(a) Define the following terms:
(i) Valency, (ii) Atomic size
(b) How do the valency and the atomic size of the element vary while going from left to right along a period in the modern periodic table?

Explanation

(i) Valency. The combining capacity of an element is called its valency.
`*` The valency of an element is determined by the number of valence electrons present in the atom of the element.
`*` The number of electrons lost or gained or shared by one atom of an element to achieve the nearest inert gas configuration give the valency of the element.
(ii) Atomic size. The atomic size of an atom is the distance between the centre of the nucleus and outermost electron shell of an isolated atom.
(b) - On moving from left to right along a period in the modern periodic table, the valency of elements increases from 1 to 4 and then decreases to zero.
- On moving from left to right in a period of the periodic table, the size of the atoms decreases.