# How do you compare ionic radii?

The units are in $\text{picometres} \equiv {10}^{-} 12 \cdot m$. Because atomic radii are reasonably defined by the radius of the valence, the outermost electron, and thus with RESPECT TO THE PARENT ATOM, CATIONS are SMALLER (because they have been OXIDIZED), and ANIONS ARE LARGER (cos' they have been reduced).