How do the following properties change in group - 1 and in the third period? Explain with example.
(a) Atomic radius.

Explanation

Atomic radius: As we move from top to bottom of group - 1 elements the atomics radius gradually increase. As we move from top to bottom is graup -1 elements the number of orbits filling with electrons increases. So the atomic radius increases from top to bottom in gruou-1 elemetns.
In a period from left to rigth the atomic radius gradually decreases.
In the 3rd period, the differentiating electron enters into the same 3rd orbit. The electrons entering into the same orbit have less shielding power but the nuclear charge is increasing. COnsequently the effective nuclear charge increases. So atomic radius decreases.