Explain periodicity of valence or oxidation state of s and p block elements.

Explanation

a )Vacation of valence across a period : As we more across a period from left to right , the number of valence electrons increase from 1 to 8 The valence with respect to hydrogen or chlorine first increases from 1 to 4 and then decrease from 4 to 0 . However, valence with respect to oxygen increase from 1 to 7 Ex : Element , of 2nd and 3rd periods.
b) Vacation of valence down a group : on moving down a group , the number valence electrons remain the same , and therefore , the elements in a group show the same valiancy . Examples : All the elements of group 1 are monovalent ( valiancy = 1 ) and all the elements of group 2 are divalent ( valiancy = 2 )