# How to Calculate Bond Order

Bond order is defined in simple words as the number of bonds formed between two atoms. This article covers the basic concept, application, and calculation of this order.

Ashlesha Bhondwe

Bond Order Formula

This concept is commonly used in molecular orbital theory. According to this concept, bond order is half of the difference between the number of bonding electrons and the number of antibonding electrons.

**B.O. = ½ (number of bonding electrons - number of antibonding electrons)***n, l, m, s*, and they must be different for the electrons to have opposite spins.

Calculations

*For C*_{2}-You must know the number of electrons in the bonding and antibonding orbitals. A clue to find this out is to draw an orbital structure, and determine the number of electrons in each orbit. In the case of C

_{2}, there is an extra electron in the bonding orbital. Thus, after applying the formula provided above,

B.O. = ½ (9-4) = 2.5

*For N*_{2}+ and N_{2}-The value for both of these is 2.5, as in both cases there is an unpaired electron either in the bonding or antibonding orbital, reducing the value by half.

**For Benzene**Benzene is an aromatic cyclic compound, and hence, has resonance structures. In this compound, 6 pi electrons are shared by 6 carbon atoms; every carbon has half a pi bond and one sigma bond. Thus, the bond order of benzene is 1.5 for each bond.

For a Diatomic Molecule

Linus Pauling derived a formula to determine the bond order, and it was later realized that this formula can only be applied to diatomic molecules. It is given as,

Here, R

d

'b' is a constant, calculated by Pauling as 0.353.

**B.O. (S**_{ij}) = exp[R_{ij}- d_{ij}**/ b]**Here, R

_{ij}stands for experimentally measured bond length,d

_{ij}stands for the single bond length, and'b' is a constant, calculated by Pauling as 0.353.