Exceptions to the rules

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Alfred Barrion 2H
Posts: 100
Joined: Sat Jul 20, 2019 12:16 am

Exceptions to the rules

Postby Alfred Barrion 2H » Sun Oct 20, 2019 10:37 pm

Why does Cr and Cu not follow the rules for electron configuration? Why isn't the s block completely filled?

chemboi
Posts: 101
Joined: Sat Jul 20, 2019 12:16 am

Re: Exceptions to the rules

Postby chemboi » Sun Oct 20, 2019 10:49 pm

In the cases of these atoms, a lower energy configuration is for each of the five 3d orbitals to be half-filled (Cr) or filled (Cu) and the 4s to have 1 electron rather than 2. I believe these energy level differences are quite small, so it is difficult to have an intuition for these exceptions beyond knowing which elements they are.

gferg21
Posts: 51
Joined: Sat Aug 17, 2019 12:17 am

Re: Exceptions to the rules

Postby gferg21 » Sun Oct 20, 2019 10:51 pm

The atoms of Cu and Cr are the most stable when they half of their shell can be filled, meaning that if the atoms did not receive that extra electron they would essentially be volatile, which is bad for an atom. The s-block is already filled in the periods 1-3, and therefore the s-orbital is fairly stable already. Because the 3-d orbital is the first of the d-orbitals to be filled, the d shell is more unstable, so adding the electron from the s-block makes it more stable. Hopefully this helps.

Alexa Mugol 3I
Posts: 54
Joined: Sat Aug 17, 2019 12:17 am

Re: Exceptions to the rules

Postby Alexa Mugol 3I » Sun Oct 20, 2019 11:02 pm

The electron configuration is most stable this way because it minimizes the electron-electron repulsion. Therefore, the electrons are more stable in 3d54s1 than in 3d44s2 since they're all unpaired.


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