Question

The bond order of a molecule is given by:
A.The difference between the number of electrons in the bonding and the antibonding orbitals.
B.Total number of electrons in the bonding and the antibonding orbitals.

Answer 1

The bond order in a molecule is equal to the number of bonds between the atoms and it is indicative of the stability of the molecule. The bond order does not apply to ionic bonds as it is not a proper bond but just a force of attraction between the atoms in the molecule.

Complete answer:
The term “bond order” was introduced by Linus Pauling and is defined as half of the difference between the number of bonding electrons and the antibonding electrons. The bond order is also indicative of the bond strength of the molecules and is extensively applied to the valence bond theory. Mathematically, the bond order can be represented as:
Bond order = $\dfrac{\text{no}\text{. of bonding electrons - no}\text{. of anti bonding electrons}}{\text{2}}$

Hence the correct option is A, The difference between the number of electrons in the bonding and the antibonding orbitals.

Note:
Generally the higher the bond order the stronger will be the bond. The concept of bond order is useful in molecular dynamics and bond order potentials. The magnitude of the bond order is associated with bond length as well. In molecules that have resonance or non-classing bonding bond order may not be integral but will be of fractional order. In benzene for example, the delocalized molecular orbitals contain 6 pi electrons over 6 carbons essentially yielding half a pi bond with the sigma bond for each pair of carbon atoms giving a calculated bond order of $1.5$.