energy in electron configurations

[Kaylee Nezwek 1D]

Hi! In the 10/26 lecture I thought Dr. Lavelle said we write electron configurations in order of lower to higher energy. However, I got confused when we learned that after the 4s orbital, the 3d state is written first, because I wrote in my notes that 4s was lower in energy than 3d. Is 4s actually higher in energy than 3d? (I may have just mixed them up because I also wrote that 3d goes first since it is based on energy, and we put lowest last, but I just wanted to clear this up)

[Kayla Law 2D]

Hi! I believe that 4s is more stable (and therefore has a lower energy) than 3d for Potassium and Calcium, but that once you get to the d-block elements, the energy of the 3d orbitals become slightly less than that of the 4s orbital. Hope this helps! :)

[annabelchen2a]

Hey! So I noticed you said "I also wrote that 3d goes first since it is based on energy, and we put lowest last" but I just wanted to remind you that when we write electron configurations we assign electrons to the lowest energy orbitals first, and then successively add them to higher energy orbitals until we run out of electrons. So that means the lowest energy sublevel is always going to be the 1s sublevel (in other words, we put highest [energy] last).

[Claire_Latendresse_1E]

We write electron configurations from the lowest energy to highest energy, and because 3d is lower in energy than 4s, we would write it first :)

[EmilyGillen_1A]

When you are writing electron configurations, as electrons start to use the "d" orbitals the atom deals with more energy they begin to experience more stability when the 4s comes before the 3d. It sounds like you understand the concept but are just a little confused, but once you get up to the 3d/4s just remember that the 3d actually has higher energy potential and will therefore get filled after the 4s, which has less energy.

[Pranav Daggubati 3C]

There are two conventions for writing electron configurations, the one where the pattern on the periodic table is visible and the one where the energy level difference is visible. For example, putting 4s before 3d shows the former pattern while putting 3d before 4s shows the latter.

[Margaret Xu 3C]

Hi Kaylee! I read that whenever you have the opportunity to complete a half d-shell or a full d-shell (going from 4 electrons to 5 or 9 electrons to 10), then you take 1 electron away from the s-shell and put it into the d-shell. I believe this is because a half or full d-shell is more stable and requires less energy.

For example, the electron configuration of Ag is [Kr]4d¹⁰5s¹ instead of [Kr]5s²4d⁹. Please correct me if I'm wrong!

[Katie Lam 2J]

Hey Kaylee! I think we will always have to write 3d before 4s. However, if there are 9 electrons in 3d, and 2 electrons in 4s, then we can move the one electron from 4s to 3d. Having a 3d shell with only 9 electrons is very unstable, so adding that one electron to make a full shell will make it more stable. This is applies to the electron configuration of copper, and copper was one of the exceptions to the typical electron configuration!