Explain why cations are smaller and anions larger in radii than their parent atoms?
Cations are always smaller in radii than their parent atoms because by the loss of one or two electrons, effective nuclear charge increases. Due to this, forces of attraction of nucleus for electrons increases and hence, ionic radii decreases. On the other hand, anions are always larger in radii than their parent atoms because by the addition of one or two electrons effective nuclear charge decreases. Due to this, forces of attraction between nucleus and valence shell electrons decreases and hence, ionic radii of anion increases.