# What is the trend in Atomic Radii? Which elements have a bigger Radius?

Oct 22, 2016

Down a group, the atomic radius increases. Across a period, the atomic radius decreases.

#### Explanation:

1. Down a group
• The number of energy levels increases by 1 as we go down a group. This makes the atom larger.
• An increasing number of electron shells increases the nuclear shielding. Thus, outer e- are protected from the positive charge of the nucleus by filled inner e- shells.
• The nuclear charge (ie. the number of protons) does increase down a group and the nucleus becomes more positive. However, the increased nuclear shielding protects the outer e- from the increased pull.

For example, Rb has a bigger atomic radius than Na.

2. Across a period.