The ionic radius of a nonmetal is generally smaller than its atomic radius when the nonmetal gains electrons to become an anion. This occurs because when nonmetals, like chlorine or oxygen, gain electrons, they experience increased electron-electron repulsion within their electron cloud, which can lead to a somewhat larger ionic radius than the original atomic radius. However, the ultimate effect is that even though the ionic radius can be larger due to added electrons, it is still typically smaller than the radius of a metal cation.
In summary:
- When a nonmetal gains electrons to form an anion, its ionic radius may be larger than its atomic radius due to added electron-electron repulsion, but it usually remains smaller than metal cations (which are smaller than their atomic radii due to loss of electrons and reduced electron-electron repulsion).
- If a nonmetal loses electrons (which is less common), its ionic radius would generally be smaller than its atomic radius.
Overall, the comparison depends on whether the nonmetal is forming an anion or losing electrons, but typically, nonmetals form anions, making the ionic radius generally greater than the atomic radius in these cases.