Molecular orbital theory was proposed by F.Hund and R.S. Mullikan in 1930 which was later developed by Lennard-Jones and Charles Coulson. This theory explains the formation of covalent bonding through entirely different approach, according to this theory atomic orbitals combine to form molecular orbitals.
Salient features of molecular orbital theory:
1. When atomic orbitals combine, they form molecular orbitals.
2. A molecular orbital is a region in space where the probability of finding electrons is maximum in a molecule.
3. When two atomic orbitals combine, they form two molecular orbitals called bonding molecular orbital and antibonding molecular orbital.
4. A bonding molecular orbitals has lower energy and an antibonding molecular orbitals has higher energy.
5. Molecular orbitals are polycentric i.e., the electrons move under the influence of all the nuclei.
6. The shapes of the molecular orbitals depend on the shapes of combining atomic orbitals.
7. Only those atomic orbitals having similar energy and proper symmetry can combine to form molecular orbitals.
8. The bonding molecular orbitals are represented as σ or π orbitals while antibonding molecular orbitals are represented as σ* or π* orbitals.
9. Each molecular orbital can accommodate a maximum of two electrons with opposite spins.
10. Electrons are filled in the molecular orbitals according to aufbau principle, Hund’s rule and Pauli’s exclusive principle.
