Atomic radius is half the distance between adjacent atoms of the same element in a molecule.
- In general, the atomic radius decreases as we move from left to right in a period, and it increases when we go down a group.
- There are some small exceptions, such as the oxygen radius being slightly greater than the nitrogen radius. Within a period, protons are added to the nucleus as electrons are being added to the same principal energy level.
(a) Li, Be, F, N
F < N < Be < Li as the atomic radii decreases along a period.
These elements are in the same period and atomic radii decrease from left to right.
(b) Cl, At, Br, I
CI < Br < I < At as the atomic radii increase down a group.
These elements are in the same group and are atomic radii increases from top to bottom.