Explain why cations are smaller and anions larger in radii than their parent atoms?

Explanation

A cation is formed by the loss of one or more electrons from the gaseous atom. With the loss of electrons from an atom, the magnitude of the nuclear charge remains same while the number of electrons decreases. As a result, the same nuclear charge now acts on lower number of electrons and therefore, the effective nuclear charge per electron increases. As a result, electrons are more strongly attracted and are pulled towards the nucleus and therefore, the size decreases. The anion is formed by the gain of one or more electrons and therefore, the number of electrons increases while the magnitude of nuclear charge remains same. As a result, the electrons are less tightly held by the nucleus and therefore, the size increases.