## Order of electron configuration

Amy Luu 2G
Posts: 105
Joined: Wed Sep 18, 2019 12:19 am

### Order of electron configuration

Hello! I'm confused on how to correctly write electron configurations. For example, in the homework problem 1E.23, it asks for the electron configuration of Ga, Ge, As, Se and Br. For Ga, I wrote the electron configuration as [Ar] 4s23d104p1. However, in the solution manual, they wrote it as [Ar]3d104s24p1. Is there a specific order or can I write the electron configuration how I did.

Ellis Song 4I
Posts: 102
Joined: Thu Jul 11, 2019 12:17 am

### Re: Order of electron configuration

3d should come before 4s for atoms with an atomic number after 20

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

### Re: Order of electron configuration

The 3d orbital has a slightly lower energy level than the 4s orbital, which is why 3d comes before 4s. The 3d orbital is filled up with electrons first, then the 4s orbital, then the 4p orbital.

alexfwang3g
Posts: 50
Joined: Thu Jul 11, 2019 12:16 am

### Re: Order of electron configuration

3d comes before 4s due to its lower energy state.

SarahCoufal_1k
Posts: 102
Joined: Thu Jul 25, 2019 12:17 am

### Re: Order of electron configuration

After Atomic number 20 (i.e. 20 electrons) 3d has a slightly lower energy level and you want to fill them from low to high. So do 3d and then 4s

claribel charway 1I
Posts: 55
Joined: Wed Sep 11, 2019 12:15 am

### Re: Order of electron configuration

Although 4s is filled first, you write 3D first because it still occupies a slighter lower energy level.

Kylie Lim 4G
Posts: 110
Joined: Sat Aug 17, 2019 12:15 am

### Re: Order of electron configuration

3d is at a lower energy state than than 4s so it is written first, even though the d block comes after the s block in the periodic table.