4s or 3d first?

[Darren Nguyen 1F]

I wrote "4s before 3d" in my notes but google says the config for Sc is [Ar] 3d¹ 4s²

[Ben 1B]

I believe we should write 3d first.

[katrinawong3d]

You fill the 4s shell before the 3d shell. But, I believe Lavelle wants us to write 3d first since you remove electrons from 4s first.

[Tiffany Dong_4e]

Lavelle wants us to write 3d before 4s, but I in general it isn't incorrect to write 4s before 3d. I think you should maintain class expectations for the test though.

[Shimei_2F]

My TA said that we should write 3d first so the shells are in chronological order.

[Anna Chen 1K]

The 4s orbitals have a lower energy than the 3d orbitals, so the 4s orbitals are filled first. However, Lavelle has said to write 3d first.

[Grecia Velasco 1G]

The 4s orbitals have a lower energy than the 3d orbitals, so the 4s orbitals are filled first. However, Lavelle has said to write 3d first.

Do you know if Cr and Cu are the exceptions to this rule because their 3d orbitals are filled first? Thank you!

[Grecia Velasco 1G]

You fill the 4s shell before the 3d shell. But, I believe Lavelle wants us to write 3d first since you remove electrons from 4s first.

So we write 3d first regardless if 4s is filled in first? Does this rule apply to any other orbitals? Because my TA said to follow the order:
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f

with the order being: 1s, 2s, 2p, 3s, 3p, 4s, 4d, 3d, 4p, 4f
But Lavelle wants us to put 3d before 4s. Does this apply to any other orbital?

[Nyari Muchaka_Discussion 4A]

On the periodic table the 4s comes before the 3d. But on the test you write it out in terms of energy subshells. So when you write your final answer 3d should be first because the 3d shell comes before the 4s shell as it is a lower energy level(go in ascending order of the numbers), it is just not displayed that way on the periodic table itself.

[Sharon Rodriguez 3H]

The 4s orbitals have a lower energy than the 3d orbitals, so the 4s orbitals are filled first. However, Lavelle has said to write 3d first.

Even though 4s is lower in energy, is this where valence electrons would reside? I was under the impression by things I have read that valence e- consisted of those with the highest energy AND in the outer shell

[pmokh14B]

The 4s shell is filled first, any energy level that is higher is always filled first. But you write it second because it has higher energy and if any electron is removed from the atom it's removed from a higher energy shell first>

[Mandeep Garcha 2H]

4s comes before the 3d on the periodic table, which is why you might want to write the electron configuration in that order. However, we have been told write it out in order of the energy of the subshells (low-high energy).

[MAC 4G]

Do you know if Cr and Cu are the exceptions to this rule because their 3d orbitals are filled first? Thank you![/quote]

Cr and Cu are are exceptions in which they don't have a full 4s shell. One of the e- is moved into the 3d shell. So Cr: [Ar]3d^5 4s^1 and Cu: [Ar]3d^10 4s^1. My TA said you will never see 3d^4 or 3d^9.

[Jasmine Vallarta 2L]

put them in order of "n"; so 3d goes before 4s

[Avnita C_4B]

we write 3d before 4s due to the location of the electrons on that orbital and how they react with losing/gaining electrons.