## 4d^10 and 5s rule

Melissa Villanueva1K
Posts: 64
Joined: Wed Nov 15, 2017 3:01 am

### 4d^10 and 5s rule

Could someone briefly describe what the rule or what the importance was behind the 4d^10 coming before the 5s when writing out the electron configuration for a certain element? Thanks!

Becky Belisle 1A
Posts: 81
Joined: Fri Sep 28, 2018 12:18 am

### Re: 4d^10 and 5s rule

I think it's based on the energies of those sublevels. 4d has lower energy than 5s, and the electron configurations are written in order of increasing energy.

Sophia Ding 1B
Posts: 62
Joined: Fri Sep 28, 2018 12:16 am

### Re: 4d^10 and 5s rule

Going off of Becky, the rule is that the s orbital has higher energy than the d orbital when there is an electron present in the s orbital (s > d), but when there is no electron in the s orbital, it has lower energy than the d orbital (s < d). Thus in electron configurations, because you have to fill the s orbital before filling the d orbital, the s orbital will have a higher energy than the d orbital. So in terms of ionization energy, the first electrons removed from the atom would be from the s, in this case the 5s orbital, before the d orbital, thus being placed in name configuration after the d orbital to represent this.