4s and 3d Orbitals  [ENDORSED]

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Rebecca Altshuler 1D
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Joined: Fri Sep 28, 2018 12:15 am

4s and 3d Orbitals

Postby Rebecca Altshuler 1D » Mon Oct 22, 2018 1:47 pm

I remember from lecture that the 4s orbital has more energy than the 3d orbital, but if this is the case, why is the 4s orbital filled first?

Aria Soeprono 2F
Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

Re: 4s and 3d Orbitals  [ENDORSED]

Postby Aria Soeprono 2F » Mon Oct 22, 2018 2:02 pm

According to Aufbau's principle, orbitals are filled in accordance to the lowest value of orbitals. For 4s, n+1=4+0=4, and for 3d, n+1=3+2=5
So, although 4s is higher in energy because it has a higher value of n, it is filled first because it has a lower value of orbitals.

Aria Soeprono 2F
Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

Re: 4s and 3d Orbitals

Postby Aria Soeprono 2F » Mon Oct 22, 2018 3:05 pm

I forgot to add that for multi-electron atoms that come after atomic number 20, the 4s state is higher in energy than the 3d orbital, as you would expect. The 3d orbital is lower than the 4s only on the condition that the 4s orbital is occupied.

MaggieMatern_Dis1H
Posts: 30
Joined: Fri Sep 28, 2018 12:19 am

Re: 4s and 3d Orbitals

Postby MaggieMatern_Dis1H » Mon Oct 22, 2018 5:06 pm

Image
In some cases, the 4s orbital actually has LESS energy than the 3d orbital, and thus is filled first. This occurs for K and Ca. However, when an element's atomic number is greater than 20, e.g. Scandium (Sc) the 4s orbital has MORE energy than the 3d orbital, which is expected.


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