Question

Why does the stability of +5 oxidation state decrease on moving down the group 15?

Answer 1

1. Group 15 elements have the valence electron configuration ns² np³.
2. To achieve +5 oxidation state, all five valence electrons (2 from ns and 3 from np) are lost or shared.
3. Moving down the group, the ns² “inert pair” becomes less inclined to participate in bonding due to the inert pair effect.
4. The inert pair effect is the reluctance of the ns² electrons to get excited and form bonds, making +3 oxidation state more stable than +5.
5. This effect increases down the group because of poor shielding and increased nuclear charge on the ns electrons.
6. As a result, heavier elements like Sb and Bi prefer +3 oxidation state, while lighter elements (N, P) can achieve +5 state more easily.

Thus, stability of +5 oxidation state decreases due to the increasing inert pair effect and reluctance of ns² electrons to be involved in bonding on moving down the group.