Physical Chemistry Q: Do conduction band electrons affect chemical properties?

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uby
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Warning: I'm not a practicing chemist. Answers in as-simple-as-possible language (but not oversimplified!) would be greatly appreciated!

I'd like to know if the chemical properties of a solid can be affected by conduction band electrons. I assume that, in the majority of cases (and perhaps all cases?), it is the valence band electrons that dominate how a material chemically behaves (e.g. - reactivity).

As far as I know, conduction band electrons do not directly contribute to interatomic/molecular bonding and thus do not affect the stability of the solid. Is this correct?

Thanks!
 

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  • #2
DrDu
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Bonding is dominated by the valence band, but reactivity depends on the conduction band. Think of the process of formation of ions from a metallic electrode in a battery.
 
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uby
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Thanks for your reply, DrDu!

I'm not sure I agree with your first statement "reactivity depends on the conduction band" if it's meant to be general.

Would it be more precise to amend it to say "reactions between solids and charged species such as ions depend on the conduction band when electronic transport must occur to satisfy charge neutrality"? Otherwise, I'm not sure that electrons in the conduction band play ANY role at all in chemical reactions.

For example, if a metal wire is placed in a reactive acid bath (not to be confused with a corrosion half-cell - no electrode/counterelectrode arrangement, just a single wire), I wouldn't expect its reaction rate to change if a current was running through it or not.

ETA: Perhaps using a metal as an example is a bad idea, as it becomes difficult to distinguish valence from conduction band. Please replace the suggestion of a metal wire with a suitable semi-conductor to get the same idea across.
 
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DrDu
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Maybe you should confer a book on electrochemistry kinetics, especially Marcus theory.

However, I don't see why in a metal it should be difficult to distinguish valence from conduction band. As metals conduct electricity, the electrons are by definition in the conduction band.
But if you insist on considdering substances with well separated mainly anti-bonding conduction bands and bonding valence bands, these are mostly non-metals. They typically get reduced. E.g. think of the dissolution of iodine in a solution of sulfite. The first step will be a transfer of electrons from sulfite into the conduction band of iodine which leads to a breaking of the iodine bond of some molecules on the surface.
 
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Gokul43201
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For example, if a metal wire is placed in a reactive acid bath (not to be confused with a corrosion half-cell - no electrode/counterelectrode arrangement, just a single wire), I wouldn't expect its reaction rate to change if a current was running through it or not.
Running a current through a metallic wire does not change the number of conduction electrons in it.
 
  • #6
uby
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Running a current through a metallic wire does not change the number of conduction electrons in it.
True. I believe the same cannot be said about semi-conductors, as the application of a voltage will promote some valence band electrons into the conduction band in order to induce flow.
 
  • #7
uby
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Maybe you should confer a book on electrochemistry kinetics, especially Marcus theory.

However, I don't see why in a metal it should be difficult to distinguish valence from conduction band. As metals conduct electricity, the electrons are by definition in the conduction band.
But if you insist on considdering substances with well separated mainly anti-bonding conduction bands and bonding valence bands, these are mostly non-metals. They typically get reduced. E.g. think of the dissolution of iodine in a solution of sulfite. The first step will be a transfer of electrons from sulfite into the conduction band of iodine which leads to a breaking of the iodine bond of some molecules on the surface.
Thanks again DrDu! I will investigate Marcus theory -- although my cursory review seems to indicate that it deals with purely electron transfer reactions rather than redox reactions involving bond fission/reformation. Perhaps it has been modified to take this into account?

Ideally, I'd like to be able to correlate the density of electron states with reactivity in a redox reaction involving breaking/forming new bonds.
 

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