Bond Length:
The distance between the centers of two nuclei of atoms connected by a chemical bond is known as ‘bond length’.
It is very small to measure by X-ray diffraction, spectroscopic methods etc. Angstrom (Å) unit is used (1 Å = 10-8 cm.).
If RAB = inter-atomic distance of two atoms A and B, rA = covalent radius of A and rB = covalent radius of B; then
| Atom | Single bond covalent radius | Double bond covalent radius | Triple bond covalent radius |
| H | 0.33 | --- | --- |
| C | 0.77 | 0.67 | 0.60 |
| O | 0.73 | 0.55 | --- |
| N | 0.74 | 0.62 | 0.55 |
| S | 1.04 | 0.94 | --- |
| Cl | 1.00 | --- | --- |
Bond Angle:
The angle between the directions of two bonds in a molecule is called the ‘bond angle’.
| Bond hybridization | Geometry | Bond angle |
| sp | Linear | 1800 |
| sp2 | Triangular | 1200 |
| sp3 | Tetrahedral | 109028´ |
Bond angle depend upon factors, (i) charge distribution, (ii) geometry of the molecules, (iii) symmetry, (iv) hybridization etc.
| Species | Angle | Species | Angle |
| CH4 | H-C-H, 109o | SO3 | O-S-O, 120o |
| NH4+ | H-N-H, 109o | NO3- | O-N-O, 120o |
| H2O | H-O-H, 105o | NH3 | H-N-H, 107o |
Bond Energy:
Bond energy is defined as the energy required to split the molecule into atoms.
It may be determined (i) by measurement of equilibrium constants for dissociation of molecules at high temperature, (ii) from the spectrum.
It depends on types of bonding- single, double or triple bonds.
The greater the difference in bond energies, the greater is the polarity and hence greater will be the difference in electronegativity values of the atoms forming the molecule.
| Bond | Calculated mean bond energy, kcal/mole | Experimental | Difference | Electronegativity difference |
| H-O | 59 | 108 | 49 | 1.4 |
| H-Cl | 79 | 103 | 24 | 0.9 |
| Cl-O | 43 | 49 | 6 | 0.5 |