Question

what are the reasons for the different chemical behaviour of the first member of the groups of elements in the s and p block compared to that of the subsequent member in the same group?

Answer 1

heya...

Reasons..
1. It is the smallest element of the group..
2. absence of D orbitals..
3. Follows diagonal relationship.

Answer 2

Ans: Because of their smaller size and absence of d-orbitals the first members of s, p-block elements posses different properties. Ex: Nitrogen can show maximum valency of 3 it cannot expands it valency beyond 3 but phosphorus same group of nitrogen can show valency of 5 in PCl5 due to presence of d-orbitals in phosphorus.