaneous reaction	Chemical reaction that cannot occur without input of external work.
Nonvolatile	Substance that does not readily evaporate into a gas under ordinary conditions.
Norepinephrine	A neurotransmitter that increases heart rate, blood pressure, and is related to increased motor activity. It is the precursor to epinephrine.
Normal	A solution concentration of one gram equivalent per liter of solution.
Normal boiling point	Temperature at which a liquid boils at 1 atm of pressure (sea level).
Normal concentration	Either refers to normal concentration in which the concentration of solutes is the same in two samples or refers to gram equivalent weight of a solute in solution (N).
Normal melting point	Temperature at which a solid melts at 1 atm of pressure.
Normality	A measure of solution concentration expressed in equivalent weights of solute per liter of solution.
NTU	See nephelometric turbidity unit.
Nuclear fission	Splitting of atomic nuclei into two or more lighter nuclei, accompanied by an energy release.
Nuclear radiation	Particles and photons emitted during reactions in the atomic nucleus.
Nuclear fusion	when parts of the nucleus of atoms are forced together to create a new one.
Nuclear reaction	When a reaction affects the nucleus of an atom.
Nucleation	Process of vapor droplets condensing into a liquid, bubbles forming in a boiling liquid, or particle accretion to grow crystals.
Nucleon	The particles in the nucleus of an atom.
Nucleophile	Atom or molecule that donates an electron pair to form a covalent bond.
Nucleoside	A biologically important molecule consisting of an amine-containing purine or pyrimidine base joined to ribose, a 5-carbon sugar.
Nucleus	The central part of an atom that contains the protons and neutrons. Plural nuclei.
Nuclide	An atom or ion characterized by the proton and neutron composition of its nucleus.
Null hypothesis	Proposition that there is no effect of a treatment or no relationship between an independent and dependent variable.
Nutraceutical	A food or part of food that confers health or medical benefits.
Nutrient	Materials which are considered essential to the support of biological life.

O

Octane number	Value that indicates resistance of motor fuel to engine knock relative to the knock from isooctane (100) and heptane (0).
Octet	In Lewis structures, the goal is to make almost all atoms have an octet. This means that they will have access to 8 electrons regularly, even if they do have to share some of them.
Octet rule	Principal that atoms in an atomic bond share their 8 outer electrons.
OHM	A unit of electrical resistance equal to that of a conductor in which a current of one ampere is produced by a potential of one volt across its terminals.
Olefin	A hydrocarbon containing a carbon-carbon double bond. Olefins are also known as alkenes.
Oligomer	A molecule that consists of repeating molecular subunits--essentially a polymer but not as long. By analogy, if a yellow brick is a single subunit, the yellow brick road is a polymer, and the yellow brick driveway is an oligomer.
Only electrons flow	To produce ions. The protons are deep down in the nucleus and stay there. (Except in nuclear reactions, but that's another story ). So electrons are either added or subtracted to make ions.
Opacifier	A substance, such as fatty acid esters, which, when added to a clear formulation, renders that formulation opaque - similar to pearlizer.
Open system	A system able to freely exchange matter and energy with its surroundings.
Orbital	A region of space where there is a high probability of finding an electron in an atom or ion.
Organic chemistry	Study of the chemistry of compounds containing carbon chemical bonded to hydrogen.
Organic matter	Chemical compounds based on carbon chains or rings, and also containing hydrogen with or without oxygen, nitrogen, or other compounds.
Organic nitrogen	Nitrogen combined in organic molecules such as protein, amines, and amino acids.
Orthophosphate	An acid or salt containing phosphorus as PO4, such as K3PO4 (potassium phosphate).
Osmosis	Movement of solvent molecules across a semipermeable membrane from a dilute solution to a more concentrated solution, thus diluting it and equalizing concentration on both sides of the membrane.
Oxidant	A reactant that oxidizes or removes electrons from another reactant in a redox reaction.
Oxidation	In a broad sense oxidation is the increase in positive valence of any element in a substance. On the basis of the electron theory, oxidation is a process in which an element loses electrons. In a narrow sense, oxidation means the chemical addition of oxygen to a substance.
Oxidation number / valence	The electrical charge of a central atom in a coordination compound if all electron pairs and ligands were removed.
Oxidation process	Any method of sewage treatment for the oxidation of the decomposable organic matter that brings about the decomposition of such matter. The usual methods are biological filtration, and activated sludge processes.
Oxidation reaction	A reaction where a substance loses electrons.
Oxidation state	The difference between the number of electrons in an atom in a compound compared with the number of electrons in a neutral atom of the element.
Oxidation-reduction-reaction	A reaction involving the transfer of electrons.
Oxide	An ion of oxygen with an oxidation state equal to 2 (e.g., iron oxide).
Oxidizer	A reactant that removes electrons from another reactant in a redox reaction.
Oxidizing agent	An oxidizer; a reactant that removes electrons from another reactant.
Oxoacid	When one or more hydroxide (OH) groups are bonded to a central atom.
Oxyanion	An anion that contains the element oxygen.
Oxygenate	Liquid organic compounds that can be blended into gasoline to increase its oxygen content; during combustion, this additional oxygen reduces the output of CO and may reduce emissions of ozone-forming materials. The two major oxygenates in use today are ethanol and MTBE.
Ozone	Oxygen in molecular form with three atoms of oxygen forming each molecule (O3). Atmospheric oxygen is molecular in form but each molecule contains only two atoms of oxygen. Ozone is formed by passing high voltage electric charges through dry air. The third atom of oxygen in each molecule of ozone is loosely bound and is easily released, thus making it a powerful oxidant; used to purify water and treat industrial wastes.
Ozone layer	An atmosphere layer at about 20 to 30 miles high (32 to 48 km), normally characterized by high ozone content, which blocks most solar UV radiation from entering the lower atmosphere.

