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Home > Resources > Technical Information > Chemical Glossary
Chemical Glossary


Absolute alcoholCommon name for high purity ethanol or ethyl alcohol.
Absolute errorExpression of the uncertainty or inaccuracy of a measurement.
Absolute temperatureTemperature measured using the Kelvin scale.
Absolute uncertaintyThe 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.
AbsorbanceMeasure of the amount of light absorbed by a sample.
Absorption spectroscopyTechnique used to determine concentration and structure of a sample based on which wavelengths of light are absorbed.
Absorption spectrumGraph of amount of absorption as a function of wavelength.
AbsorptionThe take up of a gas/light by a solid or liquid
AbsorptivityAbsorption cross section of extinction coefficient, which is the absorbance of a solution per unit path length and concentration.
AccuracyThe closeness of a measurement to a true or accepted value.
AchiralDescribes any molecule or object that is superimposable upon its mirror image.
Acid anhydrideA nonmetal oxide that reacts with water to form an acidic solution.
Acid dissociation constantKa - a quantitative measure of how strong an acid is.
AcidA chemical species that accepts electrons or donate protons or hydrogen ions.
Acid-base indicatorA weak acid or weak base that changes color when the concentration of hydrogen or hydroxide ions changes in an aqueous solution.
Acid-base titrationA procedure to find the concentration of an acid or base by reacting a known concentration with the unknown until the equivalence point is reached.
AcidicDescribes a solution with a relatively high concentration of H+ ions.
Acidic solutionAn aqueous solution with a pH less than 7.0.
AcidificationThe process of increasing the hydrogen ion concentration.
AcidityThe 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.
ActinidesUsually, the actinides are considered to be elements 90 (thorium) through 103 (lawrencium). Otherwise, the actinides are defined according to their common properties.
ActiniumThe name for the element with atomic number 89 and is represented by the symbol Ac. It is a member of the actinide group.
Activated complexAn 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 processRemoves organic matter from sewage by saturating it with air and microbial organisms.
ActivationTreatment of a substance by heat, radiation, or activating reagent to produce a more complete or rapid chemical or physical change.
Activation energyEa - the minimum amount of energy needed for a chemical reaction to occur.
Active transportThe movement of molecules or ions from a region of lower concentration to higher concentration; requires energy
Activity seriesList of metals ranked in order of decreasing activity, used to predict which metals displace others in aqueous solutions.
Actual yieldThe quantity of product experimentally obtained from a chemical reaction.
Acute health effectThe effect caused by initial exposure to a chemical.
Acyl groupA functional group with the formula RCO- , where R is bound to carbon via a single bond.
AdditiveAny material added to a base stock to change its properties, characteristics or performance.
AdhesionThe force or attraction that holds two separate objects together.
AdsorptionThe 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.
AdulterantA chemical that acts as a contaminant in the context of another substance's purity.
Advanced waste treatmentAny 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.
AerobicLiving or occurring only in the presence of oxygen.
Aerobic biological oxidationAny 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.
AerogelA 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.
AetherA medium believed to carry light waves in the 18th and 19th century.
AirThe mixture of gases that make up the Earth's atmosphere, consisting mainly of nitrogen, with oxygen, water vapor, argon, and carbon dioxide.
AlchemySeveral 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.
alcogelA 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.
AlcoholAny class of organic compounds containing the hydroxyl group, OH. Specifically, the term is applied to ethyl alcohol (C2H5OH).
AlgaecideChemical agent added to water to destroy algae.
Aliphatic amino acidAmino acid that has an aliphatic side chain.
Aliphatic compoundAn organic compound containing carbon and hydrogen joined into straight chains, branches chains, or non-aromatic rings.
Aliphatic hydrocarbonA hydrocarbon containing carbon and hydrogen joined into straight chains, branches chains, or non-aromatic rings.
Alkali metalAny element found in group IA (first column) of the periodic table.
AlkalineDescribes an alkali (basic) or a solution that has excess of hydroxide ions.
AlkalinityThe 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).
AlkaneA saturated hydrocarbon with the general formula CnH2n+2.
AlkanolamineAn amine where some or all of the alkyl groups attached to the nitrogen contain hydroxyl functionality. For example; triethanolamine (TEA), monisopropanolamine (MIPA).
AlkeneA hydrocarbon containing a double carbon-carbon bond.
Alkenyl groupThe hydrocarbon group formed when a hydrogen atom is removed from an alkene group.
AlkoxideAn 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 groupFunctional group containing an alkyl group bonded to oxygen.
AlkylateThe 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.
AlkylatedA 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.
AlloyA combination of metals usually made to produce a metal with stronger properties of both.
Alpha decaySpontaneous radioactive decay which produces an alpha particle or helium nucleus.
Alpha particleHelium nuclei (no electrons) produced in nuclear reactions. They are helium ions, He+2.
Alpha radiationThe 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.
AlumTechnically, a double sulfate of ammonium or a univalent or trivalent metal but commonly used to denote aluminum sulfate (Al2(SO4)3.
AmalgamAn alloy of mercury with another metal, often used as a dental filling.
AmideFunctional group containing a carbonyl group linked to a nitrogen atom.
AmineA 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 acidAn organic acid containing a carboxyl (COOH) and amine (NH2) functional group along with a side chain.
AmorphousTerm describing a solid that does not have crystalline structure.
AmphetamineAny of the compounds which are substituted or slightly modified amphetamine molecules.
AmphotericA compound that can act as a base and an acid.
Amphoteric oxideOxide that can act as either an acid or a base in a reaction to produce a salt and water.
Amphoteric surfactantA surfactant in which the hydrophile has both positive and negative charges. Examples; betaines and amine oxides.
AmphotericSubstance capable of acting as either an acid or a base.
AnabolismMetabolic synthesis of proteins, fats and other constituents of living organisms from molecules or simple precursors, which usually requires an input of energy.
AnaerobicLiving or occurring only in the absence of free oxygen.
Anaerobic biological treatmentAny 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.
AnestheticA substance that produces loss of sensation, sometimes with loss of consciousness as well.
AngstromA 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 numberℓ, the quantum number associated with the angular momentum of an electron.
AnhydrousA term meaning without water.
AnionIon having a negative charge; an atom with extra electrons. Atoms of non-metals, in solution, become anions.
Anionic surfactantA surfactant in which the hydrophile is negatively charged. Examples; sulfonates and sulfates.
AnodeA positive electrode; the electrode toward which electrons flow; the electrode at which oxidation occurs.
AnthropogenicResulting from the actions and influence of human beings.
AntiaromaticityThe unusual instability that results from a continuous cyclic system of 4n pi electrons (where n is any integer).
Antibonding orbitalMolecular orbital with an electron outside the region between the two nuclei.
AntifoamAn additive used to suppress the foaming characteristics of a formulation in service.
AntimatterAny 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.
AntimicrobialA chemical which either destroys or inhibits the growth of microscopic and sub-microscopic organisms.
Anti-periplanarPeriplanar conformation where the dihedral atom between atoms is between 150° and 180°.
AntisenseHaving a sequence complementary to a segment of genetic material and serving to inhibit gene function.
Antiwear additiveCompounds 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 regiaMixture of hydrochloric and nitric acids, capable of dissolving gold, platinum, and palladium.
Aqueous solutionA solution in which water is the solvent.
AqueousDescribes a system containing water.
AquiferWater 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 compoundMainly an organic molecule that contains a benzene ring.
AromaticityThe 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 acidSpecies that dissociates in water to form protons or hydrogen ions.
Arrhenius baseSpecies that increases the number of hydroxide ions when added to water.
ArylA functional group derived from a simple aromatic ring when one hydrogen is removed from the ring.
AsteroidAny 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.
AsymmetricMolecules that are not symmetrical.
AtherosclerosisA disease of the arterial walls characterized by fatty deposits and abnormal tissue growth.
AtmosphereUnit of pressure equal to 101325 pascals or 760mmHg. Its symbol is atm.
AtomThe smallest unit of an element which has all the properties of the element. It is composed of protons, neutrons and electrons.
Atomic absorptionQuantitative 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 massThe 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/weightThe 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 numberThe 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 radiusValue used to describe the size of an atom, usually half the distance between two atoms just touching each other.
Atomic solidSolid in which atoms are bonded to other atoms of the same type.
Atomic volumeVolume occupied by one mole of an element at room temperature.
ATPATP is the acronym for the molecule adenosine triphosphate.
Aufbau principleIdea that electrons are added to orbitals as protons are added to an atom.
AusteniteThe face - centered cubic crystalline form of iron.
AutoclaveAn airtight chamber use for processes requiring dry temperatures above 212 degrees F.
AutooxidationOxidation caused by the atmosphere; an oxidation reaction that is self-catalyzed and spontaneous; an oxidation reaction begun only by an inductor.
Avogadro's LawRelation that states equal volumes of all gases contain the same number of molecules at the same pressure and temperature.
Avogadro's numberThe number of particles present in 1 mole of a substance, experimentally determined to be 6.02 x 1023.
AzeotropeA solution that retains its chemical composition when distilled.
Azimuthal quantum numberThe quantum number associated with the angular momentum of an electron, determining the shape of its orbital.
CalibrationThe checking, adjusting, or systematic standardizing of the graduations of a quantitative measuring instrument.
CalorieThe quantity of heat necessary to raise the temperature of 1 gram of water 1 °C at 1 atmosphere pressure.
CalorimeterInstrument designed to measure heat flow of a chemical reaction or physical change.
Canal ray tubeShowed that ions are produced by electron bombardment. The simplest positive ion, H+1, is the PROTON.
Capillary actionThe spontaneous floe of liquid into a narrow tube or porous material.
CarbocyclicBeing or having an organic ring of carbon atoms.
CarbohydrateAn organic compound with the general formula Cx(H2O)y.
CarbonateAn ion consisting of one carbon bonded to three oxygen atoms (CO32-)or a compound containing this ion.
CarbonylFunctional group consisting of a carbon atom double bonded to oxygen, C=O.
Carboxyl groupFunctional group consisting of a carbon double bonded to oxygen and single bonded to a hydroxyl (-COOH).
CarcinogenA cancer-causing agent.
CatalysisA process in which a catalyst increases the speed of a chemical reaction.
CatalystA 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.
