## How does atomic radius vary in group in the periodic table?

### Q.56:- (a) How does atomic radius vary in group in the periodic table? (b) Explain (i) Radius of cation is less than that of the atom. (ii) Radius of anion is more than that of the atom. (iii) In iso-electronic ion, the ionic radii decreases with increase in atomic number.

Answer:-
(a) Variation of atomic radius in a group:
On moving down the group there is an increase in the principal quantum number and therefore no. of electron shells increases and thus the atomic size increases. Thus the atomic radii of the element increases.
(b) (i) Radius of cation is less than that of the atom:
Since the cation is formed by losing of one or more electrons.
For example,
Na —> Na++ e
Thus the radius of Na+will be less than the Na.
(ii) Radius of anion is more than that of the atom.
Since the anion is formed by gaining one or more electron. Therefore, the atomic radius is larger than the corresponding atom.
(iii) In iso-electronic ions, atoms have same number of electrons but different magnitude of nuclear charges. As the nuclear charge increases ionic radius decreases.
For example. N3-, O2-, Fhave same No. of electrons = 10 but different ionic radii = 171, 140, 136 respectively.