P

Paramagnetism	Property of material characterized by being attracted to a magnetic field.
Parent atom	Atom that undergoes radioactive decay, resulting in one or more daughter atoms.
Parent isotope	An element that undergoes nuclear decay.
Parent nuclide	Nuclide that decays into a specific daughter nuclide during radioactive decay.
Partial pressure	The pressure a gas in a mixture of gases would exert if it occupied the volume by itself, at the same temperature.
Particle	Small portion of matter.
Particulate	Small distinct solids suspended in a gas or liquid.
Parts per million (ppm)	The unit commonly used to represent the degree of pollutant concentration where the concentrations are small. Larger concentrations are given in percentages. 1ppm = 1mg/L. In BOD analysis, the results are expressed in ppm, whereas in the suspended solids test, the values are expressed in percents. In air, ppm is usually a volume/volume ratio; in water, ppm represents a weight/volume ratio.
Pascal (Pa)	SI unit of pressure equal to the force of 1 Newton per square meter.
Pathogenic bacteria	Bacteria which may cause disease in the organisms by their parasitic growth.
Pauli exclusion principle	Principle that says no two electrons or other fermions can have identical quantum numbers in the same atom or molecule.
Pearlizer	A substance, such as glycol distearate (EGDS), which, when added to a formulation, imparts an opalescent finish to that formulation.
Peptide	A small polymer of amino acids, formed by the condensation copolymerization of several amino acids.
Percent composition	Expresses the mass ratio between different elements in a compound.
Percent yield	The percentage of yield that occurred versus the theoretical yield.
Percentage composition	Can be found by totaling the atomic masses of the atoms in the formula, dividing each mass by the total, and changing the results to %-age.
Period	A series of elements, arranged in order of atomic number represented by a horizontal row on the Periodic Table.
Periodic law	Law that states the properties of elements recur in a predictable and systematic way when they are arranged by increasing atomic number.
Periodic table	A table in which the elements are commonly arranged in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding eight families or groups of elements. Within each group there is a gradation of chemical and physical properties, but in general a similarity of chemical behavior. From group to group, however, there is a progressive shift of chemical behavior from one end of the table to the other.
Periodic trend	Regular variation in the properties of elements with increasing atomic number.
Periodicity	Recurring variations in element properties with increasing atomic number due to trends in atomic structure.
Periplanar	Describes two atoms or groups of atoms in the same plane as each other with respect to a single bond.
Peroxide	A polyatomic anion with molecular formula O22-.
Petroleum	Crude oil; natural flammable hydrocarbon mixture found in geologic formations.
pH	A measure of the acidity or basicity of a solution. Mathematically the pH is -log10 of the hydrogen ion concentration of the solution. Under normal circumstances, the possible range of values is 0 -14. A pH < 7 indicates acidity, > 7 indicates basicity. pH is a common specification for water soluble materials.
pH adjustment	A means of maintaining the optimum pH through the use of chemical additives.
pH indicator	Compound that changes color over a range of pH values.
pH meter	Instrument that measure pH of a solution based on the voltage between two electrodes in the solution.
Pharmacology	The science of drugs; the properties of drugs related to their therapeutic effects.
Phase change	Change in the state of matter of a sample (e.g., liquid to vapor).
Phase diagram	Chart showing the phase of a substance according to temperature and pressure.
Phase	Distinct form of matter with uniform chemical and physical properties.
Phenolphthalein alkalinity	a measure of the hydroxides plus one-half of the normal carbonates in aqueous suspension. Measured by the amount of sulfuric acid required to bring the water to a pH value of 8.3, as indicated by a change in color of phenolphthalein. It is expressed in ppm of calcium carbonate (CaCO3).
Phenolphthalein	An organic pH indicator, C20H14O4.
Phentermine	Amphetamine-like component of fen-phen that increases metabolism by raising the body's levels of dopamine and norepinephrine.
Phlogiston	Phlogiston was believed to be a substance all combustible matter contained and released when burned. Phlogiston theory was an early chemical theory to explain the process of oxidation. Phlogiston had no odor, taste, color or mass. Deflogisticated substances were called the calx of the substance.
Phosphorescence	Luminescence produced when electromagnetic energy (usually UV light) kicks an electron from a lower to higher energy state. A photon is released when the electron falls to a lower state.
Photoelectric effect	The emission of electrons from metal when the metal is struck by light.
Photon	Massless packet of energy, which behaves like both a wave and a particle.
Photosynthesis	Process in which water and carbon dioxide are combined in the presence of sunlight to produce glucose and oxygen.This is the process used by green plants to create their food.