CatenationBinding of an element to itself via covalent bonds, forming a chain or ring
CathodeA negative electrode.It is the electrode from which current leaves an electrolytic cell.
Cathode ray tubeA vacuum tube with a source of electrons, a fluorescent screen, and means of accelerating and deflecting the electron beam.
CationA positively charged atom or group of atoms, or a radical which moves to the negative pole (cathode) during electrolysis.
Cationic surfactantAsurfactant in which the hydrophile is positively charged. Examples; quaternary ammonium salts. (see RFF 750.10.01 - SURFACTANTS).
CausticCapable of destroying or eating away by chemical action; a hydroxide of a light metal.
Caustic sodaSodium hydroxide, NaOH.
Celsius temperature scaleTemperature scale where 0°C and 100°C are defined as the freezing and boiling points of water, respectively.
Central atomIn 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 reactionSet of chemical reactions in which products become reactants of another reaction.
ChargeAn electrical charge, a conserved property of subatomic particles determining their electromagnetic interaction.
Charles's lawIdeal gas law that states the volume of an ideal gas is directly proportional to absolute temperature, assuming constant pressure.
ChelateOrganic compound formed by bonding a polydentate ligand to a central metal atom, or the act of forming such a compound.
ChelatedCombined with a metal to form a chelate ring, in which a metal ion is held by coordinate bonds.
ChelationA process in which a metal ion is coordinatively bound to an organic molecule forming a heterocyclic ring.
Chemical analysisThe 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 bondsThe process by which atoms combine to form molecules.
Chemical changeProcess by which one or more substances are altered to form new substances.
Chemical coagulationThe destabilization and initial aggregation of colloidal and finely divided suspended matter by the addition of a floc-forming chemical.
Chemical energyEnergy contained in the internal structure of an atom or molecule.
Chemical equationDescription of a chemical reaction, including the reactants, products, and direction of the reaction.
Chemical equilibriumState of a chemical reaction where the concentration of the reactants and products remains stable over time.
Chemical formulaExpression which states the number and type of atoms in a molecule.
Chemical kineticsThe study of chemical processes and rates of reactions.
Chemical oxygen demandThe 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 propertyCharacteristic which may be observed when matter undergoes a chemical change.
Chemical reactionA chemical change in which reactants form one or more new products.
Chemical symbolOne or two letter representation of a chemical element (e.g., H, Al).
ChemicalAny matter or substance that has mass.
ChemiluminescenceLight emitted as a result of a chemical reaction
Cherenkov radiationCherenkov radiation is the electromagnetic radiation emitted when a charged particle moves through a dielectric medium faster than the velocity of light in the medium.
ChiralRelating to a molecule that cannot be superimposed on its mirror image.
Chiral centerThe atom in a molecule bonded to four different chemical species, allowing optical isomerism.
ChiralityChirality 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.
ChlorinationThe 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 pointThe addition of chlorine to water, sewage, or industrial waste containing free ammonia to the point where free residual chlorine is available.
Chlorination, free residualThe 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 demandThe quantity of chlorine absorbed by wastewater (or water) in a given length of time.
Chlorine, availableThe quantity of chlorine released by a bleaching powder when treated with acid.
Chlorine, combined available residualThat 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 residualFree residual chlorine plus combined residual chlorine.
ChlorofluorocarbonSynthetic compounds containing carbon, chlorine, fluorine, and sometimes hydrogen that are used in refrigerants, propellants, the manufacture of foams, and cleaning solvents.
ChlorophyllThe 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.
ChromatographyAny process for separating materials using two phases, one stationary, and one moving.One example: gas chromatography (gas as moving phase, solid as stationary phase).
CircuitA path through which an electrical current can flow when the path is complete.
ClarificationThe composite wastewater treatment process consisting of flash mixing of coagulants, pH adjusting chemicals, and/or polyelectrolytes, flocculation, and sedimentation.
ClarifierA unit which provides for settling and removal of solids from wastewater.
Closed systemThermodynamic system in which mass is conserved within the system, but energy can freely enter or exit.
Cloud pointAnionics - 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 .
CoagulationThe clumping of particles in order to settle out impurities; often induced by chemicals such as lime or alum.
CoenzymeSubstance that works with an enzyme to aid its function or initiate its action.
CohesionMeasure of how well molecules stick to each other or group together.
Coliform organismsAny of a number of organisms whose presence in wastewater is an indicator of pollution and of potentially dangerous bacterial contamination.
Colligative propertiesProperties 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).
ColloidA substance consisting of particles dispersed throughout another substance.
Combination reactionReaction in which two reactants combine to form a single product.
Combined gas lawLaw which states the ratio of the product of pressure and volume, divided by the absolute temperature, is a constant value.
Combined sewageA sewage containing both sanitary sewage and surface or storm water with or without industrial wastes.
Combining weightThe 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 liquidA liquid which has a flash point above 100F.
CombustionRapid oxidation (burning) accompanied by the release of heat.
Common - ion effectSuppressing effect an electrolyte has on the ionization of another electrolyte that shares a common ion.
Complex ionIon in which a central metal ion is bonded to one or more ions or molecules.
ComplexingThe 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.
CompostingThe 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.
CompoundTwo of more elements combined; a substance having different properties than of the elements used.
ConcentratedHaving a large ratio of solute to solvent.
ConcentrationIn 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.
CondensateWater obtained by evaporation or a product that has changed from a gaseous or vaporous form to a liquid form.
CondensationThe process of vapor molecules forming a liquid.
Condensation reactionChemical reaction in which one of the products is water or ammonia, also known as a dehydration reaction.
Condensed formulaChemical formula in which atom symbols are listed in the order they appear in the molecular structure, with limited bond dashes.
ConductanceA measure of the conducting power of a solution equal to the reciprocal of the resistance. The resistance is expressed in ohms.
ConductivityAbility of a material to carry current or heat.
ConductorMaterial which permits the flow of energy (e.g., electrical conductor, thermal conductor).
ConformerAn isomer that differs from another isomer by rotation around a single bond.
CongenerMember of the same group of elements of the periodic table (e.g., iodine and chlorine).
Conjugate acidA substance which can lose a H+ ion to form a base.
Conjugate baseA substance which can gain a H+ ion to form an acid.
ConjugateMultiple 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 energyLaw which states energy can change forms but may not be created or destroyed.
Conservation of massLaw that states, in a closed system, matter can change forms but not be created or destroyed.
ConstitutionThe types and totals of atoms which makeup a molecule.
Contact coagulationA 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.
ContaminationA general term signifying the introduction into water of microorganisms, chemicals, wastes or sewage which renders the water unfit for its intended use.
Continuous spectrumA spectrum of all the colors of light.
ContractTo become smaller, closer together
Controlled variableVariable that a scientist holds constant in an experiment; the control or constant variable
Conversion factorNumerical ratio that converts a measurement from one unit into another.
Cooling towerA 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 bondCovalent bond between two atoms in which one atom supplies both electrons for the bond.
Coordination compoundCompound containing one or more coordinate bonds.
Coordination numberNumber of atoms bonded to a central atom.
Corrosion inhibitorAn 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.
CorrosionIrreversible damage to a material or tissue due to a chemical reaction.
CorrosiveHaving the power to cause irreversible chemical damage upon contact.
Coulomb's lawLaw 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 bondChemical link between atoms or ions in which the electron pairs are more or less evenly shared between them.
Covalent compoundMolecule that contains covalent chemical bonds.
Covalent radiusValue assigned to an atom such that the sum of the covalent radii of atoms A and B is (approximately) the A-B bond length.
CrenationForming a scalloped shape upon exposure to a hypertonic solution.
Critical micelle concentrationThe solution concentration of a surfactant at which micelles start to form in that solution. (see RFF 705.10.03 - SURFACE TENSION).
Critical pointCritical state; point at which two phases of matter become indistinguishable from one another.
Critical pressureThe lowest pressure required to transform a gas into a liquid at the critical temperature.
Critical temperatureOne 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 massThe amount of a specific radioactive material it takes to create a chain reaction.
Crystal field splittingThe difference in energy between the d orbitals of ligands.
CrystalMatter in which atoms, ions, or molecules are packed into an ordered, repeating three - dimensional pattern.
CrystallizeSolidification of matter into the highly ordered form of a crystal.
CurrentA movement of electrons through a conductor. Measured in amperes.
CyrogenicsStudy of matter at extremely low temperatures
Dalton's LawRelation stating the total pressure of a gaseous mixture equals the sum of the partial pressure of the component gases.
Dative bondCovalent bond between atoms in which one atom provides both electrons for the bond.
Daughter isotopeIn 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 EquationEquation describing the wave properties of matter, stated as wavelength equals Planck's constant divided by the product of mass and velocity.
De Broglie's hypothesisStates that electrons around atoms are in wave formation.
DecantTo remove the liquid portion of a settled mixture without disturbing the sediment.
DecantationMethod of separating mixtures by removing the liquid layer from a precipitate.
DecayChange of an element into a different element, usually with some other particle(s) and energy emitted.
Dechlorination processA 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.
DecompositionWhen a complex molecule becomes broken apart to create two or more smaller ones.
Decomposition reactionChemical reaction in which a single reactant yields two or more products.
DeflagrationType of combustion in which flame propagation is less than 100 m/s and overpressure is less than 0.5 bar.
DegradableThat which can be reduced, broken down or chemically separated.
DegreasingThe process of removing greases and oils from sewage, waste, and sludge.
DehydrationA reaction in which the elements that make up water (twice as many hydrogen as oxygen atoms) are removed from an organic compound.
Dehydration reactionChemical reaction between two compounds in which one of the products is water.
DeliquescenceProcess by which a soluble substance picks up water vapor from the atmosphere to form a solution.
Delocalized electronAny electron in an ion, atom, or molecule that is no longer associated with a particular atom or single covalent bond.
DemineralizationRemoval from water of mineral contaminants. Methods include ion exchange, flash distillation, electrodialysis, or reverse osmosis.
DemulsibiltyA measure of a fluid's ability to separate from water.
DenatureWhen the structure of proteins break down from exposure to heat.
DenseA compact substance or a substance with a high density.
DensityMass per unit volume of a substance.
Dependent variableVariable being measured (tested) in response to changing the independent variable.
DepositionSettling of sediment or particles onto a surface or the phase change from the vapor to solid phase.
DeprotonationChemical reaction in which a compound loses a proton (H+).
