The ionic radius of the elements exhibits trends in the periodic table.
Ionic Radius and Group
As you move down a group in the periodic table, additional layers of electrons are being added, which naturally causes the ionic radius to increase as you move down the periodic table.
Ionic Radius and Period
As you move across a row of period of the periodic table, the ionic radius decreases for metals forming cations, as the metals lose their outer electron orbitals. The ionic radius increases for nonmetals as the effective nuclear charge decreases due to the number of electrons exceeding the number of protons.
Ionic Radius and Atomic Radius
The ionic radius is different from the atomic radius of an element. Positive ions are smaller than their uncharged atoms. Negative ions are larger than their atoms.