The above animation shows the filling of the Titanium subshells. Notice that the 4s fills before the 3d. But when electrons are in both the order is reversed with the 3d having lower energy than the 4s.

When electrons are lost, to form ions, they are lost from the 4s subshell first. Look at the animation above. The Titanium ion(Ti²⁺) has the electronic configuration
1s², 2s², 2p⁶, 3s², 3p⁶, 3d² .

Exercises

Write the electronic configuration of the following ions.

Cu²⁺
Fe³⁺
Mn²⁺
Zn²⁺
Cr³⁺

Solution