The bond order, which is the number of bonds between any two given atoms, is calculated using the formula: Bond order = (Bonding electrons - Anti-bonding electrons) / 2.The Lewis structures of atoms form the basis for calculating the bond order.
The bond order of a molecule that has multiple Lewis structures is calculated as the average of these Lewis structures. For example, sulfur dioxide has three bonds: a single bond for sulfur oxide in one Lewis structure and a double bond for sulfur oxide in a different Lewis structure within the molecule. This gives a bond order of 1.5, which is the average value of the three bonds.
In molecular orbital theory, bond orders are calculated by assuming that a pair of electrons in a bonding molecular orbital form one bond while a pair of electrons in a non-bonding molecular orbital nullify the effect of one bond.
For example, the bonding molecular orbital of the oxygen molecule has eight valence electrons while the anti-bonding molecular orbital of the same molecule has four valence electrons. So, the bond order of the oxygen molecule can be calculated as follows:
Bond order = (Bonding electrons - Anti-bonding electrons) / 2
- Bond order = (8 - 4) / 2
- Bond order = 4 / 2
- Bond order = 2