Derived unitAn SI unit made from a combination of the base units (e.g., Newton is kg·m/s2).
DesiccantChemical agent that picks up water, often used for drying.
DesublimationPhase change from vapor to solid.
Detention timeThe 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.
DetergentA substance used for removing dirt. Detergents differ from soaps in that detergents are compounds that are derived from sulfur-containing organic acids.
DeuteriumThe isotope of hydrogen that has one neutron.
Dew pointThe 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.
DextrorotatoryAble to rotate plane-polarized light in a clockwise fashion.
DI waterDeionized water, having had all the ions removed.
DialysisThe separation of a colloid from a substance in solution by allowing the solution to diffuse through a semipermeable membrane.
DiamagneticNot attracted to a magnetic field, generally because the material does not contain unpaired electrons.
Diatomaceous earthA 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.
DiffusionThe gradual mixing of the molecules of 2 or more substances by random molecular motion.
DigestionThe biochemical decomposition of organic matter which results in the formation of mineral compounds and simple organic compounds.
DiluentThe thinning agent used to dilute a fluid, usually water.
DiluteTo thin out, or having been thinned out; less than full strength.
Dilute sewageSewage containing less than 150 ppm of suspended solids and BOD (weak sewage).
DilutionWhen a substance, called a solvent, is added to a suspension to reduce the concentration.
DimerA molecule or compound formed by the combination of two identical simple molecules.
DiodeA component that readily passes current in one direction but opposes current flow in the opposite direction.
DipoleProduced 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 momentMeasure of the separation of two opposite electrical charges.
DipoleA separation of electrical or magnetic charges.
Dipole-dipole forcesIntermolecular forces that exist between polar molecules. Active only when the molecules are close together. The strengths of intermolecular attractions increase when polarity increases.
Diprotic acidAcid 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 proportionRelation between two variables such that their ratio is a constant value.
DisaccharideCarbohydrate formed when two monosaccharides bond, removing a molecule of water from their structure.
DisinfectionEffective 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.
DispersionA 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 reactionChemical reaction in which the cation or anion of one reactant is replaced by one from another reactant.
DisproportionationChemical reaction (usually redox) where a molecule forms two or more dissimilar products.
DissociationIn an aqueous solution, the separation of a compound into ions.
Dissociation reactionChemical reaction in which a reactant breaks into two or more parts.
DissolveA 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.
DistillateVapor formed by a distillation, which may be condensed into a liquid for collection.
DistillationThe 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 waterWater 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 cationPositive charged ion with a valence of 2.
DopamineOne 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.
DoseThe measured quantity of a substance, such as a drug, taken at one time.
Double bondChemical bond in which two electron pairs are shared between two atoms.
Double replacement reactionChemical reaction in which two reactants exchange anions/cations to form two new products using the same ions.
DrawdownThe act, process, or result of depleting, as in the drawdown of oil reserves.
Dry iceThe solid form of carbon dioxide
DuctileThe ability of a substance to be drawn out to form a thin wire.
DuctilityProperty of a metal in which it can be stretched without breaking.
DuNouy ring tensiometerA 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.
DyeA substance used to give color to cloth, plastics, paper, or other materials.Dye may be made from plants or by synthetic chemical reactions.
Dynamic equilibriumChemical equilibrium between the forward and reverse reaction in which the rates of reaction are equal to each other.
EDTA titration (EDTA)Ethylenediaminetetraacetic acid (or its salts). A standard method of measuring the hardness of a solution
Effective nuclear chargeNet charge an electron experiences in an atom that has multiple electrons.
EffervescenceFoaming or bubbling when gas is evolved by a liquid or solid.
EfflorescenceProcess by which a hydrate loses water of hydration.
EffluentA liquid that has passed through a processing operation.
Effluent limitationAny 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.
EffusionMovement of gas through a pore or capillary into a vacuum or another gas.
ElasticityPhysical property of matter describing the ability to return to original shape after deformation.
Electrical conductivityMeasure of a substance's ability to carry an electrical current.
Electrical resistivityMeasure of how much a material resists carrying an electrical current.
ElectricityA form of energy coming from charges.
ElectrochemicalDescribes any effect concerned with the electrical properties of solutions and the ions in solutions.
Electrochemical cellDevice that generates a potential difference between electrodes via chemical reactions.
ElectrochemistryScientific study of reactions and species formed at the interface between an electrolyte and a conductor, where electron transfer occurs.
ElectrodeThe anode or cathode of an electrical cell, the device that moves electrons into or out of a solution by conduction.
ElectrolysisChanging the chemical structure of a compound using electrical energy.
ElectrolyteA substance that, when dissolved in water produces a solution that conducts electricity.
Electrolytic cellType of electrochemical cell in which the flow of electric energy from an external source enables a redox reaction.
Electromagnetic radiationLight; self propagating energy that has electric and magnetic field components.
Electromagnetic spectrumComplete range of wavelengths which light can have. These include infrared, ultraviolet, and all other types of electromagnetic radiation, as well as visible light.
Electromotive forceEMF, the electric potential generated by either an electrochemical cell or changing magnetic field.
ElectronA 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 affinityMeasure 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 cloudRegion of negative charge surrounding the atomic nucleus that has a high probability of containing electrons.
Electron configurationDescription of the population of the electronic energy sublevels of an atom.
Electron densityRepresentation of the probability of finding an electron in a specific region around an atom or molecule.
Electron domainThe number of lone electron pairs or bond locations around an atom or molecule.
Electron geometryStructure of a compound based on the arrangement of its electrons.
Electron pair repulsionPrinciple that electron pairs surrounding a central atom orient themselves as far apart as possible; used to predict geometry.
Electron spinProperty of an electron related to its spin about an axis, described by a quantum number as either +1/2 or -1/2.
ElectronegativityProperty of an atom that reflects its ability to attract electrons in a chemical bond.
ElectrophileAtom or molecule that accepts an electron pair to form a covalent bond.
ElectrophoresisA 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.
ElectroplatingProcess of adding a metal coat to a material by using a reduction reaction.
ElectrostaticHaving 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 forcesForces between particles due to their electrostatic charges.
ElectrumA natural alloy of gold and silver.
ElementA substance that cannot be resolved into two or more other substances; a substance made up of atoms with the same atomic number.
Element symbolThe one or two letter abbreviation of a chemical element (e.g., H, Cl).
Elementary reactionChemical reaction in which reactants form products in a single step without a transition state.
Emission spectrumRange of wavelengths emitted by an atom stimulated by electricity or heat.
EmissionProduct of a combustion reaction, aside from heat and light (e.g., carbon dioxide).
EmollientA substance that softens or smoothes.
Empirical formulaThe simplest whole number ratio of elements in a compound, ie CH2.
EmulsifierA substance that promotes the dispersion of small globules of one liquid in another liquid when the two liquids will not mix.
Emulsion polymerizationA heterogeneous, free-radical polymerization process in which the bulk of the polymeric product in formed inside micelles.
EmulsionA 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.
EnantiomerOne of a pair of non-superimposable, mirror-image stereoisomers.
End pointThat 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.
EndothermicProcess that absorbs heat from its surroundings as the reaction proceeds.
Endothermic reactionTakes more energy to start it than it gives back. A reaction that needs energy to keep it going.
EnediolAn alkene enol with a hydroxyl group attached to both carbon atoms of the C=C bond.
EnergyThe ability to do work and transfer heat.
Energy levelThe current level of energy an electron has within an atom.
EnrichmentThe 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 changeThe energy change of a system at constant pressure.
Enthalpy of atomizationQuantity of enthalpy change when chemical bonds are broken in a compound to form individual atoms.
Enthalpy of reactionDifference between total enthalpy of products and total enthalpy of reactants of a chemical reaction.
EnthalpyThermodynamic property of a system that is the sum of the internal energy and the product of pressure and volume.
EntropyMeasure of the disorder of a system.
EnzymaticRelating to the activity of enzymes, which are biological catalysts that play crucial roles in most biological processes, including metabolism and gene expression.
EnzymeA 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 additiveA lubricant additive or system which prevents sliding metal surfaces from seizing under conditions of extreme pressure and force.
EpimerOne of two steroisomers with more than one chiral center that differ in stereochemical configuration at only one.
EquilibriumWhen 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 constantValue 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 expressionsThe 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 pointPoint in a titration where the titrant completely neutralizes the analyte.
Essential amino acidAmino acid needed in the diet because an organism cannot synthesize it.
EsterRCO2R′, where R is the hydrocarbon parts of the carboxylic acid and R′ is the alcohol.
EtherOrganic compound containing two aryl or alkyl groups bound to an oxygen, R-O-R'.
EutecticHomogeneous solid mixture of at least two types of atoms or molecules that form a superlattice (usually a mix of alloys).
EvaporationChanging of a liquid to a vapor at any temperature below its boiling point.
Excess reactantReactant left over in a reaction because it is present in a great amount than needed to react with the limiting reactant.
Excited stateAtom, ion, molecule, or subatomic particle in a higher energy level than its ground state.
ExcretionThe process of ridding the body of metabolic waste products.
Exergonic processA process that liberates energy.
ExergonicReleasing energy to its surroundings.
ExothermicProcess that gives off heat to the environment.
Exothermic processA thermodynamic process in which heat flows from a system to the surroundings.
Exothermic reactionA chemical reaction that releases heat.
ExothermicReleasing energy to the environment in the form of heat; a type of exergonic process
ExponentiationRaising something to a power.
Extensive propertyProperty of matter that depends on the quantity of matter that is present (e.g., volume).
F orbitalElectron orbital with l = 3 for the angular momentum quantum number,
FacultativeHaving 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 constantA physical constant equal to the electric charge of one mole of electrons, 96485.33 C/mol.
FatA solid ester of a long-chain carboxylic acid with glycerol.
Fatty acidA carboxylic acid with a long hydrocarbon side chain.
FeedstockAny unprocessed material used as a supply for a manufacturing process.
FenfluramineAmphetamine-like component of fen-phen that suppresses appetite by increasing seratonin levels in the brain.
FilterTo 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 backwashThe 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.
FiltrationThe process of separating solids from a liquid by means of a porous substance through which only the liquid can pass.
Fire pointThe lowest temperature a vapor will initiate and sustain combustion.
First law of thermodynamicsLaw which states the total energy of a system and its surroundings is a constant value; the law of conservation of energy.
