chemistry

VALENCE BOND THEORY

The basis of VBT is Schrodinger's wave equation i.e. wave mechanics. It explains shapes of covalent molecules and strength of covalent bonds.

•        This theory was proposed by Hietler and London and developed by pauling and slater.

Postulates: A bond is formed by the overlapping of two half-filled orbitals of two atoms.

•        The e s in the overlapping orbitals must be with opposite spins.

•        Strength of covalent bond will depend on the extent of overlapping i.e., greater the extent of overlapping, stronger is the bond formed and vice versa.

•        The direction in which overlapping orbitals are concentrated, the bond is formed in that direction. This explains directional nature of covalent bond and shape of orbital.

•        The molecule will be stable because the bonding electron density is in consideration along the inter nuclear axis and that electron density keeps the two atoms attracted to each other.

The extent of overlapping will depend on size of atom and nature of orbital. p – p > s – p > s – s

•        Smaller atoms involve in greater overlapping.

	Cl – Cl  >	Br – Br
	(p – p)	(p – p)