## 4s and 3d

Hellen Truong 2J
Posts: 50
Joined: Sat Jul 22, 2017 3:00 am
Been upvoted: 1 time

### 4s and 3d

Why are electrons removed from the 4s orbital first if it is a lower energy and is filled before the 3d orbital is?

Lena Nguyen 2H
Posts: 51
Joined: Fri Sep 29, 2017 7:06 am
Been upvoted: 1 time

### Re: 4s and 3d

4s is only lower than 3d when 3d doesn't have electrons. Once electrons enter the 3d orbitals, 3d is lower in energy than 4s. So an electron would be removed from 4s before 3d.

Posts: 20
Joined: Fri Sep 29, 2017 7:04 am

### Re: 4s and 3d

I found this concept to be quite confusing at first as well. If we are taught that 4s fills up before 3d, then why, in the case of transition metals, do the cations formed always lose the 4s electrons before they lose the 3d electrons? I've considered this concept at length and have found this very helpful article to shed some light on the subject. It makes a unique distinction between how 3d and 4s are filled, which is an explanation that seems to have support from what we know about the way electrons can move up or down between electron orbitals: one piece of information that confirms this is that we understand electrons must pass through all of the higher energy levels (until n = $\infty$) before leaving the atom. I hope you enjoy!