Physical change	Change that alters the form of matter but not its chemical composition.
Physical property	Properties of a substance that can be observed without using a chemical reaction that would change the substance.
Phytoplankton	Algae, microscopic single-celled plants that float in the surface waters of the sea, lakes and rivers. In the ocean they constitute the bottom of the marine food chain. They have been called the pasture of the sea. Like plants on land, they use sunlight to convert carbondioxide and water into sugars and oxygen in the process of photosynthesis.
Phytoremediation	Using plants to clear toxic metals from the environment by chelation.
Pi bond	covalent bond formed between two neighbor atom unbonded pi orbitals.
pKa	Negative base 10 log of the acid dissociation constant; lower pKa correlates to stronger acid
pKb	Negative base 10 log of the base dissociation constant; lower pKa correlates with stronger base.
Planck	Planck contributed to the understanding of the electromagnetic spectrum by realizing that the relationship between the change in energy and frequency is quantized according to the equation ∇ E=hv where h is Planck's constant.
Planck's constant	proportionality constant that relates photon energy to frequency; 6.626 x 10-34 J·sec.
Plasma	State of matter with no defined shape or volume consisting of ions and electrons.
Pnictogen	Member of the nitrogen element group.
pOH	Measures the basicity of a solution. It is the negative log of the concentration of the hydroxide ions.
Polar bond	Type of covalent bond in which the electrons are unequally shared between the atoms.
Polar molecule	Molecule containing polar bonds such that the sum of the bond dipole moments is not zero.
Polarizability	Indication of the ease of distortion of an electron cloud around at atom.Large atoms (like iodine) have many electrons, and their location may easily shift, producing regions of partial positive and negative charge.The larger the atom, the greater the polarizability, or the more easily an electron cloud may be distorted.
Pollutant	A substance that contaminates an environment.
Polyatomic ion	Ion comprised of two or more atoms.
Polycarbonate	A polymer in which the repeating unit is an organic carbonate [-R-O-C(O)-O-]n.
Polymer	Molecules which are composed of linked repeating units (called monomers) are referred to as polymers. Polymers are the basis for many plastics and synthetic fibers such as Teflon and polyester.
Polynuclear aromatic hydrocarbon	Hydrocarbon made of fused aromatic rings.
Polyprotic acid	Acid able to donate more than one hydrogen atom or proton per molecule in an aqueous solution.
Porosity	The ratio of the size of a material's pores to the volume of the material's mass.
Positron	The antimatter counterpart to an electron, which has a charge of +1.
Potable water	Water suitable for drinking or cooking purposes from both health and aesthetic considerations.
Potential difference	Work required to move an electric charge from one point to another.
Potential energy	The energy an object has because of its composition or position.
PPB	Parts per billion
PPM	Parts per million
Prechlorination	Chlorination of water prior to filtration, or chlorination of sewage prior to treatment.
Precipitant	A chemical or chemicals that cause a precipitate to form when added to a solution.
Precipitate	To form an insoluble compound by reacting salts or altering a compound's solubility.
Precipitation reaction	Chemical reaction between two soluble salts in which one product is an insoluble salt.
Precision	The agreement of repeated measurements with each other.
Precursor	In metabolism, a chemical substance from which another chemical substance is formed
Preservative	A chemical added to a product to inhibit the growth of bacteria.
Pressure	Measure of force per unit area.
Pretreatment	Any wastewater treatment process used to partially reduce pollution load before the wastewater is introduced into a main sewer system or delivered to a treatment plant; a substantial reduction of the pollution load.
Primary standard	Very pure reagent.
Principal energy level	Primary energy signature of an electron, indicated by quantum number n.
Principal quantum number	The number related to the amount of energy an electron has and therefore describing which shell the electron is in.
Product	Substance formed as a result of a chemical reaction.
Proof	Volume percentage of ethyl alcohol in an alcoholic beverage.
Property	A characteristic of matter such as color, density, brittleness, etc..
Proportion	An equality between two ratios.
Protecting group	A ground used in preventing undesired reactions.
Protein	A biological polymer formed by condensation reactions among a set of 20 different amino acids.
Proton	Particle found in a nucleus with a positive charge. Number of these gives atomic number.
Protonated	Having acquired an additional proton (H+).
Protonation	Addition of a proton to an atom, ion, or molecule.
PSI	Unit of pressure; pounds per square inch.
Pure substance	Sample of matter with constant composition and distinct chemical properties.
Putrefaction	Biological decomposition of organic matter accompanied by the production of a foul smell associated with anaerobic condition.

