Features

1. When two atomic orbitals combine or overlap, they lose their identity and form new orbitals. The new orbitals formed are called molecular orbitals.

2. Only those atomic orbitals can combine to form molecular orbitals which have comparable energies and proper orientations.

3. The number of molecular orbitals formed is equal to the number of combining atomic orbitals.

4. When two atomic orbitals combine, they form two new orbitals called ‘bonding molecular orbital’ and ‘antibonding molecular orbital’.

5. The bonding molecular orbital has lower energy and hence greater stability than the corresponding antibonding molecular orbital.

6. The bonding molecular orbitals are represented by σ,π,δ  and antibonding are represented by σ*,π*,δ* .

7. The shapes of the molecular orbitals formed depend upon the type of the combining atomic orbitals.

8. Filling of MO takes place according to following rules :

• Aufbau principle, Pauli’s exclusion principle,
• Hund’s rule of maximum multiplicity.