# What happens to ionic size across a period?

Mar 25, 2014

As a general rule the radius of the cation (+ ion) is smaller than the atomic radius of the original atom and the radius of the anion (- ion) is larger than the atomic radius of the original atom.

The trend across the periods, is that the ions are larger as you move to right to left on the periodic table.

For the Cations in period 2 (2nd row of the periodic table),
Boron ${B}^{+ 3}$ is smaller than Beryllium $B {e}^{+ 2}$ which is smaller than Lithium $L {i}^{+ 1}$

For the Anions in period 2 (2nd row of the periodic table),
Fluorine ${F}^{- 1}$ is smaller than Oxygen ${O}^{- 2}$ which is smaller than Nitrogen ${N}^{- 3}$.