FissionThe splitting of an atomic nucleus, which results in two or more lighter nuclei and a release of energy.
Flame testAn analytical technique used to identify ions based on their emission spectrum in a flame.
FlammableEasily ignited or capable of sustained combustion.
Flash pointThe 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.
FloatationThe 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.
FlocA very fine, fluffy mass formed by the aggregation of fine suspended particles.
FlocculationThe process of separating suspended solids from wastewater by chemical creation of a coagulated, or flocculent masses.
FlowrateUsually 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.
FluidA 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.
FluorescenceLuminescence released when an atom absorbs electromagnetic radiation and emits a photon when the electron falls to a lower energy state.
FluxA material used to promote joining of metals in soldering.
Foam boosterA substance which enhances the quality and/or longevity of a foam.
FoamA substance containing gas bubbles trapped within a liquid or solid.
ForceAn 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 chargeThe 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 reactionReaction in which one mole of a product is formed.
FormazinA 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).
FormulaA shorthand way of showing the composition of a substance with the use of symbols and numerical subscripts.
Formula mass / weightThe sum of the atomic weights of the atoms in a compound's empirical formula.
FormulationA blend of a number of base chemicals and additives designed to accomplish a specific purpose.
Fractional distillationProcess which separates components of a mixture according to their boiling points.
Free electronElectron which is not attached to a nucleus.
Free energyThe amount of internal energy of a system that is available to do work.
Free radicalAn atom or molecule with an unpaired electron.
Freezing point depressionLowering the freezing point of a liquid by adding another compound to it.
Freezing pointTemperature at which a liquid transitions to a solid (not always the same as melting point).
FreezingProcess in which a liquid changes to a solid.
FrequencyThe number of complete waves passing a point in space in a given amount of time.
FuelA material that can be burned to provide a source of energy.
FumigantA gaseous substance used to disinfect an object or to destroy pests.
Functional groups / moietyGroup of atoms in a molecule that are responsible for characteristic reactions and properties.
FungicidesA chemical that kills fungi or prevents them from growing.
FuseA 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.
FusionCombining light atomic nuclei to form a heavier nucleus, accompanied by the release of energy.
Galvanic cellElectrochemical cell where reactions between dissimilar conductors occur through a salt bridge and electrolyte.
GalvanizeThe process of covering iron with a coat of zinc to make it less reactive to air and water.
GalvanometerA device that is very sensitive and able to detect even small flows of electrons through a wire.
Gamma radiationHigh energy ionizing photons, originating from the atomic nucleus.
Gamma rayElectromagnetic radiations beyond the X-rays in frequency. They are usually produced in nuclear reactions.
GardnerA unit of color density. Measured by comparison of the material to be analyzed against standards of known intensity.
gas chromatographyAn 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.
GasA 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.
GasoholA mixture of 90% gasoline and 10% ethyl alcohol that is used as an automotive fuel.
GasolineA volatile, flammable, liquid mixture of hydrocarbons, obtained from petroleum, and used as fuel for internal-combustion engines.
Gay-Lussac's lawForm 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 counterInstrument that measures radiation output.
GelA 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.
GeneThe 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 isomerMolecules 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 energyThe energy of a system that is available to do work at constant temperature and pressure.
GlassAn amorphous solid.
GlucoseA 6-carbon sugar that plays a major role in cell metabolism.
GlycogenA 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.
GlycolipidA lipid covalently linked to a sugar or polysaccharide. These biomolecules are important parts of animal cell membranes.
GlycolysisA 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 bondA covalent bond between a carbohydrate and a functional group or another molecule.
Grab sampleA single sample of wastewater taken at neither set time nor flow.
Graham's LawRelation stating the rate of effusion of a gas is inversely proportional to the square root of its molecular mass or density.
Grain alcoholPurified form of ethyl alcohol made from distilling fermented grain.
Gram molecular massThe mass in grams of one mole of a molecular substance.
GraphiteThe 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 analysisA set of quantitative analytical techniques based on measurement of a sample's mass.
Green chemistryBranch of chemistry concerned with lessening the environmental effect of chemicals, including development of new materials and processes.
Ground stateThe lowest energy state of an atom, ion, molecule, or subatomic particle.
Ground wireA conductor leading from electrical equipment to a low resistance connection with the earth.
GroupA family of elements with similar chemical properties, represented by a vertical column in the periodic table.
Haber processMethod of making ammonia or fixing nitrogen by reacting nitrogen and hydrogen gas
Half-cellAn 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-reactionA reaction that shows the electrons involved in an oxidation or reduction step of a reaction.
HalideA negatively charged ion of the group VIIA elements.
Halide ionA singlet halogen atom, which has a charge of -1 (e.g., Cl)
HalogenThe group VIIA elements in the periodic table.
HalogenAn element in Group VII A of the periodic table (e.g., Br, Cl).
Halogenated hydrocarbonA hydrocarbon that contains one or more halogen atoms.
Hard waterWater that contains high amounts of calcium and/or magnesium cations.
Hardness1) 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.
HeatThe transfer of (thermal) energy between two objects that are at different temperatures.
Heat capacityQuantity 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 metalA 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 principlePrinciple that states it is impossible to determine both the position and momentum of a particle at once with perfect accuracy.
Henderson - Hasselbalch equationAn approximation that relates the pH or pOH of a solution, the pKa or pKb, and the ratio of concentration of dissociated species.
Henry's LawLaw 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 LawLaw that states the energy change in an overall reaction equals the sum of the energy changes in its individual (partial) reactions.
heterocycleA compound containing at least one ring that consists of both carbon and non-carbon atoms .
HeterogeneousDescribes a material or substance or chemical reaction which is not the same throughout in its properties, composition, or state of matter.
Heterogeneous mixtureA mixture that lacks a uniform composition such that at least two components are present with identifiable properties.
Heterogeneous reactionChemical reaction in which reactants are different phases from each other.
HomeopathyA system of disease treatment involving application of minute doses of a remedy that, in a healthy person, would produce symptoms of the disease.
HomogeneousDescribes a material or substance or chemical reaction which is the same throughout in its properties, composition, or state of matter.
HomopolymerPolymer in which every mer unit is identical.
Hybrid orbitalOrbital formed by the combination of two or more atomic orbitals.
HybridizationA mixing process, often applied to description of atomic orbitals, producing orbitals that have characteristics intermediate between the various types of orbitals involved.
HydrateA crystalline solid with molecules of water trapped in the solid state structure, which can often be removed partly or completely by relatively gentle heating.
HydrationHaving solvent molecules of water surrounding and becoming attached to ions or molecules of the solute.
Hydration reactionReaction in which a hydrogen and hydroxyl ion are attached to a carbon in a C-C double bond.
HydrocarbonA chemical compound containing only hydrogen and carbon; the largest source of hydrocarbons comes from petroleum crude oil.
Hydrogen bondA 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 concentrationThe 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.
HydrogenationThe 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.
HydrolysisCleavage of a covalent bond brought about by water; the H- and -OH of water typically become attached to the respective cleavage fragments.For example:
HydrolyzeTo add hydrogen or hydroxyl to a substance.
HydrometerInstrument used to measure the relative densities of two liquids.
Hydronium ionThe H3O+cation.
HydrophileA material having an affinity for, attracting, adsorbing or absorbing water. The opposite of hydrophobe.
Hydrophile-Lipophile balanceA measure of the relative simultaneous attraction of an surfactant to both phases of an emulsion.
HydrophobeA material lacking affinity for, repelling, failing to adsorb or absorb water. The opposite of hydrophile.
HydrophobicProperty of repelling water.
HydrotropeA 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 groupFunctional group consisting of a hydrogen atom covalently bonded to an oxygen atom (-OH).
Hydroxyl numberA measure of the hydroxyl content of ethoxylates. Measured titrimetrically. Usually used for molecular weight determinations.
Hydroxyl radicalAn oxygen and hydrogen atom occurring as a group (OH-).
HygroscopicAble to absorb or adsorb water from the surroundings.
HypertonicHaving higher osmotic pressure than another solution.
HypothesisA scientific "hunch," a tentative explanation of or prediction derived from experimentation.
Ideal gas constantPhysical constant in the Ideal Gas Law, equal to the Boltzmann constant but with different units.
Ideal gas lawPV=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 gasGas in which molecules have negligible size and kinetic energy dependent only on temperature.
ImmiscibleProperty of two substances being unable to combine to form a homogeneous mixture; unable to mix
ImpedanceTotal opposition to flow of current, measured in ohms; combined effort of resistance, inductance, and capacitance.
IncinerationBurning 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 variableThe variable that is controlled or changed in an experiment to test its effect on the dependent variable.
IndicatorA compound that changes color at a particular pH, or over a particular narrow range of pH, used to show titration end points.
Inductive effectEffect a chemical bond has on the orientation of adjacent bonds in a molecule.
Industrial sewageSewage in which industrial wastes predominate.
InfluentSewage, water or other liquid, either raw or partly treated, flowing into a reservoir basin, or treatment plant or any part thereof.
InhibitorSubstance that slows or prevents a chemical reaction.
Inorganic chemistryStudy of chemistry of molecules of non-biological origin (not containing C-H bonds).
InsolubleUnable to dissolve in a solvent.
Intensive propertyProperty of matter that is independent of the quantity of matter in a sample.
IntercalationThe binding of a molecule between adjacent base pairs in DNA.
IntermediateMolecules that exist only during a chemical reaction; not before or after the reaction.
IntermolecularBetween molecules.Intermolecular forces are those forces between molecules.
Intermolecular forceThe sum of all forces between neighboring molecules.
Internal energyThe total energy (U) of a closed system.
IntramolecularRefers to a characteristic within one molecule or ion, referring only to the atoms in the molecular or ion.
Intramolecular forceForce within molecules. Forces caused by the attraction and repulsion of charged particles.
Intrinsic propertyProperty of matter that is independent of the quantity of matter present.
Inverse proportion / relationshipRelationship between variable such that their product is a constant value.
IonAn 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 exchangeA 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 forceIntermolecular force that exists between charged particles and partially charged molecules.
Ion-exchangerA 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 bondChemical link between atoms caused by electrostatic force between opposite charged ions.
Ionic compoundCompound formed by ions bonding together due to electrostatic forces (differing electronegativity values).
