Explain the formation of H2 molecule on the basis of valence bond theory.

Explanation

Consider two hydrogen atom A and B approaching each other. Their nuclei are `N_(A)" and "B_(B)` respectively. Their eletrons are represented by `e_(A)" and "e_(B)`. When two atoms are away from each other, there is no interaction between them. As these two atoms approach each other, new attractive and repulsive forces begin to operate.
(i) Attractive force arise between:
(a) nucleus of one atom and its own electrons that is `N_(A)-e_(A)" and "N_(B)-e_(B)`.
(b) nucleus of one atom each and electrons of other atom that is `N_(A)-e_(B), N_(B)-e_(A)`.
(ii) Repulsive forces arise between:
(a) electrons of two atoms like `e_(A)-e_(B)`
(b) nuclei of two atoms `N_(A)-N_(B)`

It has been experimentally observed that the magnitude of new attractive forces are more than the new repulsive forces. As a result, two atoms approach each other and potential energy decreases. so, two hydrogen atoms get bonded to form a stable molecule of `H_2`.