Why Mg2+ ion has smaller radius than Mg atom?
didn't the most outer energy level become depleted, and the net force on the electrons become stronger stronger in the absence of two outer electrons?
The Mg2+ ion has a smaller radius than the Mg atom because it loses two electrons to form the ion.
To understand why this happens, let's look at the electronic configuration of a neutral Mg atom (atomic number 12), which is 1s² 2s² 2p⁶ 3s². The outermost electron shell is the 3rd shell, and the 3s subshell contains the two valence electrons. These valence electrons are shielded by the 1s² and 2s² 2p⁶ inner electron shells.
When Mg loses two electrons to form Mg2+ ion, the electronic configuration becomes 1s² 2s² 2p⁶. The two valence electrons are removed, leaving behind a completed 2nd shell.
So, the removal of the two valence electrons reduces the electron-electron repulsion between the remaining electrons. Consequently, the effective nuclear charge experienced by the remaining electrons increases. As a result, the outermost electron cloud contracts closer to the nucleus, leading to a smaller atomic radius for the Mg2+ ion compared to the neutral Mg atom.
In summary, the removal of valence electrons causes a decrease in the atomic radius because of increased effective nuclear charge and reduced electron-electron repulsion.