The bond parameters of covalent bonds can characterize the properties of covalent bonds. Among them, the bond length, bond angle, and bond energy of covalent bonds are the three key parameters that describe their structural characteristics.
What is the Bond Length of Covalent Bonds?
The equilibrium distance between the two atomic nuclei that form a covalent bond is called the bond length of covalent bonds. The bond length of a homonuclear diatomic molecule is the sum of the covalent radii of the two atoms. X-ray diffraction, electron diffraction, and spectroscopy can all be used to measure bond lengths. The following lists some common covalent bond lengths in organic compounds. The data in the table show that when the bond type and bonding hybrid orbital change, the bond length of the covalent bond will also change.
Common Covalent Bond Length Table (pm)
| Compound | Bond | Bond Length | Compound | Bond | Bond Length |
| Methane | C-H | 109 | Alkanes | C-C | 154 |
| Ethylene | C-H | 107 | Alkenes | C=C | 134 |
| Acetylene | C-H | 105 | Alkynes | C≡C | 120 |
| Benzene | C-H | 108 | Acetonitrile | C-C | 149 |
| Thiourea | C=S | 164 | Propylene | C-C | 150 |
| Trimethylamine | C-N | 147 | Fluoromethane | C-F | 142 |
| Urea | C-N | 137 | Methyl chloride | C-CI | 177 |
| Acetonitrile | C≡N | 115 | Methyl bromide | C-Br | 194 |
| Methyl ether | C-O | 144 | Methyl iodide | C-I | 213 |
| Formaldehyde | C=O | 121 | Ethyl chloride | C-CI | 169 |
What is the Bond Angle of a Covalent Bond?
The angle between two chemical bonds formed by the same atom in a molecule is called the bond angle. Bond angles are often expressed in degrees. For example, water molecules are bent, and their bond angles are 104.5°; ammonia molecules are trigonal pyramids, and their bond angles are 107.3°; and methane molecules are regular tetrahedrons, and their bond angles are 109.5°. Because there are bond angles between chemical bonds, covalent bonds have directionality. The following lists the bond angles of some hydrocarbon compounds.
Bond Angles of Common Hydrocarbon Compounds
| Compound | Angle | Bond Angle | Compound | Angle | Bond Angle |
| Methane | ∠HCH | 109°28' | Propylene | ∠CCC | 180° |
| Ethylene | ∠HCC | 122°±2° | Benzene | ∠CCH | 120° |
| ∠HCH | 116°±2 | Cyclohexane | ∠CCC | 109°28' | |
| Acetylene | ∠HCC | 180° |
What are Bond Dissociation Energy and Average Bond Energy?
The energy consumed or released to break or form a bond in a molecule is called bond dissociation energy. Under standard conditions, the bond dissociation energy of a diatomic molecule is its bond energy, which is a measure of the strength of the chemical bond. For polyatomic molecules, since the bond dissociation energy of each bond is not always equal, the bond energy usually referred to actually refer to the average bond energy of such bonds.
For example, the bond dissociation energy of the four C-H bonds in a methane molecule is different. The first C-H bond dissociation energy is 439.3 kJ/mol, the second and third C-H bond dissociation energies are both 442 kJ/mol, and the fourth C-H bond dissociation energy is 338.6 kJ/mol. The average bond energy of the C-H bond is (439.3+442×2+338.6)kJ/mol/4=415.5 kJ/mol. obviously, using bond dissociation energy is more accurate than using average bond energy.
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