Q

Qualitative analysis	Determination of the chemical composition of a sample
Quanta	Plural of quantum.
Quantitative analysis	Chemical determination of the amounts or proportions of constituents in a substance.
Quantum	A discrete packet of matter or energy, plural is quanta
Quantum number	Value used to describe the energy levels of atoms or molecules. There are four quantum numbers.
Quartz	An abundant mineral consisting of silicon dioxide(SiO2) with a hardness of 7 on the Mohs' scale.
Quench	Stopping a reaction quickly, first used to refer to harden steel by quickly putting red-hot steel into cold water.
Quicklime	A common name for calcium oxide.

R

Radiant energy	Energy which is transmitted away from its source, for example, energy that is emitted when electrons transition down from one level to another.
Radiation	Emitted energy in the form of rays, waves, or particles.
Radical	A species with an odd number of electrons; formerly called free radical.
Radioactive	Substance containing an element which decays.
Radioactive tracer	Radioactive element or compound added to a material to monitor its progress through a system.
Radioactivity	Spontaneous emission of radiation as particles or photons from a nuclear reaction.
Radioisotope	Contraction for words "radioactive isotope" of an element.
Raoult's Law	Relation that states the vapor pressure of a solution depends on the mole fraction of solute added to the solution.
Ratio	The relative size of two quantities expressed as the quotient of one divided by the other; the ratio of a to b is written as a:b or a/b.
Raw sewage	Sewage prior to receiving any treatment.
Reactant	A starting material in a chemical reaction.
Reaction quotient	Q-ratio of the concentration of products of a reaction to the concentration of the reactants.
Reaction rate	The speed at which chemical reactants form products.
Reaction	A chemical change that forms new substances.
Reactivity	The degree to which a substance will respond to a stimulus or interact with another substance.
Reagent	Compound or mixture added to a system to produce a reaction or test if one occurs.
Real gas	Gas that does not behave as an ideal gas because its molecules interact with one another.
Receptor	Protein molecules on the surface of cell membranes used for communication between cells.
Recorder	A device that makes a graph or other automatic record of the stage, pressure, depth, velocity, or the movement or position of water controlling devices, usually as a function of time.
Rectilinear propagation	The principle that electromagnetic radiations like light travel in straight lines.
Recycling	To treat or process waste materials so as to make them suitable for reuse. The key to successful recycling of materials contained in refuse lies in the separation of recyclable components from the main bulk of the waste.
Redox indicator	Compound that changes color at a specific potential difference.
Redox reaction	Set of chemical reactions involving reduction and oxidation
Redox titration	Titration of reducing agent by an oxidizing agent or vice versa.
Reducing	The gain of electrons by an atom, ion, or molecule.
Reduction	Chemical reaction in which an atom or molecule gains an electron; decrease in positive valence; addition of hydrogen to a molecule.
Reduction reaction	A reaction in which a substance gains at least one electron.
Reduction treatment	The opposite of oxidation treatment wherein a reductant is used to lower the valence state of a pollutant to a less toxic form; e.g. the use of SO2 to reduce Cr6+ to Cr3+ in an acidic solution.
Refrigerant	A chemical used in refrigeration, to keep substances cool.
Regelation	The process of melting ice by pressure. Inasmuch as water expands upon freezing, pressure will reverse the process, forcing water to melt. Then when the pressure is released, the water re-freezes (re-gells).
Relative density	Ratio of density of a substance to the density of water.
Relative error	Uncertainty of a measurement compared to the size of the measurement.
Relative standard deviation	Measure of precision of data, calculated by dividing standard deviation by the average of data values.
Relative uncertainty	Relative error; uncertainty of a measurement compared to the size of the measurement.
Residual chlorine	Chlorine remaining in water or wastewater at the end of specified contact period as combined or free chlorine.
Residue	Matter remaining after evaporation or distillation or an undesirable reaction byproduct or a recognizable portion of a larger molecule.
Resistance	The opposition of a substance to the passage through it of a steady electric current.From Ohm's Law, R = E/I, the resistance equals the voltage of the cell divided by the current flow.
Resistor	A component of an electrical circuit intended to offer resistance to electrical current flow.
Resonance structure	Possible structures of a molecule for which more than one electron-dot structure can be written, which differ in the bond pairs between atoms.
Resonance	Average of two or more Lewis structure, differing in the position of electrons.
Reverse osmosis	Filtration method that works by applying pressure on one side of a semipermeable membrane
Reversible reaction	Chemical reaction in which the products act as reactants for the reverse reaction.
RNA	Ribonucleic acid, a molecule which codes for amino acid sequences.
Roasting	Metallurgical process in which a sulfide ore is heated in air to form a free metal or metal oxide.
Room temperature	Temperature that is comfortable for humans, typically around 300 K.
RT	Abbreviation for room temperature; ambient temperature that is comfortable for humans.
Rust preventative	A compound or formulated system used for coating metal surfaces to produce a film which protects against rust formation

