Question

Briefly describe the valence bond theory of covalent bond formation by taking an example of
hydrogen. How can you interpret energy changes taking place in the formation of dihydrogen

Answer 1

The valence bond theory was put forward by Heitler and London in 1927. It was later improved
and developed by L. Pauling and J.C. Slater in 1931. The valence bond theory is based on the
knowledge of atomic orbitals and electronic configurations of elements, overlap criteria of atomic
orbitals and stability of molecule.
The main points of valence bond theory are
(i) Atoms do not lose their identity even after the formation of the molecule.
(ii) The bond is formed due to the interaction of only the valence electrons as the two atoms come
close to each other. The inner electrons do not participate in the bond formation.
(iii) During the formation of bond, only the valence electrons from each bonded atom lose their identity. The other electrons remain unaffected.
(iv) The stability of bond is accounted by the fact that the formation of bond is accompanied by
release of energy. The molecule has minimum energy at a certain distance between the atoms
known as intemuclear distance. Larger the decrease in energy, stronger will be the bond formed