Atomic and Ionic Radii

Compared with the alkali metal directly to their left in the same period, the Group 2 elements have distinctly smaller atomic and ionic radii — a consequence of the extra proton (higher nuclear charge) pulling the same-shell electrons in more tightly, even though the electron is entering the same shell as before. Within Group 2 itself, however, the familiar trend holds: both atomic and ionic radius grow steadily as atomic number increases down the group, since each successive element adds a whole ne …