Reference Notes | Science
Valence Bond Theory (VBT)
Unit: Chemical Bonding and Shape of Molecules
Chemistry Class 12

The first quantum mechanical model to explain the nature and stability of a covalent bond was formulated by Hilter and London in 1927 and modified by Linus Pauling in 1931, who was awarded the Nobel prize for chemistry in 1954. This theory is called valence bond theory.

Postulates of Valence Bond Theory (VBT):

1. Overlapping of the outermost half-filled orbitals of the combining atoms form covalent bond.
2. The outermost half-filled orbitals should contain electrons with opposite spin.
3. The orbitals which are completely filled with electrons do not take part in the bond formation.
4. The strength of the bond is determined by the extent of overlap.
5. The greater is the overlapping of atomic orbitals, the stronger is the covalent bond formed.
6. The valency of an element is equal to the half-filled orbitals present in it.