## Exceptions in electronic configurations?

EvaLi_3J
Posts: 53
Joined: Wed Oct 02, 2019 12:16 am

### Exceptions in electronic configurations?

Does anyone know which atoms are the exceptions for electronic configuation?
And why are they exceptions?

Posts: 45
Joined: Fri Aug 30, 2019 12:18 am

### Re: Exceptions in electronic configurations?

The exceptions to electron configurations are Chromium and Copper. Basically, in these two elements, you do not fill up the 4s shell first. Instead, you put one electron into the 4s shell and then move on to the 3d shell. So Cr's electron configuration is [Ar] 3d5 4s1 and Cu is [Ar] 3d10 4s1. The way I like to think about it is in a visual way. When you draw out the electron configuration, it is more symmetrical when each orbital in the d subshell is half-filled/ completely filled. In terms of scientific explanation as to why this is, it is a mathematical proof that we don't really need to know. My TA told me not to think about the explanation too much and said this configuration is just "more favorable."

EvaLi_3J
Posts: 53
Joined: Wed Oct 02, 2019 12:16 am

### Re: Exceptions in electronic configurations?

HanaAwad_4B wrote:The exceptions to electron configurations are Chromium and Copper. Basically, in these two elements, you do not fill up the 4s shell first. Instead, you put one electron into the 4s shell and then move on to the 3d shell. So Cr's electron configuration is [Ar] 3d5 4s1 and Cu is [Ar] 3d10 4s1. The way I like to think about it is in a visual way. When you draw out the electron configuration, it is more symmetrical when each orbital in the d subshell is half-filled/ completely filled. In terms of scientific explanation as to why this is, it is a mathematical proof that we don't really need to know. My TA told me not to think about the explanation too much and said this configuration is just "more favorable."

Thank you so much!!

ZevMarx-Kahn3C
Posts: 52
Joined: Sat Aug 17, 2019 12:17 am

### Re: Exceptions in electronic configurations?

Are these the only exceptions we need to know?