Order of subshells

[Melinda Luo 2G]

Is it that important that we put the d subshells first then the s subshells? In the past, I was told that it doesn't really matter although the convention was to put the s subshell first then the d subshell (for example, 4s²3d¹) since the valence shell should be written on the outside. While I understand Dr. Lavelle's reasoning for writing it the other way, is it that crucial that we follow his way?

[Vivek Chotai 2C]

I think we should write the 3d orbital before the 4s orbital because we want to make sure we stay consistent with the order of energy. Since an electron in the 4s orbital has greater energy than an electron in a 3d orbital, we should write 3d first and then 4s

[Charlotte McDonough 2B]

I agree, in the past I wrote electron configurations with the valence orbitals first. However, because Lavelle has emphasized the conceptual reasons why we write the d subshell first in his class, I would follow this convention for his tests/homework.

[raynebunado]

I've been told also that it doesn't matter, but I would recommend following the method Dr. Lavelle uses! So in this case I'd do 3d^1 4s^2

[SarahOMalley1D]

Hi! Just to add to some previous answers, when two electrons have filled our s subshell, we should order our d subshell before our s subshells. We do this because the s state is higher energy than the d state when two electrons are filling the s state. However, there are exceptions to this statement. Chromium and copper both have unfilled 4s subshells, but we still place their 3d subshells before 4s in their electron configurations. This is because having a half-filled d subshell (Cr) or a full d subshell (Cu) are both lower energy level states than having a full 4s subshell and partially full 3d subshell.

[Hailey Sarmiento 3E]

I believe the only time you put the d orbitals first in electron configuration is when they have a lower energy level than the s orbital electrons. For instance, the professor explained the 2 exceptions that are important to know. These were for the half full d shells and the full d shells (d5 and d10). When a d shell is half or full, the d orbital comes first like in Chromium (Cr): [Ar] 3d5 4s1

[SuryaDham 3E]

since a 3d orbital has lower energy than a 4s orbital, you should put the 3d orbital before the 4s.

[Grant_2A]

I agree with what everyone is saying, Lavelle emphasized writing it in order of energy in lecture so I would put the d before the S.