TBR G.C., CH. 2, passage XI, Q74

[Pose]

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Hi,

The question asks for the quantum numbers associated with Nickel dication.

I started by writing out the electron configuration, which I wrote as [Ar]4s2 3d6. I was wrong. The answer states that the electron configuration is ...3p6 3d8.

Why does the 3d shell fill before the 4s?

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[Shjanzey]

Hi,

The question asks for the quantum numbers associated with Nickel dication.

I started by writing out the electron configuration, which I wrote as [Ar]4s2 3d6. I was wrong. The answer states that the electron configuration is ...3p6 3d8.

Why does the 3d shell fill before the 4s?

Sent from my Nexus S 4G using SDN Mobile

Remember this is a Nickel dication -> Ni^2+ Therefore you need to remove two electrons from the configuration (You seem to have done this, but incorrectly). When losing electrons the Nickel atom will drop the 4s electrons first, so the electrons in the d orbital will be untouched. This is one of those weird energetic rules that pop up when you are dealing with the d shells.

So [Ar]4s2 3d8 (of a regular Nickel atom) drops two electrons to become [Ar] 3d8.

I think this is because the 4s shell is still technically farther out than the 3d shell, yet when they are adding electrons this one gets filled first. A totally weird rule that for me is best left memorized 😛

 

[FedExpress85]

It's because the first row of transition metals is in the 4th row of the periodic table. However, when you look at quantum numbers, when n=3, l can equal 0(s), 1(p) or 2 (d). Thus, the third energy level has s,p and d subshells. But your way works too.