Electron Configuration of Gallium

[Nancy Le - 1F]

According to the periodic table, the electron configuration of Ga is [Ar]4s^2 3d^10 4p^1. However, why did Dr. Lavelle write it as [Ar]3d^10 4s^2 4p^1 in class?

[Deborah Cheng 1F]

My TA explained that even though it is listed that way in the periodic table, 3d has lower energy when 4s is filled. Dr. Lavelle wants us to list them in order of energy level, so the correct electron configuration for Gallium would be [Ar]3d^10 4s^2 4p^1

[Michaela Capps 1l]

Yes, even though you fill the 4s before the 3d orbital, you should write it in order of ascending energy, which would be 3d then 4s. This also makes it easier to see what electrons will be ionized (from the highest energy orbital)

[Matthew Lee 3L]

I concur with the previous answers. The reason you put the 3d first is because it has the lowest energy. This also makes it easier when creating cations to know which electrons you would remove first.