Ionic equationChemical equation in which electrolytes in aqueous solution are written as dissociated ions.
Ionic radiusHalf the distance between two ions just touching each other.
IonicPertaining to carrying a net electrical charge at the atomic or molecular level.
IonizationA 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 energyThe energy needed to remove an electron from a gaseous atom.
IonizeWhen a substance breaks into its ionic components.
Irreversible reactionA chemical reaction after which the resulting agents cannot be changed back into the reactions ingredients.
IsoelectronicChemical species that have the same electronic structure and thus same number of valence electrons.
Isolated systemThermodynamic system that can't exchange energy or matter outside of the system.
IsomerChemical compound that has the same number, and kinds of atoms as another compound, but a different structural arrangement of the atoms.
Isomerization processProtocol in which straight chain hydrocarbons are converted into branched chain hydrocarbons.
IsotopeAtoms that have the same number of protons, but different numbers of neutrons and thus different atomic weight values.
IUPACInternational Union of Pure and Applied Chemistry, an authority on chemical standards.
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.
jouleSI unit of energy equal to the kinetic energy of a 1 kg mass moving at 1 m/s.
JTUSee jackson turbidity unit.
KelvinThe SI Unit of temperature. It is the temperature in degrees Celsius plus 273.15.
KeratinA fibrous protein produced by chordates. It may be found in hair, skin, claws, and wool.
KetoneCompound containing a carbonyl functional group (C=O) between two groups of atoms
KetoseA simple sugar that has the reactions of a ketone.
KiloPrefix meaning "one thousand".
KilogramBase 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 energyThe 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 theoryA theory of the behavior of matter.
KlettA unit of color density. Measured by the light absorption of a clear solution using a Klett-Summerson photoelectric colorimeter.
Krafft pointThe temperature at which the solubility of an ionic surfactant becomes equal to the critical micelle concentration.
Labile complexA complex ion that quickly reaches equilibrium with ligands in the surrounding solution.
LagoonIn wastewater treatment, a shallow pond where sunlight, bacterial action, and oxygen interact to restore wastewater to a reasonable state of purity.
LanthanidesSubset of transition metals characterized by filling of the 4f sublevel, usually atomic number 58 - 71
LaserAcronym 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.
LatticeA regular arrangement of points in space in 3 dimensions.
Lattice energyEnthalpy change of the process by which opposite - charged ions in a gas combine to form a solid ionic lattice.
Law of chemical equilibriumAn expression of the relationship between the concentration of reactants and products of a chemical reaction mixture at equilibrium.
Law of combining volumeRelation 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 energyLaw that states energy can neither be created nor destroyed, although it may change from one form into another.
Law of conservation of mass / matterLaw that states matter in a closed system may be neither created nor destroyed, although it may change forms.
Law of constant compositionChemistry law that states samples of a pure compound contain the same elements in the same proportions by mass.
Law of definite proportionLaw that states all samples of a compound contain the same proportion of elements by mass.
Law of multiple proportionLaw that states element combine in ratios of small whole numbers to form molecules.
LawA general rule that explains a body of scientific observations. Laws are stated in words, but expressed by mathematical equations.
Le Chatlier's principleStates that a system at equilibrium will oppose any change in the equilibrium conditions.
LeachateThe 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.
LevorotatoryAble to rotate plane-polarized light in a counterclockwise fashion.
Lewis acid base reactionChemical reaction that forms at least one covalent bond between an electron pair donor (Lewis base) and electron pair acceptor (Lewis acid).
Lewis acidChemical species that can act as an electron pair acceptor.
Lewis baseA substance that is an electron pair donor.
Lewis structureRepresentation of a molecule that uses dots to show electrons around atoms and lines to show covalent bonds.
LigandA chemical species that donates or shares at least one electron via a covalent bond with a central ion or atom.
LightHas both wave and particle properties.
LimeAny 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.
LimewaterCommon name for a solution of calcium hydroxide.
Limiting reagentA 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.
LimnologyThe study of the physical, chemical, meteorological and biological aspects of fresh water.
Line spectraSpectra generated by excited substances. Consists of radiation with only specific wavelengths.
LipidA fatty, waxy or oily non-polar organic compound that is characteristically insoluble in water but readily soluble in organic solvents.
LiquefactionProcess of converting a material from a solid or gas phase into the liquid phase.
LiquidA state of matter that has a definite size or volume but not a definite shape.
LiterUnit 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.
LitmusPlant pigment commonly used as an acid base indicator.Litmus is red (or pink) in an acid, and blue in a base.
Litmus paperFilter paper used as a pH paper that has been treated with a water - soluble dye obtained from lichens.
London dispersion forceWeak intermolecular force between atoms or molecules in close proximity to each other, due to electron repulsion.
Lone pair/unshared pairTwo electrons that are not shared between atoms within a molecule.
LyeCommon name for solution of sodium hydroxide.
LyophileA material having an affinity for, attracting, adsorbing or absorbing oil. The opposite of lyophobe.
MacromoleculeName 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 ruleRule that describes filling of electron orbitals in atoms due to shielding of nuclear charge by inner electrons.
Main group elementAny of the elements in the s and p blocks of the periodic table.
MalleabilityThe property of a metal that allows it to be hammered, rolled, pressed or forged.
MalleableAble to be shaped or pounded with a hammer, usually applied to metals.
ManometerAn 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.
MassThe quantity of matter in a body as measured by its resistance to a change in acceleration; different but proportional to weight.
Mass defectDifference between the mass of an atom and the sum of the masses of its protons, neutrons, and electrons.
Mass numberThe 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 percentageConcentration calculated as mass of a component divided by total mass of mixture or solution; w/w%.
Mass spectroscopyAnalytical technique used to separate and/or identify components of a mixture based on mass and electrical charge.
MatterAnything that has mass and occupies volume.
MeasurementQuantitative or numerical data describing an object or event.
Medicinal chemistryBranch of chemistry concerned with design, synthesis, and study of pharmaceuticals.
Melting and boiling temperaturesCaused by the van der waals interaction. Solids melt and liquids evaporate when the van der waals forces between molecules are broken.
Melting pointTemperature at which the solid and liquid phase of matter coexist in equilibrium.
MeltingPhase change of matter from solid to liquid.
MeniscusThe 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.
MercaptanOrganic sulfur compound containing an alkyl or aryl group and a thiol group.
Mercapto groupFunctional group consisting of a sulfur bonded to a hydrogen; -SH.
MetabolismSet of biochemical reactions that store chemical energy and convert it into a form an organism can use.
MetaboliteA chemical product of metabolism.
MetalSubstance that has high conductivity and other metallic properties, including tendency to form cations, often identified by group on the periodic table.
Metallic characterSet of chemical properties associated with metals, including the ability to lose outer valence electrons to form cations.
Metallic compoundChemical compound that contains one or more metal atoms.
MetalloidElement with properties intermediate between those of metals and nonmetals (e.g., silicon).
MeteoriteA mass of stone or metal that has reached the earth from outer space.
MeterEither (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.
MethylFunctional group containing a carbon bonded to three hydrogen atoms, -CH3.
MethylatedHaving a methyl group (CH3).
MicelleColloidal aggregates of surfactant molecules. Micelles first form in a surfactant solution at a well-defined concentration known as the Critical Micelle Concentration.
MicroA prefix meaning one-millionth of a unit.
MicroliterUnit of volume that is one - millionth of a liter one cubic millimeter.
MicromolarApproximately 1x10-6 moles/liter.
MicronUnit of length equal to one-millionth of a meter; a micrometer.
MicroorganismOrganisms (microbes) observable only through a microscope; larger, visible types are called macroorganisms.
MicroscopicSeeing 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 experimentMeasured the actual charge on an electron.
Mineral acidAny inorganic acid (e.g., sulfuric acid).
MiscibleSoluble or able to be mixed to form a solution, typically applied to fluids.
MitochondrionA membrane-bound organelle that carries out oxidative phosphorylation and produces most of the ATP in eucaryotic cells.
MixtureComposed of two or more substances, but each keeps its original properties.
ModeratorMaterial that slows or moderates the speed of neutrons.
Mohs scaleA 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.
MoietyGroup of atoms in a molecule that are responsible for its characteristic chemical behavior.
MolalA solution concentration having a mole of solute per 1,000 grams of solvent, usually water.
MolalityA measure of solution concentration expressed in moles of solute per 1,000 grams of solvent.
MolarAn term expressing molarity, the number of moles of solute per liters of solution.
Molar enthalpy of fusionEnergy needed to change one mole of a substance from solid to liquid phase at constant pressure and temperature.
Molar enthalpy of vaporizationEnergy needed to change one mole of liquid to the gas phase at constant pressure and temperature.
Molar heat capacityHeat energy required to raise the temperature of 1 mole of a substance 1 Kelvin.
Molar massMass of one mole of a substance.
Molar volumeVolume of one mole of a substance.
MolarityThe number of moles of solute (the material dissolved) per liter of solution. Used to express the concentration of a solution.
MoleThe amount of substance that contains the same number of elementary particles as are found in exactly 12 g of carbon-12.
Mole fractionThe number of moles of a particular substance expressed as a fraction of the total number of moles.
Mole ratioRatio or fraction comparing the numbers of moles of any two components involved in a chemical reaction.
Molecular equationBalanced chemical equation in which ionic compounds are expressed as molecules rather than ions.
Molecular formulaShows the number of atoms of each element present in a molecule.
Molecular geometryShape of a molecule, based on the relative positions of the atoms.
Molecular massThe combined mass (as given on the periodic table) of all the elements in a compound.
Molecular orbitalWave function of an electron in a molecule.
Molecular weightThe sum of the atomic weights of all the atoms in a molecule.
MoleculeThe simplest structural unit of a substance that retains the properties of the substance, and is composed of one or more atoms.
Monatomic ionAn ion formed by a single atom.
MonomerA 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.
MonooxygenaseAn 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 acidAcid that donates a single proton or hydrogen atom per molecule in aqueous solution.
MonosaccharideA 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 liquorSolution remaining after crystals are removed from a crystallization solution.
MSDSAcronym for Material Safety Data Sheet, a written document outlining safety information about a chemical.
Multiple bondA bond formed when two or more pairs of electrons are shared between two atoms.
Muriatic acidcommon name for hydrochloric acid, HCl.
Nano-Prefix meaning one billionth or 10-9.
