## 2A. 5

Isaac Wen
Posts: 58
Joined: Wed Sep 30, 2020 9:35 pm
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### 2A. 5

Hi!

Can someone explain why the electron configuration for Cu+ is [Ar]3d^10 instead of [Ar]3d^84s^2 and why for Ga3+ it's [Ar]3d^10 instead of [Ar]3d^84s^2? Thanks!

Quinton Sprague 1A
Posts: 108
Joined: Wed Sep 30, 2020 9:35 pm

### Re: 2A. 5

Wondering the same thing... also, will we be required to know various exceptions as such on the upcoming midterm? Is there a way to figure the configuration simply given the periodic table or rather are these cemented rules for the elements?

Samantha Pedersen 2K
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### Re: 2A. 5

Remember that copper is one of the exceptions that doesn't follow the typical pattern for electron configurations, so the electron configuration for Cu (not the ion form) is [Ar]3d^10 4s^1. The 4s subshell is higher energy than the 3d subshell in this case, and electrons are always removed from the outermost subshell, so if we remove one electron from the outermost shell for Cu+ then we get [Ar]3d^10.

The electron configuration for Ga (not the ion form) is [Ar]3d^10 4s^2 4p^1. The 4p and 4s subshells are higher in energy than the 3d subshell, and again we remove the electrons from the outermost subshells, so if we remove three electrons from the outermost shell for Ga3+ then we get [Ar]3d^10.

I hope this helps!