S

Saccharin	A compound, C7H5NO3S, that is several hundred times sweeter than cane sugar and is used as a calorie-free sweetener.
Salinity	(1) The relative concentration of salts, usually sodium chloride, in a given water. It is usually expressed in terms of the number of ppm of chloride. (2) A measure of the concentration of dissolved mineral substances in water.
Salt	Any compound formed by combination of any negative ion (except hydroxide) with any positive ion (except hydrogen or hydronium); the precipitate produced as the result of neutralization of an acid with a base.
Salt bridge	Connection containing a weak electrolyte located between the oxidation and reduction half cells of a galvanic cell.
Salt thickening	The increase in viscosity of a micellar solution on the addition of an electrolyte, such as sodium chloride. This is a similar effect to that seen with THICKENERS, but by a different mechanism.
Saponification	Reaction between triglycerides and either sodium hydroxide or potassium hydroxide to form a fatty acid salt called soap and glycerol.
Saturated	(1) In organics, a chemical compound with all carbon bonds satisfied; it does not contain double or triple bonds and thus cannot add elements or compounds. (2) In liquids, a solution that contains enough of a dissolved solid, liquid, or gas so that no more will dissolve into the solution at a given temperature and pressure.
Saturated fat	Lipid containing only single C-C bonds.
Saturated solution	Chemical solution containing the maximum concentration of dissolved solute for that temperature.
Scale	The precipitate that forms on surfaces in contact with water as the results of a physical or chemical change, often due to the presence of calcium carbonate (CaCO3) or magnesium carbonate (MgCO3).
Schroedinger's wave equation	Explains the shapes of the orbitals of the electrons around an atom. They are probability distributions. That is, there is a probability of finding an electron's position in a "cloud" around an atomic nucleus. The electron appears to be "spread out" as it orbits, filling its cloud.
Scientific law	General rule that explains a body of observations in the form of a mathematical or verbal statement and implies a cause an effect relationship between observations.
Scientific method	System of acquiring knowledge and solving problems through observation and experimental testing of hypotheses.
Second quantum number	ℓ, the quantum number associated with the angular momentum of an atomic electron.
Sedimentation	The deposition of suspended matter carried by water, wastewater, or other liquids, by gravity. It is usually accomplished by reducing the velocity of the liquid below the point at which it can transport the suspended material. Also called settling.
Semi-metal	Element with a partially filled p orbital, causing it to exhibit properties intermediate between those of metals and nonmetals.
Settleable solids	Particles of debris and fine matter heavy enough to settle out of wastewater.
Settled sewage	Sewage from which most of the settleable solids have been removed by sedimentation.
Sewage	The total of organic waste and wastewater generated by residential and commercial establishments.
Shell	Where the electrons generally are. These shells are composed of 4 types of electron subshells: s, p, d and f subshells.
SI Unit	Stands for Systeme International d'Unites, a international system which established a uniform set of measurement units.
SI	System Internationale, the standard metric system of units.
Sigma bond	Covalent bonds formed by overlapping of outer orbitals of adjacent atoms.
Significant digit	Those that can be accurately measured. An answer can have no more significant digits than the least number of them in the data.
Silica	Silica is the common name for silicon dioxide, SiO2.It exists in nature as crystalline quartz.
Simplest formula	Ratio of elements in a compound.
Single bond	When an electron pair is shared by two atoms.
Single displacement reaction	Chemical reaction in which an ion of one reactant is exchanged for the corresponding ion of another reactant.
Size of atom	Can be measured by oil slick experiments or by calculating how many atoms lie along the side of a cube of a known number of moles of atoms.
Size of nucleus	Was measured by Lord Rutherford using the scattering patterns of alpha particles passing through gold foil. It is 10-15 meter.
Skeletal structure	Two-dimensional graphic representation of atoms and bonds in a molecule using element symbols and solid lines for bonds.
Sludge	The solids (and accompanying water and organic matter) which are separated from sewage or industrial wastewater in treatment plant facilities. Sludge separation and disposal is one of the major expenses in wastewater treatment operations.
Sludge conditioning	A process employed to prepare sludge for final disposal, e.g., thickening, digesting, heat treatment or other procedures.
Sludge digestion	The process by which organic or volatile matter in sludge is gasified, liquefied, mineralized, or converted into more stable organic matter through the activities of either anaerobic or aerobic organisms.
Sludge disposal	The final disposal of solid wastes including the use of sewage sludge as fertilizers and soil builders, and fill for low-lying lands.
Sludge thickening	The increase in solids concentrations of sludge in the sedimentation of digestion tank.
Slurry	A watery mixture or suspension of solids.
Smog	A fog containing fumes, or a photochemical haze caused by the action of ultraviolet radiation on hydrocarbons and NOx from automobile exhaust.
Soda ash	A common water treating chemical, sodium carbonate.
Softening	the removal of hardness—calcium and magnesium—from water.
Soil	In the surfactant world - any material, solid, liquid or paste contaminant adsorbed onto a substrate.
Sol	A liquid colloidal dispersion; a fluid colloidal system in which solid particles are dispersed in a liquid colloidal solution.
Solder	An alloy of lead/tin used for making permanent electrical connections between parts and wire.
Solid	State of matter characterized by high degree of organization, with a stable shape and volume.
Solidification	Phase change that results in formation of a solid.
Solubility	The maximum amount of a substance that will dissolve in a given amount of solvent at a given temperature.
Solubility product	Ksp, the equilibrium constant for a chemical reaction in which a solid ionic compound dissolves to yield its ions in solution.
Soluble oil	An oil that readily forms a stable emulsion or colloidal suspension in water.
Solute	The substance (solid, liquid, or gas) dissolved in a solution, for example, the salt in saltwater.
Solution	A mixture of two or more in which two or more materials are dissolved in another material.
Solvent	The substance present in the largest amount in a solution; often the liquid component.
Sound	A disturbance that travels through air, land, water that can be heard.
