## 3d before 4s

victoria1l
Posts: 29
Joined: Fri Apr 06, 2018 11:05 am

### 3d before 4s

Is it correct to say that as soon as the 3d orbital has at least one electron you write it before the 4s orbital except for Cr and Cu?

Jasmine Emtage-1J
Posts: 24
Joined: Fri Apr 06, 2018 11:02 am

### Re: 3d before 4s

Yes, that's correct because the 3d orbital is higher in energy than the 4s orbital.

Jimmy lira-1G
Posts: 61
Joined: Fri Apr 06, 2018 11:03 am

### Re: 3d before 4s

Your question is unclear, but I do believe your statement is true , and the only exceptions are Cr and Cu, as I remember him saying that in lecture ;hope this helps

https://chem.libretexts.org/Core/Physic ... s_Orbitals

Jimmy Lira 1G

Kalsuda Lapborisuth 1B
Posts: 27
Joined: Fri Apr 06, 2018 11:03 am

### Re: 3d before 4s

Is it also correct to say the same for 5s and 4d?

Elena 1H
Posts: 27
Joined: Fri Apr 06, 2018 11:04 am
Been upvoted: 1 time

### Re: 3d before 4s

^Yes because 4d is at a lower energy level than 5s

Natalie_Martinez_1I
Posts: 30
Joined: Mon Feb 26, 2018 3:00 am

### Re: 3d before 4s

I'm confused by a previous reply that says that says that 3d is higher in energy that the 4s orbital. I thought it was the other way around?

Alma Flores 1D
Posts: 64
Joined: Wed Nov 08, 2017 3:01 am

### Re: 3d before 4s

The 4s orbital has higher energy then the 3d orbital. After the 4s is completely filled, 3d is lower in energy than 4s.

105012653 1F
Posts: 30
Joined: Fri Apr 06, 2018 11:02 am

### Re: 3d before 4s

Alma Flores 1D wrote:The 4s orbital has higher energy then the 3d orbital. After the 4s is completely filled, 3d is lower in energy than 4s.

Although I know this to be true, is there an explanation as to why 3d is lower in energy than 4s only after the 4s is completely filled?

breannasung_1K
Posts: 30
Joined: Fri Apr 06, 2018 11:05 am

### Re: 3d before 4s

the 4s orbital is lower in energy, and therefore electrons fill the 4s orbital first before 3d. However, when you are writing the electron configuration, it is conventional to write 3d before 4s.

Haison Nguyen 1I
Posts: 30
Joined: Fri Apr 06, 2018 11:04 am

### Re: 3d before 4s

When there are no electrons, 4s is lower in energy than 3d, but once 4s is filled, 3d becomes lower in energy. At least that is what I think happens, please correct me if I'm wrong!