Electron Configuration Exceptions

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Ramneet Sandhu 3D
Posts: 50
Joined: Fri Aug 30, 2019 12:16 am

Electron Configuration Exceptions

Postby Ramneet Sandhu 3D » Sat Oct 26, 2019 12:55 pm

Could someone please explain how Chromium and Copper are exceptions to the general rules of electron configuration? Thanks!

Anne Tsai 1F
Posts: 50
Joined: Thu Jul 25, 2019 12:15 am

Re: Electron Configuration Exceptions

Postby Anne Tsai 1F » Sat Oct 26, 2019 1:02 pm

In the d subshell, having a full (d^10) or half full (d^5) subshell is more stable, so for chromium, instead of the electron configuration being [Ar]3d^4 4s^2, one electron in the p subshell rises to the d subshell, making the electron configuration [Ar]3d^5 4s^1. The same goes for copper, but instead, the electron in the p subshell rises to the d subshell and fills it completely, so the electron configuration is [Ar] 3d^10 4s^1.

Matthew Chan 1B
Posts: 111
Joined: Sat Sep 07, 2019 12:16 am

Re: Electron Configuration Exceptions

Postby Matthew Chan 1B » Sat Oct 26, 2019 3:30 pm

Chromium: [Ar]3d54s1
Takes the electron from the 4s subshell and adds it to the 3d subshell because 3d will be more stable with that fifth electron, since it will now be half filled.
Copper: [Ar]3d104s1
Takes the electron from the 4s subshell and adds it to the 3d subshell because 3d will be more stable, since the 3d subshell will now be completely filled.

In short, whenever there is a chance for the d subshell to become either half filled or fully filled or become "symmetrical" as I like to think of it, it will take the electron from the s subshell in order to achieve this more stable form.

I've attached an image in this URL that shows what I'm talking about. Hope this helps!
https://ask.learncbse.in/uploads/db3785/original/2X/7/7113372b4ca50ce5ec8be052c7aea8a0f18bd67b.png


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