Electron configuration 4s and 3d

[Melody Haratian 2J]

Hi everyone!
Just to clarify, is the 4s higher than energy than the 3d orbital? It’s energy was mentioned in lecture a couple of times, but I’m a little confused.
Thanks

[John Pham 3L]

I think the energy depends on whether or not the 3d orbitals have electrons in them.

When there are no electrons occupied in the 3d orbitals, then 4s has lower energy than 3d.
When there are electrons in the 3d orbitals, then 4s has higher energy than 3d.
After Ca, the 4s shell has higher energy than 3d.

[Arezo Ahmadi 3J]

Hi, you can look at it in terms of the shells. The 4th shell should have a higher energy than the 3rd shell, and this energy increases as the shell number increases. This is why when we write electron configurations, we need to write 3d before 4s, because electron configurations need to be written so that the shells are in order of increasing energy.

I hope this helps!