Question

Arrange the elements N, P, O and S in the order of —

(i) increasing first ionisation enthalpy.

(ii) increasing non-metallic character.

Give reason for the arrangement assigned.

Answer 1

(i) S<P<O<N

Ionisation enthalpy increases from left to right in a period and decreases down the group. N has higher ionisation enthalpy than O due to extra stability of half-filled orbitals. Similarly, P has higher ionisation enthalpy than S due to half-filled orbitals.

(ii) P<S<N<O

Non-metallic character decreases down the group and increases from left to right in a period.