Question

How and why does the valency of an element vary as you go : (a) from left to right along a period. (b) down the group ?

Answer 1

Variation of valency in the periodic table:

Variation in a period: The number of valency electrons increases from 1 to 8 on moving across a period, the valency of the elements with respect to hydrogen and chlorine increases from 1 to 4 and then decreases to zero.

Variation in a group: On moving down a group, the number of valence electrons remains same and therefore, all the elements in a group exhibit same valency.