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electron configuration with 3d and 4s...

Submitted by sshiber on 9 December 2005 - 12:05pm.

a few questions:
1. what is the reason that the electrons fill 4s and then 3d (I need a energy explanation)

2.why are Cu, Cr exceptional from what I wrote in question 1? and what does it say about their electron configuration in there ion state(from where will the electron be removed first frome 3d or 4s)?

3.is taking out electrons from non metal elements with 4S and 3d in their electron configuration the same as in transitionl metals(first comes out from 4S then from 3d)?

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allan_chemist's picture

Re: electron configuration with 3d and 4s...

Submitted by allan_chemist on 9 December 2005 - 12:28pm.

sshiber wrote:
2.why are Cu, Cr exceptional from what I wrote in question 1? and what does it say about their electron configuration in there ion state(from where will the electron be removed first frome 3d or 4s)?

I think you still remove the first electron from the 4s, because by then that orbital is higher in energy than the 3d electrons.

Cu and Cr are exceptions because of spin pairing etc.

To pair spins, you need to sacrifice a little 'exchange energy', because you have two electrons occupying the same orbital. For Cr, you have a choice of 2x4s electrons, paires, with 4x3d electrons, all unpaired, OR just one 4s electron, unpaired, and five 3d electrson, all unpaired. They all have paralled spins, obeying one of Hund's (or is it Hunds'?) rules, and it is energetically more favourable.

For Cu, it is just a case of it being better to fill the whole of the 3d shell, which by now is WAY lower in energy than the 4s. You have to pair in either the 4s or the 3d, but because 3d is lower in energy, it is more favourable.

I hope that hand-waving argument is clear enough.

I'll let seombody else look at the other two questions..

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feline1's picture

Re: electron configuration with 3d and 4s...

Submitted by feline1 on 9 December 2005 - 12:38pm.

sshiber wrote:
1. what is the reason that the electrons fill 4s and then 3d (I need a energy explanation)

well cos they're lower in energy!
And indeed why shouldn't they be, etc etc 8)

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allan_chemist's picture

Submitted by allan_chemist on 9 December 2005 - 12:55pm.

3d contract faster than 4s, but 4s *start* at a lower energy, rapidly being overtaken by 3d.
Right?

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feline1's picture

Submitted by feline1 on 9 December 2005 - 1:25pm.

well yeah,
but then bear in mind that this means we accept "the orbital approximation", which is this fantasy where there are separate discrete individual "orbitals" sitting around like little containers for pairs of electrons.

A more "real" way to think of it is "well, this is what we calculate the energy will be if we give *these* few dozen electrons *these* amounts of angular momentum etc etc

i.e., orbitals themselves aren't physical entities which have inherent energies

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