Specific gravity	A comparison by weight to an equal volume of pure water, at a standard temperature.
Specific heat	The amount of heat it takes for a substance to be raised 1°C.
Specific heat capacity	Amount of heat needed to raise the temperature of a substance per unit mass.
Spectator ion	Ion found in the same amount on both the reactant and product sides of a chemical reaction that does not affect equilibrium.
Spectrometer	An instrument for measuring the emission or absorption of light of a particular wavelength.
Spectrophotometer	Tool that measures the absorption or emission of electromagnetic radiation.
spectroscopy	The science that deals with the use of the spectroscope and with spectrum analysis.A spectroscope is an optical device for producing and observing a spectrum of light or radiation from any source.
Spectrum	Characteristic wavelengths of electromagnetic radiation emitted or absorbed by an object or substance.
Spin	The spin of an electron is designated by ms, the electron spin quantum number, which can have values of +1/2 and -1/2.In the presence of an external magnetic field an electron in an orbital can have one of two possible energy states, which depend on whether the magnetic field associated with the electron is aligned with or against the external magnetic field.
Spin quantum number (Ms)	Fourth quantum number, which indicated orientation of intrinsic angular momentum of an electron in an atom.
Spontaneous fission	Spontaneous splitting of an atomic nucleus into two smaller nuclei and usually neutrons, accompanied by the release of energy.
Spontaneous process	Process which can occur without any energy input from the surroundings.
Spontaneous reaction	A reaction that will proceed without any outside energy.
Spontaneous change	Changes that occur on their own.
Standard hydrogen electrode	SHE, the standard measurement of electrode potential for the thermodynamic scale of redox potentials.
Standard oxidation potential	Potential in volts generated by an oxidation half-reaction compared to the standard hydrogen electrode at 25 °C, 1 atm pressure and a concentration of 1 M.
Standard reduction potential	Potential in volts generated by a reduction half-reaction compared to the standard hydrogen electrode at 25 °C, 1 atm pressure and a concentration of 1 M.
Standard solution	A solution with a precisely known concentration.
Standard temperature and pressure	STP, 273 K (0° Celsius or 32° Fahrenheit) and 1 atm pressure.
Standard	Reference used to calibrate measurements.
Standardized solution	A solution containing a known, precise concentration of an element or chemical compound, often used to calibrate analytical chemistry measurement devices.
State of matter	Homogeneous phase of matter (e.g., solid, liquid).
State property	A state property is a quantity that is independent of how the substance was prepared. Examples of state properties are altitude, pressure, volume, temperature and internal energy.
States of matter	Solid, liquid, gas and plasma. Plasma is a "soup" of disassociated nuclei and electrons, normally found only in stellar objects.
Steam distillation	Distillation process in which steam or water is added to lower boiling points of compounds.
Steel	An alloy of iron that contains carbon.
Stereochemistry	The spatial arrangement of atoms in molecules or compounds and the relation of spatial arrangement to the substanceis properties.
Stereoisomer	Two or more compounds with the same molecular formula and the same atom-to-atom arrangement, but with different arrangement of atoms in space. stereoisomeric (adjective)
Steric number	Number of atoms bonded to a central atom of an molecule plus number of lone electron pairs attached to the central atom.
Steroid	Compounds containing a 17-carbon, four-ring system.
Stock solution	Concentrated solution intended to be diluted to a lower concentration for actual use.
Stoichiometry	The study of the relationships between amounts of products and reactants.
Storm sewage	Liquid flowing in sewers during or following a period of heavy rainfall.
STP	Standard temperature and pressure. This is 0°C and 1 atm.
Stratosphere	The layer of the earth's atmosphere that extends from roughly 7 miles (11 km) above the surface to 31 miles (50 km) above the surface.
Strong acid	Acid that completely dissociates into its ions in aqueous solution.
Strong base	Base that completely dissociates into its ions in aqueous solution (e.g., NaOH).
Strong electrolyte	Electrolyte that completely dissociates in aqueous solution.
Sublimation	The direct conversion of a solid to a gas.
Subshell	Subdivision of electron shells separated by electron orbitals (e.g., s, p, d, f).
Substituent	Atom or functional group that replaces a hydrogen atom in a hydrocarbon.
Substitution reaction	Chemical reaction in which a functional group or atom is replaced by another functional group or atom.
Substrate	Medium on which a reaction occurs or reagent that offers a surface for absorption.
Sulfation	The process by which an alcohol, such as lauryl alcohol, is reacted with sulfur trioxide (or chlorosulfonic acid) to give an alkyl sulfuric acid.
Sulfonation	The process by which a material such as an alkylate is reacted with sulfur trioxide to give a sulfonic acid.
Superconductivity	A state in which the electrical resistance of a material is so low that it cannot be measured and appears to be zero.The superconducting state is also characterized by unusual magnetic properties.
Supercritical	Above the critical point; above critical temperature or pressure.
Supernate	The liquid result of a precipitation reaction.
Supersaturated solution	A solution that temporarily contains more solute than the saturated amount at some temperature.
Supersaturated	Supercooled; condition in which a liquid has been cooled to a temperature below which crystallization normally occurs, yet without solid formation.
Surface tension	The property, due to molecular forces in the surface film, that tends to contract the liquid into a form having the least surface/volume ratio.
Surfactant	A surface-active substance, such as a detergent or soap, that lowers the surface tension of a solvent (usually water).
Suspended matter	(1) Solids in suspension in water, wastewater or effluent. (2) Solids in suspension that can be removed readily by standard filtering procedures in a laboratory.
Suspended solid	(1) Solids that either float on the surface of, or are in suspension in, water, wastewater, or other liquids, and which are largely removable by laboratory filtering. (2) The quantity of material removed from wastewater in a laboratory test, as prescribed in “Standard Methods” and referred to as nonfilterable residue.
Suspension	Heterogeneous mixture of solid particles in a fluid.
Synthesis	Describes when a molecule consists of two or more smaller ones.
Synthesis reaction	Direct combination reaction; chemical reaction in which two or more species combine to form a more complex product.

