Question

Atomic size decreases in a period and increases in a group why?

Answer 1

This is caused by the increase in the number of protons and electrons across a period. One proton has a greater effect than one electron; thus, electrons are pulled towards the nucleus, resulting in a smaller radius.Atomic radius increases from top to bottom within a group. This is caused by electron shielding.

Answer 2

Atomic size decreases from left to right in a period this is caused by increased in protons and electrons across period.

The increase in going down is that because of increase in Shelley of an atom