Subshell Exceptions

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Ashley Kao 1H
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Joined: Thu Jul 25, 2019 12:16 am

Subshell Exceptions

Postby Ashley Kao 1H » Sun Oct 20, 2019 4:08 pm

During lecture on Friday, we went over exceptions for the order of subshells for Chromium and Copper. What reason is behind the formation of the subshells? Is it for the purpose of making each of the subshells more stable?

Kim Chen
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Joined: Thu Oct 10, 2019 12:15 am

Re: Subshell Exceptions

Postby Kim Chen » Sun Oct 20, 2019 4:10 pm

Yes, electrons will always act in a way that yields the most stability possible. Drawing out the version you would expect one of them to have vs. the actual version will help you conceptualize more!

Aman Sankineni 2L
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Joined: Fri Aug 30, 2019 12:17 am

Re: Subshell Exceptions

Postby Aman Sankineni 2L » Sun Oct 20, 2019 4:16 pm

"Exceptions are based on the fact that half-full or full shells or subshells are more stable than partially filled ones. When the difference in energy levels between two subshells is small, an electron may transfer to the higher level shell to fill or half-fill it. The electron occupies the higher energy level shell in violation of the Aufbau principle because the atom is more stable that way."

https://sciencing.com/what-is-the-basis ... 10232.html

This source explains the reasoning well.

Eesha Sohail 1D
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Joined: Sat Aug 17, 2019 12:16 am

Re: Subshell Exceptions

Postby Eesha Sohail 1D » Sun Oct 20, 2019 8:29 pm

For chromium, the electron configuration would have looked like the following if it followed "normal" conventions: [Ar]4s23d4
And for copper: [Ar]4s23d9
However, the atom finds more stability when the d-subshells are half-filled or fully filled:
Cr: [Ar]4s13d5
Cu: [Ar]4s13d10

The rest of the elements in those columns work much the same way.

DesireBrown1J
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Joined: Wed Sep 18, 2019 12:18 am

Re: Subshell Exceptions

Postby DesireBrown1J » Sun Oct 20, 2019 10:48 pm

In one of the UA sessions that I went to today, the UA told us to write Cr as [Ar]3d54s1 instead of [Ar]4s13d5. I do not know why he said that but can someone better explain this to me?

Ruth Glauber 1C
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Joined: Wed Sep 18, 2019 12:20 am

Re: Subshell Exceptions

Postby Ruth Glauber 1C » Fri Oct 25, 2019 12:31 pm

I think that it depends on the conditions at which the most stability is achieved.

Noah Canio 3C
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Joined: Wed Sep 18, 2019 12:20 am

Re: Subshell Exceptions

Postby Noah Canio 3C » Sun Oct 27, 2019 4:23 pm

DesireBrown3K wrote:In one of the UA sessions that I went to today, the UA told us to write Cr as [Ar]3d54s1 instead of [Ar]4s13d5. I do not know why he said that but can someone better explain this to me?


As the 3d orbital gains more electrons, it ends up having less energy than the 4s orbital. Since we're supposed to write electron configurations in such a way that we go from lower to higher energy levels, 3d is displayed before 4s.


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