Question

The valencies of p block elements are equal to group number or 8 minus the group number. Therefore they show one lower valency and one higher valency. However, if we go to the bottom elements of any group, the compounds with lower valency are predominant whereas higher valency becomes rather uncommon. Explain.

Answer 1

It is due to Inert pair effect.It is increasing stability of oxidation states that are two less than the group valency for the heavier elements of groups 13,14 ,15 and 16.

Consider as an example thallium (Tl) in group 13 . The +1 oxidation state of Tl is the most stable, while Tl^III compounds are comparatively rare. The stability of the +1 oxidation state increases in the following sequence:

Al^I < Ga^I < In^I < Tl^I.