NaphthenesCyclic aliphatic hydrocarbons from petroleum with the general formula CnH2n.
Natural abundanceAverage percentage of a given isotope naturally occurring on Earth.
NephelometerAn instrument that measures scattered light in a liquid.
Nephelometric turbidity unit (NTU)A standard unit of turbidity measurement, equivalent to FNU.
Net ionic equationChemical equation that lists only the species participating in the reaction.
Network solidMaterial consisting of an array of repeating covalently bonded atoms.
NeurotransmitterA substance that transmits nerve impulses across a synapse.
NeutralAn object that does not have a positive or negative charge.
neutral solutionAqueous solution with a pH of 7.
NeutralizationChemical addition of either acid or base to a solution such that the pH is adjusted to 7.
Neutralization reactionA reaction between an acid and a base that results in salt and water.
NeutronA 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.
NitrificationThe conversion of nitrogenous matter or free nitrogen into nitrates and ammonia by bacteria.
NitrogenaseAn enzyme system that catalyzes the reaction of molecular nitrogen (N2) to ammonia (NH3).
NitrosaminesA group of organic compounds with the basic structure NNO, some of which are powerful cancer-causing chemicals.
NMAn abbreviation for nanometers. A nanometer is equal to 10-9 meters.
Noble gas coreShorthand notation used writing atomic electron configuration in which previous noble gas configuration is replaced by the element symbol in brackets.
Noble gasElement from Group 8 of the periodic table (e.g., xenon, argon).
Noble gasesA family of elements that makes up column 18 of the periodic table. They are very stable due to their full outer electron shells.
NodePart of the orbital area in an atom where it is impossible to find an electron.
NomenclatureThe systematic naming of chemical compounds.
Nonbonding electronElectron in an atom that does not participate in a chemical bond with other atoms.
Non-electrolyteA substance that dissolves in water to form a solution that is non-conducting.
Non-ionic surfactantsA 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.
NonmetalElement that does not display metallic properties, typically referring to elements located in the upper right corner of the periodic table.
Nonoxidizing acidAn acid that cannot act as an oxidizing agent.
NonpolarHaving no poles.Used to refer to a bond or molecule that overall has no separation of electrical charge.
Nonpolar bondChemical bond with even distribution of charge such that it does not have positive or negative poles.
Nonpolar moleculeMolecule that has even distribution of charge such that it does not have positive and negative sides.
Nonpolar covalent bondA bond where elections are equally shared between two atoms.
Nonsettleable matterThe suspended matter which neither settles nor floats to the surface of water in a period of one hour.
Nonsettleable solidsWastewater 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 reactionChemical reaction that cannot occur without input of external work.
NonvolatileSubstance that does not readily evaporate into a gas under ordinary conditions.
NorepinephrineA neurotransmitter that increases heart rate, blood pressure, and is related to increased motor activity. It is the precursor to epinephrine.
NormalA solution concentration of one gram equivalent per liter of solution.
Normal boiling pointTemperature at which a liquid boils at 1 atm of pressure (sea level).
Normal concentrationEither 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 pointTemperature at which a solid melts at 1 atm of pressure.
NormalityA measure of solution concentration expressed in equivalent weights of solute per liter of solution.
NTUSee nephelometric turbidity unit.
Nuclear fissionSplitting of atomic nuclei into two or more lighter nuclei, accompanied by an energy release.
Nuclear radiationParticles and photons emitted during reactions in the atomic nucleus.
Nuclear fusionwhen parts of the nucleus of atoms are forced together to create a new one.
Nuclear reactionWhen a reaction affects the nucleus of an atom.
NucleationProcess of vapor droplets condensing into a liquid, bubbles forming in a boiling liquid, or particle accretion to grow crystals.
NucleonThe particles in the nucleus of an atom.
NucleophileAtom or molecule that donates an electron pair to form a covalent bond.
NucleosideA biologically important molecule consisting of an amine-containing purine or pyrimidine base joined to ribose, a 5-carbon sugar.
NucleusThe central part of an atom that contains the protons and neutrons. Plural nuclei.
NuclideAn atom or ion characterized by the proton and neutron composition of its nucleus.
Null hypothesisProposition that there is no effect of a treatment or no relationship between an independent and dependent variable.
NutraceuticalA food or part of food that confers health or medical benefits.
NutrientMaterials which are considered essential to the support of biological life.
Octane numberValue that indicates resistance of motor fuel to engine knock relative to the knock from isooctane (100) and heptane (0).
OctetIn 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 rulePrincipal that atoms in an atomic bond share their 8 outer electrons.
OHMA 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.
OlefinA hydrocarbon containing a carbon-carbon double bond. Olefins are also known as alkenes.
OligomerA 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 flowTo 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.
OpacifierA substance, such as fatty acid esters, which, when added to a clear formulation, renders that formulation opaque - similar to pearlizer.
Open systemA system able to freely exchange matter and energy with its surroundings.
OrbitalA region of space where there is a high probability of finding an electron in an atom or ion.
Organic chemistryStudy of the chemistry of compounds containing carbon chemical bonded to hydrogen.
Organic matterChemical compounds based on carbon chains or rings, and also containing hydrogen with or without oxygen, nitrogen, or other compounds.
Organic nitrogenNitrogen combined in organic molecules such as protein, amines, and amino acids.
OrthophosphateAn acid or salt containing phosphorus as PO4, such as K3PO4 (potassium phosphate).
OsmosisMovement 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.
OxidantA reactant that oxidizes or removes electrons from another reactant in a redox reaction.
OxidationIn 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 / valenceThe electrical charge of a central atom in a coordination compound if all electron pairs and ligands were removed.
Oxidation processAny 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 reactionA reaction where a substance loses electrons.
Oxidation stateThe 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-reactionA reaction involving the transfer of electrons.
OxideAn ion of oxygen with an oxidation state equal to 2 (e.g., iron oxide).
OxidizerA reactant that removes electrons from another reactant in a redox reaction.
Oxidizing agentAn oxidizer; a reactant that removes electrons from another reactant.
OxoacidWhen one or more hydroxide (OH) groups are bonded to a central atom.
OxyanionAn anion that contains the element oxygen.
OxygenateLiquid 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.
OzoneOxygen 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 layerAn 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.
ParamagnetismProperty of material characterized by being attracted to a magnetic field.
Parent atomAtom that undergoes radioactive decay, resulting in one or more daughter atoms.
Parent isotopeAn element that undergoes nuclear decay.
Parent nuclideNuclide that decays into a specific daughter nuclide during radioactive decay.
Partial pressureThe pressure a gas in a mixture of gases would exert if it occupied the volume by itself, at the same temperature.
ParticleSmall portion of matter.
ParticulateSmall 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 bacteriaBacteria which may cause disease in the organisms by their parasitic growth.
Pauli exclusion principlePrinciple that says no two electrons or other fermions can have identical quantum numbers in the same atom or molecule.
PearlizerA substance, such as glycol distearate (EGDS), which, when added to a formulation, imparts an opalescent finish to that formulation.
PeptideA small polymer of amino acids, formed by the condensation copolymerization of several amino acids.
Percent compositionExpresses the mass ratio between different elements in a compound.
Percent yieldThe percentage of yield that occurred versus the theoretical yield.
Percentage compositionCan 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.
PeriodA series of elements, arranged in order of atomic number represented by a horizontal row on the Periodic Table.
Periodic lawLaw that states the properties of elements recur in a predictable and systematic way when they are arranged by increasing atomic number.
Periodic tableA 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 trendRegular variation in the properties of elements with increasing atomic number.
PeriodicityRecurring variations in element properties with increasing atomic number due to trends in atomic structure.
PeriplanarDescribes two atoms or groups of atoms in the same plane as each other with respect to a single bond.
PeroxideA polyatomic anion with molecular formula O22-.
PetroleumCrude oil; natural flammable hydrocarbon mixture found in geologic formations.
pHA 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 adjustmentA means of maintaining the optimum pH through the use of chemical additives.
pH indicatorCompound that changes color over a range of pH values.
pH meterInstrument that measure pH of a solution based on the voltage between two electrodes in the solution.
PharmacologyThe science of drugs; the properties of drugs related to their therapeutic effects.
Phase changeChange in the state of matter of a sample (e.g., liquid to vapor).
Phase diagramChart showing the phase of a substance according to temperature and pressure.
PhaseDistinct form of matter with uniform chemical and physical properties.
Phenolphthalein alkalinitya 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).
PhenolphthaleinAn organic pH indicator, C20H14O4.
PhentermineAmphetamine-like component of fen-phen that increases metabolism by raising the body's levels of dopamine and norepinephrine.
PhlogistonPhlogiston 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.
PhosphorescenceLuminescence 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 effectThe emission of electrons from metal when the metal is struck by light.
PhotonMassless packet of energy, which behaves like both a wave and a particle.
PhotosynthesisProcess 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 changeChange that alters the form of matter but not its chemical composition.
Physical propertyProperties of a substance that can be observed without using a chemical reaction that would change the substance.
PhytoplanktonAlgae, 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.
PhytoremediationUsing plants to clear toxic metals from the environment by chelation.
Pi bondcovalent bond formed between two neighbor atom unbonded pi orbitals.
pKaNegative base 10 log of the acid dissociation constant; lower pKa correlates to stronger acid
pKbNegative base 10 log of the base dissociation constant; lower pKa correlates with stronger base.
PlanckPlanck 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 constantproportionality constant that relates photon energy to frequency; 6.626 x 10-34 J·sec.
PlasmaState of matter with no defined shape or volume consisting of ions and electrons.
PnictogenMember of the nitrogen element group.
pOHMeasures the basicity of a solution. It is the negative log of the concentration of the hydroxide ions.
Polar bondType of covalent bond in which the electrons are unequally shared between the atoms.
Polar moleculeMolecule containing polar bonds such that the sum of the bond dipole moments is not zero.
PolarizabilityIndication 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.
PollutantA substance that contaminates an environment.
Polyatomic ionIon comprised of two or more atoms.
PolycarbonateA polymer in which the repeating unit is an organic carbonate [-R-O-C(O)-O-]n.
PolymerMolecules 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 hydrocarbonHydrocarbon made of fused aromatic rings.
Polyprotic acidAcid able to donate more than one hydrogen atom or proton per molecule in an aqueous solution.
