## Notation of electron configurations of ions

Katherine Fitzgerald 1A
Posts: 40
Joined: Fri Sep 29, 2017 7:05 am

### Notation of electron configurations of ions

In 2A3(b), we are asked to give the electron configuration for As3+. The configuration for As is normally [Ar]4s24p3. However, when As loses three electrons, the configuration is [Ar]3d104s2. I am comfortable with the idea that it loses 3 electrons from 4p3. However, I don't understand why the electron configuration is now [Ar]3d104s2 instead of just [Ar]4s2. Why include the 3d10 if you still haven't removed the 4s2 shell? Is it really valence in that case, especially when it is filled? On the flip side, why do we not write As as [Ar]3d104s24p3?

Gwynneth Orlino 1B
Posts: 26
Joined: Wed Nov 21, 2018 12:18 am

### Re: Notation of electron configurations of ions

The configuration for As is [Ar] 3d10 4s2 4p3. So As3+ would be [Ar] 3d10 4s2.

Kevin To 1B
Posts: 32
Joined: Sat Feb 02, 2019 12:15 am

### Re: Notation of electron configurations of ions

The 3d10 orbital has to be included in the electron configuration.

Yasmin Olvera 1D
Posts: 29
Joined: Thu Feb 14, 2019 12:15 am

### Re: Notation of electron configurations of ions

Since As is in the fourth period it will include 3d10 in its original configuration

somyapanchal1D
Posts: 34
Joined: Mon Jun 17, 2019 7:23 am

### Re: Notation of electron configurations of ions

The electron configuration for As is [Ar]3d104s24p3. As3+ means that 3 electrons have been removed. When you're writing the electron configuration for As3+, you remove electrons from the valence shell. In this case, you remove electrons from the 4p orbital. Thus, you get [Ar]3d104s2. You cannot just remove 3d10 from the answer because you have not removed electrons from the 3d orbital yet.

Daniel Kim 1D
Posts: 38
Joined: Wed Oct 03, 2018 12:17 am

### Re: Notation of electron configurations of ions

As is in the fourth period, therefore, 3d being a lower energy level it will be included in the electron configuration before 4s.