The atomic radius is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined.

Atomic Raddi

Metals elements lose valence electrons to form cation ions. Cation radii (IR) are always smaller than atomic radii (AR) [i.e. IR < AR]

Non-metal elements gain valence electrons to form anion ions. Anion radii (IR) are always larger than atomic radii (AR) [i.e. IR > AR]