PorosityThe ratio of the size of a material's pores to the volume of the material's mass.
PositronThe antimatter counterpart to an electron, which has a charge of +1.
Potable waterWater suitable for drinking or cooking purposes from both health and aesthetic considerations.
Potential differenceWork required to move an electric charge from one point to another.
Potential energyThe energy an object has because of its composition or position.
PPBParts per billion
PPMParts per million
PrechlorinationChlorination of water prior to filtration, or chlorination of sewage prior to treatment.
PrecipitantA chemical or chemicals that cause a precipitate to form when added to a solution.
PrecipitateTo form an insoluble compound by reacting salts or altering a compound's solubility.
Precipitation reactionChemical reaction between two soluble salts in which one product is an insoluble salt.
PrecisionThe agreement of repeated measurements with each other.
PrecursorIn metabolism, a chemical substance from which another chemical substance is formed
PreservativeA chemical added to a product to inhibit the growth of bacteria.
PressureMeasure of force per unit area.
PretreatmentAny 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 standardVery pure reagent.
Principal energy levelPrimary energy signature of an electron, indicated by quantum number n.
Principal quantum numberThe number related to the amount of energy an electron has and therefore describing which shell the electron is in.
ProductSubstance formed as a result of a chemical reaction.
ProofVolume percentage of ethyl alcohol in an alcoholic beverage.
PropertyA characteristic of matter such as color, density, brittleness, etc..
ProportionAn equality between two ratios.
Protecting groupA ground used in preventing undesired reactions.
ProteinA biological polymer formed by condensation reactions among a set of 20 different amino acids.
ProtonParticle found in a nucleus with a positive charge. Number of these gives atomic number.
ProtonatedHaving acquired an additional proton (H+).
ProtonationAddition of a proton to an atom, ion, or molecule.
PSIUnit of pressure; pounds per square inch.
Pure substanceSample of matter with constant composition and distinct chemical properties.
PutrefactionBiological decomposition of organic matter accompanied by the production of a foul smell associated with anaerobic condition.
Qualitative analysisDetermination of the chemical composition of a sample
QuantaPlural of quantum.
Quantitative analysisChemical determination of the amounts or proportions of constituents in a substance.
QuantumA discrete packet of matter or energy, plural is quanta
Quantum numberValue used to describe the energy levels of atoms or molecules. There are four quantum numbers.
QuartzAn abundant mineral consisting of silicon dioxide(SiO2) with a hardness of 7 on the Mohs' scale.
QuenchStopping a reaction quickly, first used to refer to harden steel by quickly putting red-hot steel into cold water.
QuicklimeA common name for calcium oxide.
Radiant energyEnergy which is transmitted away from its source, for example, energy that is emitted when electrons transition down from one level to another.
RadiationEmitted energy in the form of rays, waves, or particles.
RadicalA species with an odd number of electrons; formerly called free radical.
RadioactiveSubstance containing an element which decays.
Radioactive tracerRadioactive element or compound added to a material to monitor its progress through a system.
RadioactivitySpontaneous emission of radiation as particles or photons from a nuclear reaction.
RadioisotopeContraction for words "radioactive isotope" of an element.
Raoult's LawRelation that states the vapor pressure of a solution depends on the mole fraction of solute added to the solution.
RatioThe 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 sewageSewage prior to receiving any treatment.
ReactantA starting material in a chemical reaction.
Reaction quotientQ-ratio of the concentration of products of a reaction to the concentration of the reactants.
Reaction rateThe speed at which chemical reactants form products.
ReactionA chemical change that forms new substances.
ReactivityThe degree to which a substance will respond to a stimulus or interact with another substance.
ReagentCompound or mixture added to a system to produce a reaction or test if one occurs.
Real gasGas that does not behave as an ideal gas because its molecules interact with one another.
ReceptorProtein molecules on the surface of cell membranes used for communication between cells.
RecorderA 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 propagationThe principle that electromagnetic radiations like light travel in straight lines.
RecyclingTo 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 indicatorCompound that changes color at a specific potential difference.
Redox reactionSet of chemical reactions involving reduction and oxidation
Redox titrationTitration of reducing agent by an oxidizing agent or vice versa.
ReducingThe gain of electrons by an atom, ion, or molecule.
ReductionChemical reaction in which an atom or molecule gains an electron; decrease in positive valence; addition of hydrogen to a molecule.
Reduction reactionA reaction in which a substance gains at least one electron.
Reduction treatmentThe 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.
RefrigerantA chemical used in refrigeration, to keep substances cool.
RegelationThe 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 densityRatio of density of a substance to the density of water.
Relative errorUncertainty of a measurement compared to the size of the measurement.
Relative standard deviationMeasure of precision of data, calculated by dividing standard deviation by the average of data values.
Relative uncertaintyRelative error; uncertainty of a measurement compared to the size of the measurement.
Residual chlorineChlorine remaining in water or wastewater at the end of specified contact period as combined or free chlorine.
ResidueMatter remaining after evaporation or distillation or an undesirable reaction byproduct or a recognizable portion of a larger molecule.
ResistanceThe 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.
ResistorA component of an electrical circuit intended to offer resistance to electrical current flow.
Resonance structurePossible structures of a molecule for which more than one electron-dot structure can be written, which differ in the bond pairs between atoms.
ResonanceAverage of two or more Lewis structure, differing in the position of electrons.
Reverse osmosisFiltration method that works by applying pressure on one side of a semipermeable membrane
Reversible reactionChemical reaction in which the products act as reactants for the reverse reaction.
RNARibonucleic acid, a molecule which codes for amino acid sequences.
RoastingMetallurgical process in which a sulfide ore is heated in air to form a free metal or metal oxide.
Room temperatureTemperature that is comfortable for humans, typically around 300 K.
RTAbbreviation for room temperature; ambient temperature that is comfortable for humans.
Rust preventativeA compound or formulated system used for coating metal surfaces to produce a film which protects against rust formation
SaccharinA 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.
SaltAny 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 bridgeConnection containing a weak electrolyte located between the oxidation and reduction half cells of a galvanic cell.
Salt thickeningThe 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.
SaponificationReaction 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 fatLipid containing only single C-C bonds.
Saturated solutionChemical solution containing the maximum concentration of dissolved solute for that temperature.
ScaleThe 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 equationExplains 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 lawGeneral 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 methodSystem of acquiring knowledge and solving problems through observation and experimental testing of hypotheses.
Second quantum numberℓ, the quantum number associated with the angular momentum of an atomic electron.
SedimentationThe 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-metalElement with a partially filled p orbital, causing it to exhibit properties intermediate between those of metals and nonmetals.
Settleable solidsParticles of debris and fine matter heavy enough to settle out of wastewater.
Settled sewageSewage from which most of the settleable solids have been removed by sedimentation.
SewageThe total of organic waste and wastewater generated by residential and commercial establishments.
ShellWhere the electrons generally are. These shells are composed of 4 types of electron subshells: s, p, d and f subshells.
SI UnitStands for Systeme International d'Unites, a international system which established a uniform set of measurement units.
SISystem Internationale, the standard metric system of units.
Sigma bondCovalent bonds formed by overlapping of outer orbitals of adjacent atoms.
Significant digitThose that can be accurately measured. An answer can have no more significant digits than the least number of them in the data.
SilicaSilica is the common name for silicon dioxide, SiO2.It exists in nature as crystalline quartz.
Simplest formulaRatio of elements in a compound.
Single bondWhen an electron pair is shared by two atoms.
Single displacement reactionChemical reaction in which an ion of one reactant is exchanged for the corresponding ion of another reactant.
Size of atomCan 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 nucleusWas measured by Lord Rutherford using the scattering patterns of alpha particles passing through gold foil. It is 10-15 meter.
Skeletal structureTwo-dimensional graphic representation of atoms and bonds in a molecule using element symbols and solid lines for bonds.
SludgeThe 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 conditioningA process employed to prepare sludge for final disposal, e.g., thickening, digesting, heat treatment or other procedures.
Sludge digestionThe 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 disposalThe final disposal of solid wastes including the use of sewage sludge as fertilizers and soil builders, and fill for low-lying lands.
Sludge thickeningThe increase in solids concentrations of sludge in the sedimentation of digestion tank.
SlurryA watery mixture or suspension of solids.
SmogA fog containing fumes, or a photochemical haze caused by the action of ultraviolet radiation on hydrocarbons and NOx from automobile exhaust.
Soda ashA common water treating chemical, sodium carbonate.
Softeningthe removal of hardness—calcium and magnesium—from water.
SoilIn the surfactant world - any material, solid, liquid or paste contaminant adsorbed onto a substrate.
SolA liquid colloidal dispersion; a fluid colloidal system in which solid particles are dispersed in a liquid colloidal solution.
SolderAn alloy of lead/tin used for making permanent electrical connections between parts and wire.
SolidState of matter characterized by high degree of organization, with a stable shape and volume.
SolidificationPhase change that results in formation of a solid.
SolubilityThe maximum amount of a substance that will dissolve in a given amount of solvent at a given temperature.
Solubility productKsp, the equilibrium constant for a chemical reaction in which a solid ionic compound dissolves to yield its ions in solution.
Soluble oilAn oil that readily forms a stable emulsion or colloidal suspension in water.
SoluteThe substance (solid, liquid, or gas) dissolved in a solution, for example, the salt in saltwater.
SolutionA mixture of two or more in which two or more materials are dissolved in another material.
SolventThe substance present in the largest amount in a solution; often the liquid component.
SoundA disturbance that travels through air, land, water that can be heard.
Specific gravityA comparison by weight to an equal volume of pure water, at a standard temperature.
Specific heatThe amount of heat it takes for a substance to be raised 1°C.
Specific heat capacityAmount of heat needed to raise the temperature of a substance per unit mass.
Spectator ionIon found in the same amount on both the reactant and product sides of a chemical reaction that does not affect equilibrium.
SpectrometerAn instrument for measuring the emission or absorption of light of a particular wavelength.
SpectrophotometerTool that measures the absorption or emission of electromagnetic radiation.
spectroscopyThe 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.
SpectrumCharacteristic wavelengths of electromagnetic radiation emitted or absorbed by an object or substance.
SpinThe 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 fissionSpontaneous splitting of an atomic nucleus into two smaller nuclei and usually neutrons, accompanied by the release of energy.
Spontaneous processProcess which can occur without any energy input from the surroundings.