T

Taxol	A naturally occurring compound (extracted from the bark of the Pacific yew tree) that has been approved by the U.S. Food and Drug Administration (FDA) for treating advanced breast or ovarian cancers.
Temperature	Measure of how warm or cold a substance is.
Tensile strength	The resistance of a substance to any force used to tear it apart.
Teratogen	A substance that causes fetal abnormalities.
Term	Each compound or element in a chemical equation.
Tertiary treatment	Process utilized to remove practically all solids and organic matter from wastewater. Granular activated carbon filtration is a tertiary treatment process. Phosphate removal by chemical coagulation is also regarded as a step in tertiary treatment.
Tetrahedral	Molecular geometry in which a central atom form four bonds directed toward the corners of a regular tetrahedron.
Texas carbon	A carbon atom that forms five covalent bonds, forming a structure resembling a star.
Theoretical yield	Quantity of product that would be obtained if the limiting reactant in a reaction reacted completely.
Theory	A principle that explains a body of facts and the laws based on them.
Thermionic emission	The boiling off of electrons from heated metals. It gives a source of electrons for cathode ray tubes.
Thermistor	A semiconductor whose resistance will vary with temperature.
Thermodynamics	The study of temperature, pressure, volume, and energy flow in chemical reactions.
Thermosetting plastic	A polymer that is made irreversibly rigid upon heating.
Thickener	A substance, such as Xanthan Gum, which, when added in low concentrations to a fluid, raises the viscosity of that fluid. (see also SALT THICKENING).
Thiol group	Functional group containing a sulfur bound to a hydrogen, -SH.
Thiol	An organic sulfur compound consisting of an alkyl or aryl group and a sulfur-hydrogen group; R-SH.
Tincture	An extract of a sample into a solution, usually with alcohol as the solvent.
Titrant	Solution of known concentration used in a titration to determine the concentration of a second solution.
Titration	A method of analyzing the composition of a solution by adding known amounts of a standardized solution until a given reaction (color change, precipitation, or conductivity change) is produced.
Torr	Unit of pressure equal to 1 mm Hg or 1/760 standard atmospheric pressure.
Toxicity	The degree to which a substance is poisonous.
Tracer	(1) A foreign substance mixed with or attached to a given substance for the determination of the location or distribution of the substance. (2) An element or compound that has been made radioactive so that it can be easily followed (traced) in biological and industrial processes. Radiation emitted by the radioisotope pinpoints its location.
Trans isomer	Isomer in which functional groups occur on opposite sides of the double bond.
Transition interval	Concentration range of chemical species that can be detected using an indicator.
Transition metal	Element from the B group of the periodic table characterized by having partially filled d electron orbital sublevels.
Translational energy	Energy of motion through space.
Transmute	To change from one form or substance into another.
Treatment efficiency	Usually refers to the percentage reduction of a specific or group of pollutants by a specific wastewater treatment step or treatment plant.
Triad	A group of three elements whose chemical and physical properties aresomewhat related.
Triple point	Temperature and pressure at which the solid, liquid, and vapor phase of a substance coexist at equilibrium with each other.
Tritium	A rare isotope of hydrogen with one proton and two neutrons.
Troposphere	The lowest part of the earth's atmosphere, extending from the surface of the planet to the bottom of the stratosphere.
Turbidimeter	An instrument for measurement of turbidity in which a standard suspension is used for reference.
Turbidity	(1) A condition in water or wastewater caused by the presence of suspended matter, resulting in the scattering and absorption of light rays. (2) A measure of fine suspended matter in liquids. (3) An analytical quantity usually reported in turbidity units (NTU/FNU, FTU, JTU) determined by measurements of light diffraction.
Tyndall effect	The scattering of a beam of light as is passes through a colloid.

U

Ultraviolet radiation	Ionizing electromagnetic radiation with a wavelength between 100 nm and 400 nm. Sometimes called black light.
UN ID	A four-digit code used to identify dangerous or flammable chemicals. United Nations Identifier
UN number	A UN ID used for the transport of dangerous materials.
Unit	A set magnitude of measurements used to express a certain type of physical quantity such as length, mass, and time. The SI units replaced previous used system of units for scientific purposes.
Unit cell	The smallest part of a crystal that could be used to create the whole crystal.
Universal gas constant	Usually indicated by R, the gas constant is the Boltzmann constant in units of energy per temperature per mole: R = 8.3145 J/mol·K
Universal indicator	A mixture of pH indicators used to measure pH over a wide range of values.
Universal solvent	A chemical that dissolves most substances. While water is often called the universal solvent, most nonpolar molecules are insoluble in it.
Unreacted (oil)	Unreacted is an organic substance present in small amounts in products generally consisting of sulf(on)ation feedstock, for example an alkylate or fatty alcohol or reaction by-products, for example, sulfones.
Unsaturated	Any chemical compound with more than one bond between adjacent atoms, usually carbon, and thus reactive toward the addition of other atoms at that point; for example: olefins, diolefins, and unsaturated fatty acids.
Unsaturated fat	A lipid that contains no carbon-carbon double bonds.
Unsaturated solution	A solution in which solute concentration is lower than its solubility. All solute present dissolves into the solution.
Unsulfated matter	see - UNREACTED

