## 2A.5

Ryan Chang 1C
Posts: 105
Joined: Sat Aug 24, 2019 12:17 am

### 2A.5

Give the ground-state electron configuration expected for each of the following ions: (a) Cu 1+ ; (b) Bi 3+ ; (c) Ga 3+ ; (d) Tl 3+

For part A, I thought that the answer was [Ar]3d^84s^2 but the solution manual says that the answer is [Ar]3d^10. Why are the electrons from the 4s orbital put into the 3d orbital?

WesleyWu_1C
Posts: 117
Joined: Thu Jul 25, 2019 12:16 am

### Re: 2A.5

If you remember in class, Cu is an exception for telling the electron configuration from the periodic table. From reading the periodic table, we would expect the configuration to be [Ar]3d^9 4s^2, BUT through experiments, scientists have found that the e- configuration is actually [Ar]3d^10 4s^1 because copper would have lower energy at this electron configuration with a filled d subshell. That's why for Cu+, the new e- configuration would be [Ar]3d^10

Leyna Dang 2H
Posts: 104
Joined: Thu Jul 25, 2019 12:17 am

### Re: 2A.5

I had problems with this at first too, but I think it has to do with the element being ionized. You're supposed to fill the d block first so that it's more stable(?), and you do this by taking the 2 electrons from the 4s orbital and moving them to the 3d orbital. This now makes the configuration for Ga3+ = [Ar]3d^10.

Ryan Chang 1C
Posts: 105
Joined: Sat Aug 24, 2019 12:17 am

### Re: 2A.5

WesleyWu_3C wrote:If you remember in class, Cu is an exception for telling the electron configuration from the periodic table. From reading the periodic table, we would expect the configuration to be [Ar]3d^9 4s^2, BUT through experiments, scientists have found that the e- configuration is actually [Ar]3d^10 4s^1 because copper would have lower energy at this electron configuration with a filled d subshell. That's why for Cu+, the new e- configuration would be [Ar]3d^10

This also happens for part D of the question. Why does the same thing happen to Tl 3+if Tl is not listed as one of the exception elements?