Can Atoms Have Fractional Oxidation States?

[futuredoctor10]

Is it true that the oxidation state of an atom in a Lewis structure is always an integer?

What is the oxidation state of carbon in C6H8O6?

6x + 8 + (-2)(6) = 0
6x = 4
x = 4/6 or 2/3?

---

Members don't see this ad.

 

[engineeredout]

The answer is yes. Oxidation states are not as rigid as people would like. The 2/3rds is an average oxidation state

 

[futuredoctor10]

Cool thanks! Hopefully it won't come up on the MCAT but just be aware you can have a fractional oxidation state I guess?

Just wondering where you got this info from (textbook, college prof, MCAT text)? Rules I have found say to avoid fractional oxidation states UNLESS you are not talking about the "Formal" Oxidation state (and considering resonance).

 

[ThePandaFactor]

No it is not possible. Oxidation state is defined as an integer.

 

[IvyLeagueThug]

No it is not possible. Oxidation state is defined as an integer.

This is incorrect.

You can, indeed have fractional oxidaiton numbers.

I learned the hard way, as this actually appeared on the PS section of the June 13th exam.

 

[ThePandaFactor]

Ok well there are a few cases where it is useful, like when the molecule is made up of all the same atom, so it's kind of like resonance. But in the case he was talking about it is not.

 

[engineeredout]

Ok well there are a few cases where it is useful, like when the molecule is made up of all the same atom, so it's kind of like resonance. But in the case he was talking about it is not.

Useful or not, its the truth.

Just wondering where you got this info from (textbook, college prof, MCAT text)? Rules I have found say to avoid fractional oxidation states UNLESS you are not talking about the "Formal" Oxidation state (and considering resonance).

Just general knowledge floating around in my head, I haven't seen it in any mcat review that I've done. IF you actually draw out the lewis structure of C6H8O6 (which is ascorbic acid or Vitamin C btw) then you'll see that the carbon atoms have different oxidation states.

 

[futuredoctor10]

Thanks for the post, engineeredout. It actually came up as a discrete, which required knowing how to find such a fractional oxidation state to determine if a reaction was a redox reaction or not!

Also C3H8 would be another example right? Carbon's oxidation state is:
3x + 8 = 0
3x = -8
x = -8/3

OK cool got it now. Just seemed really odd initially to say "oh carbon has a -8/3 oxidation state" but it is possible, and now I know. Thanks everyone