V

Vacuum	A volume containing little to no matter (no pressure).
Valence	The relative ability of a biological substance to react or combine; a positive number that characterizes the combining power of an element for other elements, as measured by the number of bonds to other atoms which one atom of the given element forms upon chemical combination – hydrogen is assigned valence 1, and the valence is the number of hydrogen atoms, or their equivalent, with which an atom of the given element combines.
Valence bond theory	Explanation of bonding between two atoms as a result of the overlap of half-filled atomic orbitals.
Valence electron	Outer electron most likely to participate in bond formation or a chemical reaction.
Valence shell electron pair repulsion theory	Molecular model that predicts geometry of atoms in a molecule by minimizing electrostatic forces between valence electrons around a central atom.
Van der Waals equation	An equation for non-ideal gasses that accounts for intermolecular attraction and the volumes occupied by the gas molecules.
Van der Waals force	Weak interactions between molecules. These weak forces are caused by the attraction between protons in one molecule and electrons in an adjacent molecule. Because of the greater distance between the particles in one molecule and another, Van der waals forces are only 1/100 as strong as the covalent bond.
Van der Waals radius	Half the distance between two unbonded atoms in a state of electrostatic balance.
Vapor	Another name for a gas.
Vapor pressure	Pressure exerted by a vapor in equilibrium with liquid or solid phases of the same substance or the partial pressure of a vapor above its liquid or solid.
Vaporization	Phase transition from the liquid phase to gas phase.
Vector	A geometric object that has both magnitude and direction.
Velocity	Speed of an object; the change in position over time.
Venting	Providing an opening for the discharge of gases or the relief of pressure.
Viscosity	The resistance offered by a fluid (liquid or gas) to flow. The viscosity is a characteristic property and is a measure of the combined effects of adhesion and cohesion.
Viscosity index	The relationship of viscosity to temperature of a fluid. High viscosity index fluids will display less change in viscosity with temperature.
Visible light	Electromagnetic radiation that can be perceived by the human eye, usually from 380 nm to 750 nm (400 to 700 nm).
Volatile	A substance which is easily vaporized.
Volatile solid	The quantity of solid in water, wastewater or other liquids, lost on ignition of the dry solids at 600 °C.
Volatize	To make volatile; to cause to pass off in vapor.
Volt	A unit of electrical potential.
Voltage	The electrical pressure (electromotive force) that makes current flow through a conductor.
Volume	The space occupied in three dimensions.
Volumetric flask	Type of chemistry glassware used to prepare solutions of known concentration.
VSEPR	see Valence Shell Electron Pair Repulsion Theory
Vulcanization	The process for changing rubber from a weak material into a hard, strong material, usually by heating with sulfur.

W

Washdown	Water resulting from cleaning of equipment, walls, floors, etc., within a plant.
Water gas	A combustion fuel that contains hydrogen gas and carbon monoxide.
Water of crystallization	Water the stoichiometrically bound in a crystal.
Water of hydration	Water stoichiometrically bound in a compound, forming a hydrate.
Water	A compound formed by one oxygen atom and two hydrogen atoms. Usually this refers to the liquid form of the molecule.
Watt	The practical unit of electrical power.
Wave	A signal which propagates through space, much like a water wave moves through water.
Wavefunction	A function that describes the probability of the quantum state of a particle in terms of spin, time, position, and/or momentum.
Wavelength	The distance between any two identical points in consecutive cycles of a wave.Often measured from peak to peak or crest to crest. Symbolized by the Greek letter lambda.
Wave-particle duality	The concept that photons and subatomic particles exhibit properties of both waves and particles.
Wax	A lipid consisting of chains of esters or alkanes derived from fatty acids and alcohols.
Weak acid	Substances capable of donating hydrogen but do not completely ionize in solution.
Weak base	Substances capable of accepting hydrogen but do not completely ionize in solution.
Weak electrolyte	An electrolyte that does not completely dissociate into its ions in water.
wedge-and-dash projection	Molecule representation using three types of lines to show three-dimensional structure.
Weight	The measures of the earth's gravitational pull on a object.
Wetting	The coating of a contact surface with an adherent film of liquid.
Wire gauge	Wire size, measured in diameter.
Word equation	A chemical equation expressed in words rather than chemical formulas.
Work	Force multiplied by distance or the amount of energy needed to move a mass against a force.
Working solution	A chemical solution prepared for use in a lab, usually by diluting a stock solution.
Writing and Balancing	Starting Materials and Products have the same kinds of elements and same numbers of atoms.

X

X-ray	Electromagnetic radiation of high frequency and short wavelength (ranging from 10-11 to 10-9 meters).
X-ray crystallography	A technique of determining a molecule's three-dimensional structure by analyzing the X-ray diffraction patterns of crystals made up of the molecule in question.

Y

Yield	In chemistry, yield refers to the quantity of a product obtained from a chemical reaction. Chemists refer to experimental yield, actual yield, theoretical yield, and percent yield to differentiate between calculated yield values and those actually obtained from a reaction.
Yoctomole (ymol)	10-24 moles; A single molecule corresponds to 1/Avogadro's number, or 1.66 X 10-24 moles, or 1.66 ymol.

Z

Zaitsev rule	Rule in organic chemistry that states alkene formation from an elimination reaction will produce more highly substituted alkenes.
Zeolite	A natural or synthetic hydrated aluminosilicate with an open three-dimensional crystal structure which water molecules are held in cavities in the lattice. They are used to soften water.
Zeolite process	An ion-exchange process for softening water. The zeolite exchanges sodium ions for hardness constituents (calcium, magnesium, etc.) in the water.
Zeta potential (ζ-potential)	The potential difference across the phase boundary between a liquid and a solid.
Zwitterion	An ion that has a positive and negative charge on the same group of atoms. It is also called dipolar ion.
Zymogen	An inactive biomolecule that is a precursor to an enzyme.