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Oxidising power of the halogens

These three features effect the oxidising power:
the strength of the x-x (eg f-f) bond
the affinity of an x atom for an electron
the energy released when the x- ion goes into solution or into a crystal lattice
is it possible someone could explain this with the relevant examples?
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R T
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Original post by ss2525
These three features effect the oxidising power:
the strength of the x-x (eg f-f) bond
the affinity of an x atom for an electron
the energy released when the x- ion goes into solution or into a crystal lattice
is it possible someone could explain this with the relevant examples?

I don't know about examples but I can try to explain this.

A very good oxidizing reagent is a molecule or atom that loves to tear electrons away from stuff. In general terms, it pulls electrons towards itself very well.

So a powerful oxidising reagent will form a strong X-X bond. Because both X pull on the electron very hard, it is difficult to disrupt this. Imagine two people holding each others arms very hard vs. two people only weakly touching - it's obvious which of the two would be harder to separate.
Now in terms of bond strength, from memory i think
F-F is roughly 160kj/mol
Cl-Cl is 240
Br-Br is 190
I-I is 160

We would expect F-F to be the strongest, and it should be. The reason F-F is low is due to complicated MO reasons, but basically F is too small and experiences too much overlap repulsion from its electrons.


Likewise, if a powerful oxidising reagent wants electrons, it will have a high affinity for them.
From memory the affinities are roughly
F = -330 kj/mol
Cl = -340
Br = -320
I = -300
again F is lower than it should be due to molecular orbital problems.

This feeds into the last point - a powerful oxidising reagent will be comfortable with holding a -ve charge. This will be more energetically favourable the better the oxidising power is.
Again, from memory
F is -760 kj/mol
Cl is -600
Br -550
I -500
Which now makes sense.
The above is also consistent with reduction potentials.


Not sure if i've mixed up my numbers, but the basic principle is that F is the best because F is as close as we get to a very positive, nearly naked atom. F gives some odd energies due to extreme contractions, but you can ignore that until you go to university if I remember correctly.

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