Explain why cation is smaller and anion is larger in radii than their parent atoms.

Explanation

When an electron is removed from a neutral atom, cation is formed . The nuclear charge in both the cation and in its parent atom is the same . But the number of electrons in the cation are less than in its parent atom.
Hence, the nuclear attractions, in a cation will be more than in its parent atom. As a result of which the electron colud of cation shrinks. Hence the size of a cation is always smaller then its parent atom.

When an electron is added to a neutral atom, anion is formed. The nuclear change in both the anion and in its parent atom is the same. But, the number of electrons in the anion are more than in its parent atom. Hence the nuclear attractions, in the anion will be less then in its parent atom. As a result of which the electron cloud expands. Hence, the size of anion is always greater than its parent atom.