# Question #ecf1d

$\text{Veritas.........}$
It is a fact that ACROSS a Period, from left to right as we face the Table, atomic size decreases. The added electrons do not effectively shield the increasing nuclear charge, and atomic radii decrease. Down a Group, a column, of the Periodic Table, atomic size INCREASES, as a filled electronic shell tends to shield nuclear charge effectively. This contest between $\text{nucular charge}$ and shielding of that charge by filled electron shells tends to underlie the structure of the Periodic Table.