Spontaneous reactionA reaction that will proceed without any outside energy.
Spontaneous changeChanges that occur on their own.
Standard hydrogen electrodeSHE, the standard measurement of electrode potential for the thermodynamic scale of redox potentials.
Standard oxidation potentialPotential 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 potentialPotential 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 solutionA solution with a precisely known concentration.
Standard temperature and pressureSTP, 273 K (0° Celsius or 32° Fahrenheit) and 1 atm pressure.
StandardReference used to calibrate measurements.
Standardized solutionA solution containing a known, precise concentration of an element or chemical compound, often used to calibrate analytical chemistry measurement devices.
State of matterHomogeneous phase of matter (e.g., solid, liquid).
State propertyA 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 matterSolid, liquid, gas and plasma. Plasma is a "soup" of disassociated nuclei and electrons, normally found only in stellar objects.
Steam distillationDistillation process in which steam or water is added to lower boiling points of compounds.
SteelAn alloy of iron that contains carbon.
StereochemistryThe spatial arrangement of atoms in molecules or compounds and the relation of spatial arrangement to the substanceis properties.
StereoisomerTwo 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 numberNumber of atoms bonded to a central atom of an molecule plus number of lone electron pairs attached to the central atom.
SteroidCompounds containing a 17-carbon, four-ring system.
Stock solutionConcentrated solution intended to be diluted to a lower concentration for actual use.
StoichiometryThe study of the relationships between amounts of products and reactants.
Storm sewageLiquid flowing in sewers during or following a period of heavy rainfall.
STPStandard temperature and pressure. This is 0°C and 1 atm.
StratosphereThe 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 acidAcid that completely dissociates into its ions in aqueous solution.
Strong baseBase that completely dissociates into its ions in aqueous solution (e.g., NaOH).
Strong electrolyteElectrolyte that completely dissociates in aqueous solution.
SublimationThe direct conversion of a solid to a gas.
SubshellSubdivision of electron shells separated by electron orbitals (e.g., s, p, d, f).
SubstituentAtom or functional group that replaces a hydrogen atom in a hydrocarbon.
Substitution reactionChemical reaction in which a functional group or atom is replaced by another functional group or atom.
SubstrateMedium on which a reaction occurs or reagent that offers a surface for absorption.
SulfationThe process by which an alcohol, such as lauryl alcohol, is reacted with sulfur trioxide (or chlorosulfonic acid) to give an alkyl sulfuric acid.
SulfonationThe process by which a material such as an alkylate is reacted with sulfur trioxide to give a sulfonic acid.
SuperconductivityA 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.
SupercriticalAbove the critical point; above critical temperature or pressure.
SupernateThe liquid result of a precipitation reaction.
Supersaturated solutionA solution that temporarily contains more solute than the saturated amount at some temperature.
SupersaturatedSupercooled; condition in which a liquid has been cooled to a temperature below which crystallization normally occurs, yet without solid formation.
Surface tensionThe property, due to molecular forces in the surface film, that tends to contract the liquid into a form having the least surface/volume ratio.
SurfactantA 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.
SuspensionHeterogeneous mixture of solid particles in a fluid.
SynthesisDescribes when a molecule consists of two or more smaller ones.
Synthesis reactionDirect combination reaction; chemical reaction in which two or more species combine to form a more complex product.
TaxolA 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.
TemperatureMeasure of how warm or cold a substance is.
Tensile strengthThe resistance of a substance to any force used to tear it apart.
TeratogenA substance that causes fetal abnormalities.
TermEach compound or element in a chemical equation.
Tertiary treatmentProcess 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.
TetrahedralMolecular geometry in which a central atom form four bonds directed toward the corners of a regular tetrahedron.
Texas carbonA carbon atom that forms five covalent bonds, forming a structure resembling a star.
Theoretical yieldQuantity of product that would be obtained if the limiting reactant in a reaction reacted completely.
TheoryA principle that explains a body of facts and the laws based on them.
Thermionic emissionThe boiling off of electrons from heated metals. It gives a source of electrons for cathode ray tubes.
ThermistorA semiconductor whose resistance will vary with temperature.
ThermodynamicsThe study of temperature, pressure, volume, and energy flow in chemical reactions.
Thermosetting plasticA polymer that is made irreversibly rigid upon heating.
ThickenerA 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 groupFunctional group containing a sulfur bound to a hydrogen, -SH.
ThiolAn organic sulfur compound consisting of an alkyl or aryl group and a sulfur-hydrogen group; R-SH.
TinctureAn extract of a sample into a solution, usually with alcohol as the solvent.
TitrantSolution of known concentration used in a titration to determine the concentration of a second solution.
TitrationA 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.
TorrUnit of pressure equal to 1 mm Hg or 1/760 standard atmospheric pressure.
ToxicityThe 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 isomerIsomer in which functional groups occur on opposite sides of the double bond.
Transition intervalConcentration range of chemical species that can be detected using an indicator.
Transition metalElement from the B group of the periodic table characterized by having partially filled d electron orbital sublevels.
Translational energyEnergy of motion through space.
TransmuteTo change from one form or substance into another.
Treatment efficiencyUsually refers to the percentage reduction of a specific or group of pollutants by a specific wastewater treatment step or treatment plant.
TriadA group of three elements whose chemical and physical properties aresomewhat related.
Triple pointTemperature and pressure at which the solid, liquid, and vapor phase of a substance coexist at equilibrium with each other.
TritiumA rare isotope of hydrogen with one proton and two neutrons.
TroposphereThe lowest part of the earth's atmosphere, extending from the surface of the planet to the bottom of the stratosphere.
TurbidimeterAn 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 effectThe scattering of a beam of light as is passes through a colloid.
Ultraviolet radiationIonizing electromagnetic radiation with a wavelength between 100 nm and 400 nm. Sometimes called black light.
UN IDA four-digit code used to identify dangerous or flammable chemicals. United Nations Identifier
UN numberA UN ID used for the transport of dangerous materials.
UnitA 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 cellThe smallest part of a crystal that could be used to create the whole crystal.
Universal gas constantUsually 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 indicatorA mixture of pH indicators used to measure pH over a wide range of values.
Universal solventA 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.
UnsaturatedAny 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 fatA lipid that contains no carbon-carbon double bonds.
Unsaturated solutionA solution in which solute concentration is lower than its solubility. All solute present dissolves into the solution.
Unsulfated mattersee - UNREACTED
VacuumA volume containing little to no matter (no pressure).
ValenceThe 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 theoryExplanation of bonding between two atoms as a result of the overlap of half-filled atomic orbitals.
Valence electronOuter electron most likely to participate in bond formation or a chemical reaction.
Valence shell electron pair repulsion theoryMolecular model that predicts geometry of atoms in a molecule by minimizing electrostatic forces between valence electrons around a central atom.
Van der Waals equationAn equation for non-ideal gasses that accounts for intermolecular attraction and the volumes occupied by the gas molecules.
Van der Waals forceWeak 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 radiusHalf the distance between two unbonded atoms in a state of electrostatic balance.
VaporAnother name for a gas.
Vapor pressurePressure 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.
VaporizationPhase transition from the liquid phase to gas phase.
VectorA geometric object that has both magnitude and direction.
VelocitySpeed of an object; the change in position over time.
VentingProviding an opening for the discharge of gases or the relief of pressure.
ViscosityThe 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 indexThe relationship of viscosity to temperature of a fluid. High viscosity index fluids will display less change in viscosity with temperature.
Visible lightElectromagnetic radiation that can be perceived by the human eye, usually from 380 nm to 750 nm (400 to 700 nm).
VolatileA substance which is easily vaporized.
Volatile solidThe quantity of solid in water, wastewater or other liquids, lost on ignition of the dry solids at 600 °C.
VolatizeTo make volatile; to cause to pass off in vapor.
VoltA unit of electrical potential.
VoltageThe electrical pressure (electromotive force) that makes current flow through a conductor.
VolumeThe space occupied in three dimensions.
Volumetric flaskType of chemistry glassware used to prepare solutions of known concentration.
VSEPRsee Valence Shell Electron Pair Repulsion Theory
VulcanizationThe process for changing rubber from a weak material into a hard, strong material, usually by heating with sulfur.
WashdownWater resulting from cleaning of equipment, walls, floors, etc., within a plant.
Water gasA combustion fuel that contains hydrogen gas and carbon monoxide.
Water of crystallizationWater the stoichiometrically bound in a crystal.
Water of hydrationWater stoichiometrically bound in a compound, forming a hydrate.
WaterA compound formed by one oxygen atom and two hydrogen atoms. Usually this refers to the liquid form of the molecule.
WattThe practical unit of electrical power.
WaveA signal which propagates through space, much like a water wave moves through water.
WavefunctionA function that describes the probability of the quantum state of a particle in terms of spin, time, position, and/or momentum.
WavelengthThe 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 dualityThe concept that photons and subatomic particles exhibit properties of both waves and particles.
WaxA lipid consisting of chains of esters or alkanes derived from fatty acids and alcohols.
Weak acidSubstances capable of donating hydrogen but do not completely ionize in solution.
Weak baseSubstances capable of accepting hydrogen but do not completely ionize in solution.
Weak electrolyteAn electrolyte that does not completely dissociate into its ions in water.
wedge-and-dash projectionMolecule representation using three types of lines to show three-dimensional structure.
WeightThe measures of the earth's gravitational pull on a object.
WettingThe coating of a contact surface with an adherent film of liquid.
Wire gaugeWire size, measured in diameter.
Word equationA chemical equation expressed in words rather than chemical formulas.
WorkForce multiplied by distance or the amount of energy needed to move a mass against a force.
Working solutionA chemical solution prepared for use in a lab, usually by diluting a stock solution.
Writing and BalancingStarting Materials and Products have the same kinds of elements and same numbers of atoms.
X-rayElectromagnetic radiation of high frequency and short wavelength (ranging from 10-11 to 10-9 meters).
X-ray crystallographyA 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.
YieldIn 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.
Zaitsev ruleRule in organic chemistry that states alkene formation from an elimination reaction will produce more highly substituted alkenes.
ZeoliteA 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 processAn 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.
ZwitterionAn ion that has a positive and negative charge on the same group of atoms. It is also called dipolar ion.
ZymogenAn inactive biomolecule that is a precursor to an enzyme.


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