electron configurations

[Isela Tamayo 3H]

Why is it that a 4s orbital comes before a 3d orbital when I write the electron configuration? I thought that it went in order.

[Sammy Liu]

Why is it that a 4s orbital comes before a 3d orbital when I write the electron configuration? I thought that it went in order.

Lavelle actually writes the 3d orbital before the 4s orbital, but everybody else does it the other way around. This is probably because the 4s orbital requires less energy to be filled up, so it is fulled up before the 3d orbital.

Hope this helps!

[Cassidy Chiong 2J]

In lecture, we discussed how, when the 4s subshell has electrons while the 3d subshell is still empty, then the 4s subshell is lower in energy than the 3d subshell. However, once the 4s subshell has electrons and electrons begin the enter the 3d subshell, then the 3d subshell has a lower energy than the 4s subshell. That is why we typically write 3d before 4s in electron configuration.

[Stephanie Trinh 1F]

From what I understand, when the 3d orbital is being filled out after the 4s orbital is already filled, the 3d orbital ends up with less energy than the 4s orbital and that is why it is written first. Otherwise, without the electrons in 3d, the 4s orbital is still lower.

[Sonia Virk 2A]

It is written with 3d before 4s because electron configuration is typically written in order of the principle quantum number (n).