Question

What is the periodic trend in the variation of valency while going down a group?

Explain your answer with reference to the group 1, group 2 and group 18.

Answer 1

(1) The valency of an element is determined by the number of valence electron in the outermost shell of an atom of an element.

(2) All the elements in a group have the same number of valence elements. Therefore, elements in the same group should have the same valency. For example, the elements of group 1 (H, Li, Na, K etc.) contain only one valence electron. the valency of elements of group 1 is one. Similarly for group 2, (Be, Mg, Ca) contain two valence electrons, the valency of elements of group 2 is two.

(3) The elements of group 18 1 (Ne, Ar) contain 8 electrons (exception, Helium contain 2 electrons). Since the octet is completed their valency is zero.

Element	K	Na	Rb	Cs	Li
Atomic radius (pm)	231	186	244	264	152