## 6th Edition, Question 3.5

joanneyseung22
Posts: 31
Joined: Fri Sep 28, 2018 12:15 am

### 6th Edition, Question 3.5

So in this question, we are asked to find the electron configuration for Cu+. I originally thought that the answer was [Ar]4s^2,3d^8, but I found that the answer was [Ar]3d^10. Another post's reply stated that "2 electrons from the 4s shell move to the 3d shell in order to make the answer." Can anyone explain why this is necessary for this certain element/question?

Lauren Huang 1H
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

### Re: 6th Edition, Question 3.5

Chromium and copper are the two main exceptions to electron configuration. For both elements, an electron from 4s subshell is moved to 3d subshell to make a half full 3d (3d^5) for chromium and a full 3d (3d^10) for Copper, since doing so makes the atom more stable. So for this problem, Cu at ground state would be [Ar]4s^1,3d^10, and to make it Cu+, the electron from 4s^1 is removed because it is lower in energy than 3d^10, leaving Cu+ with the electron configuration of [Ar]3d^10

tierra parker 1J
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

### Re: 6th Edition, Question 3.5

copper has the electron configuration [Ar] 3d10 4s1 because it is more stable to have a full d shell than a partially full d shell and a full s shell. also since the 4s shell has more energy you take the electrons from that shell first so you're left with Cu 2+ as [Ar] 3d10

Ashley P 4I
Posts: 64
Joined: Wed Nov 15, 2017 3:04 am

### Re: 6th Edition, Question 3.5

I personally just remember that 3d goes before 4p and just subtract or add the one in the outer shell. I don't know if that the proper way, but I seem to get it right each time.