Prove that the atomic radii is a periodic property.

Explanation

Atomic radius is the distance between the centre of its nucleus and the outermost shell containing the electron. Atomic radius is a periodic property.
(i) Variation in periods:
The atomic radius decreases while going from left to right in a period. As we move from left to right in a period, the nuclear charge increases by one unit in each succeeding element. But the number of the shell remains same. Hence, the electrons are attracted strongly by the nucleus. Hence the atomic radius decreases along the period.
In 2nd period `r_(Li)gtr_(Be)gtr_(B)gtr_(C)gtr_(N)gtr_(O)gtr_(F)`
(ii) Variation in a group:
The atomic radius of elements increases with increase in atomic number as we move from top to bottom in a group. The attraction of the nucleus for the electrons decreases as shell number increases. Hence atomic radius increases along the group.
In `1^(st)` group `r_(Li)ltr_(Na)ltr_(K)ltr_(Rb)ltr_(Cs)`
Hence, atomic radii is a periodic property.