The net contribution of the electrons to the bond strength of a molecule is identified by determining the bond order that results from the filling of the molecular orbitals by electrons. The bond order is calculated by subtracting the destabilizing (antibonding) electrons from the stabilizing (bonding) electrons. Since a bond consists of two electrons, we divide by two to get the bond order.
The Correct Answer and Explanation is:
Correct answer:
The bond order is calculated using the formula:
Bond order = (Number of bonding electrons − Number of antibonding electrons) ÷ 2
Explanation:
Bond order is a concept used in molecular orbital (MO) theory to describe the stability and strength of a chemical bond within a molecule. It gives a quantitative value that reflects how strongly two atoms are bonded. The higher the bond order, the stronger and more stable the bond; the lower the bond order, the weaker and less stable the bond. A bond order of zero indicates that no bond exists between the atoms.
In molecular orbital theory, atomic orbitals from each atom combine to form new orbitals that are spread across the entire molecule. These new orbitals are either bonding orbitals or antibonding orbitals. Bonding orbitals are lower in energy and stabilize the molecule because they hold the nuclei of bonded atoms together through shared electron density. Antibonding orbitals, on the other hand, are higher in energy and destabilize the molecule because their electron density is located in regions that pull the nuclei apart.
To determine the bond order, we count the number of electrons in bonding molecular orbitals and subtract the number of electrons in antibonding orbitals. The difference is then divided by two because each bond is made up of a pair of electrons.
For example, in diatomic nitrogen (N₂), there are ten bonding electrons and four antibonding electrons. Applying the formula:
Bond order = (10 − 4) ÷ 2 = 3
This bond order of 3 corresponds to a triple bond, which explains why N₂ is a very stable molecule with a high bond dissociation energy. Understanding bond order helps chemists predict molecular stability, reactivity, and bond length.
