Valence Bond Approach VB

This was first developed by Heitler and London in 1927 and later extended by Pauling and Slater in 1931. It is assumed that atoms complete with electrons, come together to form the molecule. The atoms retain their individuality and the bond is formed due to the interaction of valence electrons as the atoms approach each other. 

Valence bond theory states that a chemical bond can be formed by the overlap of atomic orbitals. Overlap means, the two orbitals share a common region in space. 

The total number of electrons in both the orbitals is not more than two. The covalent bond is formed by pairing and resultant neutralisation of opposite electron spins. 

The VB approach may be illustrated considering the formation of hydrogen molecule. 

The two hydrogen atoms when infinitely apart, exert no influence over each other. Although the two hydrogen atoms are identical, for convenience sake, the two electrons may be labelled 1 and 2 and the nuclei A and B. 

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