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Offline Donaldson Tan

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Re: electron configuration
« Reply #15 on: May 28, 2006, 12:32:47 AM »
3d5 4s2 is more stable than the 3d7 4s0 configuration because it describes a half-filled 3d sub-shell. The 3d5 configuration minimise electronic repulsion within the atom.
« Last Edit: May 28, 2006, 11:37:44 AM by geodome »
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Offline rleung

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Re: electron configuration
« Reply #16 on: May 28, 2006, 10:28:17 AM »
If this were true, would that mean that all Group 9 elements exhibit this behavior? (eg. when a 2+ ion is fomed from any group 9 element, electrons come off the d-subshell first in order to create a more stable configuration, namely, a half-filled d subshell).  This goes against everything I have been taught since I have always been taught that s-subshell electrons are always removed before d-subshell ones.

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Offline Dan

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Re: electron configuration
« Reply #17 on: May 28, 2006, 10:42:37 AM »
The configuration of Co (II) in solution is definately d7, you can tell from the magnetic moment. Maybe the configuration for the free gaseous ion is 4s23d5, I'm not sure, but it's an idea.
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Offline rleung

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Re: electron configuration
« Reply #18 on: May 28, 2006, 10:58:23 AM »
How can you tell from a magnetic moment?  3d7 and 3d5 are both paramagnetic, so wouldn't they give you the same result?

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Offline Will

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Re: electron configuration
« Reply #19 on: May 28, 2006, 11:00:11 AM »
3d5 4s2 is more stable than the 3d7 configuration because it describes a half-filled 3d sub-shell. The 3d5 configuration minimise electronic repulsion within the atom.

Well it depends on the ligands, if there were SFLs then the repulsion would cause the 3d5 electrons to spread accross the 3dxy 3dxz and 3dyz orbitals (lower energy) with empty 3dz^2 and 3dx^2-y^2 orbitals (higher energy), but a full 4s orbital. (Only one unpaired electron in this case).

If it were just 3d7, 5 electrons could spread accross the lowere energy orbitals, and 2 could spread accross the higher energy 3d orbitals, which would have 3 unpaired electrons!

Anyway the 3d5 4s2 configuration is only theoretical when talking about these (non-gaseous!) cations, whether this is lower energy (taking ligands into account!) or not, no one will know!

Offline Mitch

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Re: electron configuration
« Reply #20 on: May 28, 2006, 11:01:13 AM »
The 4s subshell is not lower in energy then the 3d!!!

There is a difference between the energy of a subshell and the configuration enery
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Offline Will

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Re: electron configuration
« Reply #21 on: May 28, 2006, 11:08:27 AM »
The 4s subshell is not lower in energy then the 3d!!!

I need new chemistry teachers then! :D

Offline Dan

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Re: electron configuration
« Reply #22 on: May 28, 2006, 11:26:03 AM »
How can you tell from a magnetic moment?  3d7 and 3d5 are both paramagnetic, so wouldn't they give you the same result?

How can you tell from a magnetic moment?  3d7 and 3d5 are both paramagnetic, so wouldn't they give you the same result?

They are both paramagnetic, but

Eff. Mag. Moment = 2[S(S+1)]1/2            (spin only approx)

But, d5 low spin and d7 low spin give the same result (S=1/2 for both), however the Eff. Mag. Moment of d5 low spin will be temperature dependant, but d7 low spin will not be (first order orbital effects).

d5 high spin will have a slighty higher eff mag moment than high spin d7 (but this could be masked by orbital effects). The Eff. Mag. Moment of d7 high spin will be temperature dependant, but d5 high spin will not be (first order orbital effects).

Also high spin d5 gives only very very weak d-d spectra, since all d-d transitions in d5 high spin are spin forbidden, but the d-d spectra for d7 (high or low spin) is quite a bit stronger.

Guess who's been revising spectra and magnetism today...
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Offline Dan

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Re: electron configuration
« Reply #23 on: May 28, 2006, 11:31:40 AM »
The 4s subshell is not lower in energy then the 3d!!!

For charged transition metals, I agree with you.
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Offline Mitch

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Re: electron configuration
« Reply #24 on: May 28, 2006, 12:01:58 PM »
The reason why electrons fill the 4s subshell before the 3d is because the 3d electrons are closer to the nucleus and will repel each other in the 3d more strongly then if they were in the higher energy and larger orbit of the 4s subshell. So yes, the 3d is lower in energy, but the energy of configuration would be lower if the electrons occupied the 4s.
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Offline Will

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Re: electron configuration
« Reply #25 on: May 28, 2006, 12:12:36 PM »
The reason why electrons fill the 4s subshell before the 3d is because the 3d electrons are closer to the nucleus and will repel each other in the 3d more strongly then if they were in the higher energy and larger orbit of the 4s subshell. So yes, the 3d is lower in energy, but the energy of configuration would be lower if the electrons occupied the 4s.

Ahh! Thanks Mitch, that explains a lot! ;)

So would the ligands in charged transition metal complexes repel the 3d electrons more than 4s electrons?

Offline Donaldson Tan

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Re: electron configuration
« Reply #26 on: May 28, 2006, 12:23:41 PM »
How can Co(II) be 3d7 if it has lost 2 electrons?
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Offline Will

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Re: electron configuration
« Reply #27 on: May 28, 2006, 12:29:25 PM »
How can Co(II) be 3d7 if it has lost 2 electrons?

Because cobalt loses its two 4s electrons. So: [Ar]3d74s2 goes to [Ar]3d7. I'm not 100% sure though, what do you think Co(II)'s configuration is?

Offline Mitch

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Re: electron configuration
« Reply #28 on: May 28, 2006, 12:34:48 PM »
How can Co(II) be 3d7 if it has lost 2 electrons?

Because cobalt loses its two 4s electrons. So: [Ar]3d74s2 goes to [Ar]3d7. I'm not 100% sure though, what do you think Co(II)'s configuration is?

makes sense to me.
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