Number of Unpaired Electrons

[Nicole Jakiel 4F]

Can anyone explain why Ni^2+ has two unpaired electrons? I understand how to get its ground state electron configuration, [Ar]3d^8, but I don't understand why it has two unpaired electrons (instead of zero unpaired electrons).

[Francis_Nguyen3D]

Hello,
when you do the electron configuration diagram for 3d^8 three orbitals would be filled out of the five orbitals available. Two orbitals would have only one electron in them-making them unpaired.
https://www.adichemistry.com/jee/qb/coordination-chemistry/1/q1-3.png

[monikac4k]

The key to this is following Hund's Rule for electron configurations.
We know there are 8 electrons on the 3d subshell.
We also know there are 5 orbitals in the d subshell (5 possible ml values; accommodates 10 electrons).
First, we can place one electron in each of the 5 orbitals. 3d: ^ ^ ^ ^ ^
Now we have 3 left over electrons that we can place in 3 of these orbitals, filling them. 3d: ^v ^v ^v ^ ^
In the end, we are left with two orbitals that have only 1 electron in them.
(Sorry if my visuals are weird and hard to grasp. I tried using ^ and v to signify the different electron spins).