Why Does the Ni+ Ion Have an Electron Configuration of [Ar]3d9?

[thonwer]

Homework Statement

Which is the electron configuration of the Ni⁺ ion?

Homework Equations

Ni : [Ar]4s²3d⁸

The Attempt at a Solution

Ni⁺: [Ar]4s¹3d⁸

Apparently this solution is wrong and should be Ni⁺: [Ar]3d⁹ but I do not know why. As far as I know 4s has less energy than 3d so, why does one electron promote from 4s to 3d after one ionization?

 

[PietKuip]

This kind of thing is subtle. The only way to solve this kind of problems is by quantum-mechanical calculations, for example Cowan's old code.

In hydrogen, all orbitals with the same principle quantum number have (almost) the same energy. But when there are more electrons, the "circular" 3d orbitals are shielded much more than s-electrons, which makes that 4s is filled before 3d in transition metal atoms.

In heavier atoms, the 3d binding energies are larger than 4s, 4p, 4d, 4f.