Periodic Trends of Atomic Radius

• An atom gets larger as the number of electronic shells increase; therefore the radius of atoms increases as you go down a certain group in the periodic table of elements.
• In general, the size of an atom will decrease as you move from left to the right of a certain period.

Figure 1: Periodic Trend in atomic radii

Vertical Trend

EXCEPTIONS: Because the electrons added in the transition elements are added in the inner electron shell and at the same time, the outer shell remains constant, the nucleus attracts the electrons inward. The electron configuration of the transition metals explains this phenomenon. This is why Ga is the same size as its preceding atom and why Sb is slightly bigger than Sn.