4s and 3d

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Isaac Wen
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4s and 3d

Postby Isaac Wen » Mon Nov 02, 2020 11:56 am

Hi!

Can someone explain why 4s is sometimes written before 3d and why after Z=20, it's written after 3d?

Seraphina Joseph 1C
Posts: 97
Joined: Wed Sep 30, 2020 9:31 pm

Re: 4s and 3d

Postby Seraphina Joseph 1C » Mon Nov 02, 2020 12:05 pm

I have in my notes that after 4s state/orbital is occupied and electrons enter the 3d state, then the 3d state is lower in energy than 4s, but for multi electron atoms after atomic number(z) 20 4s is in a higher state of energy than 3d. The atomic number(z) 20 is for Ca, which is when the 4s orbital is occupied. Period 5 has the same trend, where the 4d state is lower in energy than the 5s stats after 2 electrons have occupied the 5s state.
I hope this helps!

905290504
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Re: 4s and 3d

Postby 905290504 » Mon Nov 02, 2020 3:03 pm

4s is a lower energy orbital than 3d and you want to have the lowest energy configuration possible, so you want to fill up the 4s shell before the 3d. There are two (i think) exceptions which the textbook covers, so i'd check that out!

Isaac Wen
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Re: 4s and 3d

Postby Isaac Wen » Fri Nov 06, 2020 12:56 am

Awesome thanks! And these are all based on experimental findings right?

Jaden Ji 2K
Posts: 50
Joined: Wed Sep 30, 2020 9:54 pm

Re: 4s and 3d

Postby Jaden Ji 2K » Fri Nov 06, 2020 1:11 am

In the lecture of 10/26 Dr. Lavelle says that you can figure it out based on the periodic table and by calculating the numbers using Pauli's Exclusion Principle and Hund's rule. I think it should be fine if you just remember that the 4s goes before the 3d.


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