# What happens to ionic size down a group?

May 14, 2018

Would it not become larger....?

#### Explanation:

Cations INVARIABLY become smaller upon ionization with respect to their parent atoms upon ionization.

$M \left(g\right) + \Delta \rightarrow {\underbrace{M {\left(g\right)}^{+}}}_{\text{smaller cation}} + {e}^{-}$

Why? Because invariably our definition of ATOMIC RADIUS is the radius of the VALENCE electron...and this is necessarily removed upon oxidation.

On the other hand...elements from the right hand side of the Periodic Table (as we face the Table), tend to be smaller in radius. But when these atoms are reduced, they add an electron to the valence shell, and given constant $Z$, the electronic radius is NECESSARILY INCREASED upon reduction.

But the question asks what happens down a Group...a column of the Periodic Table. Because of the inner electronic shells, atomic size should INCREASE, and cationic/anionic radii should increase proportionally.

As chemists, as physical scientists, we should interrogate what data exist...

Do these data support or counter the argument made above? (The data are listed in picometres, $1 \times {10}^{-} 12 \cdot m$.) Why or why not?