Question

Phosphorus form both PCl3 and PCl5 but nitrogen forms only NCl3 why?

Answer 1

covalency of Nitrogen is 4 , hence it can not form 5 bonds

Answer 2

Explanation:

Atomic number of phosphorus is 15 and its electronic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{3}$.

Whereas atomic number of nitrogen is 7 and its electronic configuration is $1s^{2}2s^{2}2p^{3}$.

Thus, we can see that phosphorus can expand its oxidation state as it has empty 3d orbitals also. On the other hand, nitrogen does not has any empty orbitals so it cannot expand its oxidation state.

As a result, nitrogen forms only $NCl_{3}$ and cannot form $NCl_{5}$.