3d before 4s

[victoria1l]

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]

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

[Jimmy lira-1G]

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]

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

[Elena 1H]

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

[Natalie_Martinez_1I]

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]

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]

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]

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]

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!