Question

explain why the ionic radius of magnesium is smaller than its atomic radius

Answer 1

Explanation:

IF THE ATOM LOSES ITS OUTER ELECTRONthen it will become positive charged..THE IONIC RADIUS BECOMES SMALL AS IT LOSES ONE ELECTRON IN ENERGY SHELL

Answer 2

Explanation:

To understand this you need to keep in mind that size of atom is measured in radius from it's nucleus to the valence shell (last shell).

Magnesium as 2 electron in it's last shell and it's configuration goes like (Z= 12):

$\\\tt 1s^{2} \ 2s^{2} 2p^{6} \ 3s^{2}$

The last electrons go in 3s2 shells and when they are removed to gain a magnesium ions the last shells get's vacant and  the net size of the atom is measured only upto 2nd shell since it's the new valance shell reducing the size.

Configuration of $\\\tt Mg ^{2+}$:

$\\\tt 1s^{2} \ 2s^{2} 2p^{6}$