3d and 4s subshell

[Lara Almeida 3D]

How do we know which sub-shell we are supposed to fill up first 3d or 4s?

I though we were suppose to fill 3d sub-shell up to 10 electrons before moving on to the next one (4s). But the electron configuration of Vanadium is [Ar] 3d3 4s2 and the electron configuration of Cobalt is [Ar] 3d7 4s2.

So the electron configuration for elements in the 4th period of the periodic table will have the 4s2 sub-shell complete before 3d begins to be filled?

[Ben Zhang 2H]

Yeah the 4s orbital will be filled before the 3d orbital. A helpful thing to look at for this is the periodic table. If you read it from left to right, it will tell you the order that the orbitals get filled above. For example, in the 4th row, the s comes before the d so that tells us that the 4s is filled then the 3d. It's important to remember for the the periodic table that the n level of the d in the periodic table is the row number-1.

[Naomi Christian 1E]

The 4s subshell is filled before the 3d subshell because without any electrons, the 3d subshell has more enrgy than the 4s subshell. However, once electrons start to fill the 3d subshell, it will have less energy than the 4s subshell and will thus be listed before the 4s. It just has to do with how much energy each subshell has.

[Muryam_Hasan_2I]

It's shown a lot better on the periodic table, with the 4s subshell coming before 3d going from left to right; however, once 3d gains electrons, it has less energy and therefore switches in order with 4s. So the order of elemental configurations would go 4s, 4s^2, 3d4s^2, and so on. Your last question is correct: the 4s subshell will be filled before starting to fill 3d, but the 4s subshell will only be incompletely filled from then in the exceptions of 3d^4 or 3d^9 (in which case one electron will move from 4s to 3d to fill or half fill this subshell).

[madelyn kelly 1I]

The 4s orbital gets filled up before 3d because 4s is lower in energy than 3d. The levels with the lower energy levels are filled first according to the Aufbau principle.

[Sarah Hong 2K]

You always fill up the 4s orbital before the 3d orbital because 4s has lower energy than 3d. But when writing out the electron configuration, you must write 3d before 4s.

[Acharya Ranawat 3E]

You originally fill up the 4s subshell since when there aren't any electrons in the subshell, 4s is actually considered a lower state. However, once electrons fill in the 4s subshell, the 3d is actually considered the lower state. Hence, the 3d shell then fills up. Hope this helps!

[Ishpreet Kaur 3C]

You fill the 4s subshell first, but from scandium onwards, 3d is written before 4s and is filled.

[Clarence Clavite 2K]

The 4s subshell will always be filled in first because it has a lower energy level when it isn't filled. When it is filled it actually has a higher energy level than 3d which is why we write it as 3d^1 4s^2 when we do electron configurations. Hope this helps!

[Hope Galarneau 1A]

The 4s subshell would be filled up first. The only reason that 3d appears before 4s in the electron configuration is because once electrons start to fill the d subshell, it has a lower energy than the 4s subshell. Typically, you fill the subshells according to their location on the periodic table, but when writing them in the electron configuration you would list them in numerical order because it will show the order of energies.

[Sonia Virk 2A]

The 4s subshell comes before the 3d in terms of number of electrons but it is written with 3d before 4s because electron configuration is typically written in order of the principle quantum number (n).

[Molly McAndrew 1 1H]

Do we always have to list the 3d subshell before the 4s subshell when writing out electron configuration? It seems that when we usually always list the s subshell first, before the p and d, but is 3d specifically different?

[Alexandra Gill]

4s fills up before 3d because 4s has lower energy than 3d. There are two exceptions though for Copper and Chromium. Cr= [Ar]3d^54s^1 and Cu=[Ar]3d^104s^1 because the half and full d subshell has lower energy than the 4s.

[Alexis Rempillo 3B]

So what happens is that when we move to the fourth period we fill out 4s first, and we would have 4s2 across the table except for chromium : [Ar]3d5 4s1 and copper: [Ar]3d10 4s1. We fill out 4s first (besides those two elements) because 4s is a lower energy state than 3d. And I assume that these rules would follow in the next periods. Copper and chromium are exceptions because it is at that state where it is stable.

[405532435]

4s fills up before 3d! i know this was confusing because it has been seen written in multiple ways, but the correct way is 4s first. Hope this helps!

[sidneypalacios]

Based on the Aufbau Principle, the energy levels lower in energy get filled up first; therefore, 4s will fill up before 3d.

[Arpita Padhy 3E]

It took me forever to understand this, but 4s is supposed to fill up before 3d.

[Lindsey Walter 3E]

We fill the 4s orbital before we fill the 3d orbital. This is because the 4s orbital is lower in energy than the 3d orbital, and according to the Aufbau principle, we fill up lower energy orbitals before ones of higher energy. The periodic table is great at demonstrating this, you just follow the table in order and it will correspond to the orbital you fill as you add electrons.