Mad Man
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Why do I have to fill in the 3d orbitals first? This contradicts the Aufbau principle. It doesn't say anything in my textbook, just to keep in mind that they are different. I'm doing AQA chemistry A level. Should I just learn these exceptions and are there any more of these exceptions in the interval 1<Z<36?
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dlsoii
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(Original post by Mad Man)
Why do I have to fill in the 3d orbitals first? This contradicts the Aufbau principle. It doesn't say anything in my textbook, just to keep in mind that they are different. I'm doing AQA chemistry A level. Should I just learn these exceptions and are there any more of these exceptions in the interval 1<Z<36?
Yes, in this interval Cu and Cr are the only exceptions. Essentially, having a full or half full d subshell and a lone electron in the 4s orbital makes the atoms more stable than having a full 4s orbital and a partially filled d subshell. This has to do with the great amount of repulsion between the electrons of the 4s orbital and that 3d and 4s orbitals are close in energy level, enabling electron transfer from 4s to 3d.
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flowerscat
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Cu is [Ar] 3d¹⁰ 4s¹ and Cr is [Ar] 3d5 4s¹. This is because it is the most energetically favourable configuration for both the atoms (the configuration with the lowest energy)

Also, when the d-block form ions, electrons are removed from 4s first (though are are filled into 3d last).

When empty, 4s is of a lower energy level than 3d.
When full, 4s is of a higher energy level than 3d. Hence electrons are removed from 4s first.
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Pigster
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(Original post by Mad Man)
Why do I have to fill in the 3d orbitals first? This contradicts the Aufbau principle. It doesn't say anything in my textbook, just to keep in mind that they are different. I'm doing AQA chemistry A level. Should I just learn these exceptions and are there any more of these exceptions in the interval 1<Z<36?
I love the way people come on TSR and tell people that they understand about the fill order of 4s and 4d and their relative energies and why they fill the way they do. I love the way people are so certain they know and love to correct other people.

For a taste of why some of you may be wrong and a little way towards understanding what actually happens, have a read of this: http://ericscerri.blogspot.com/2012/...u-to-find.html
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dlsoii
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(Original post by Pigster)
I love the way people come on TSR and tell people that they understand about the fill order of 4s and 4d and their relative energies and why they fill the way they do. I love the way people are so certain they know and love to correct other people.

For a taste of why some of you may be wrong and a little way towards understanding what actually happens, have a read of this: http://ericscerri.blogspot.com/2012/...u-to-find.html
Thank you for the link! I was merely trying to relay what I have learned from my A-level studies to another A-level student. For the purposes of our specification (as infuriating as it may be) we simply need to be able to recall these exceptions, and at most give a vague, shaky explanation regarding atomic stability.

I'm going to read over the article now. Do you have any other recommendations for this topic? I'd love to gain a little more understanding.
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Pigster
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(Original post by dlsoii)
Thank you for the link! I was merely trying to relay what I have learned from my A-level studies to another A-level student. For the purposes of our specification (as infuriating as it may be) we simply need to be able to recall these exceptions, and at most give a vague, shaky explanation regarding atomic stability.

I'm going to read over the article now. Do you have any other recommendations for this topic? I'd love to gain a little more understanding.
Eric cites his references, they'd be a good start (assuming you want more after reading his blog post).
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dlsoii
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(Original post by Pigster)
Eric cites his references, they'd be a good start (assuming you want more after reading his blog post).
Yes, I've just seen that - I think I'll follow a few of them up.
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Mad Man
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(Original post by Pigster)
I love the way people come on TSR and tell people that they understand about the fill order of 4s and 4d and their relative energies and why they fill the way they do. I love the way people are so certain they know and love to correct other people.

For a taste of why some of you may be wrong and a little way towards understanding what actually happens, have a read of this: http://ericscerri.blogspot.com/2012/...u-to-find.html
I don't understand.
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Pigster
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(Original post by Mad Man)
I don't understand.
Don't understand what? The actual fill order rules? Why should you? It is not easy. Which is why so many teachers just teach the lazy Aufbau method.
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jack_harrison
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An important factor to consider which these elements is something called exchange energy. There is an inherent stability in having degenerate (same energy) electrons with the same spin. A half filled d-subshell has 5 electrons that are effectively identical, a full d-subshell has 2 sets of 5. I'd imagine that the stability obtained by favouring the half or fully filled subshell outweighs the energy required to promote the electron.
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