[maccha]

So in my textbook there's an example that shows:

MnO4- + 5e- ---> Mn2+

(unbalanced)

and it says: in this situation MnO4 is undergoing reduction. I thought, however, that you it would just be Mn undergoing reduction. I thought you just looked at each atom individually? Can someone please clarify? Thanks!

[ARGOS++]

Dear maccha;

Permanganate is a strong oxidizing agent and so itself must undergo reduction, in this case from +7  to the +2 oxidizing state according to:
                         http://en.wikipedia.org/wiki/Permanganate 
(There is also a balanced reaction equation.)

As you may also see, that only Mn changes in the half-reaction its oxidizing state.

Good Luck!
                    ARGOS⁺⁺

[Borek]

I thought you just looked at each atom individually?

No, it is whole molecule that reacts. Note, that without the 4 oxygens there will be no permanganate. Also note, that oxidation number (+7) assigned to Mn in MnO₄^- doesn't reflect any measurable property of the atom in the compound.

[maccha]

Okay thank you very much that really helps. Further to that, do you just look at the initial and final oxidation number of Mn to know if it's reduction, rather than the charge of the entire molecule?

[ARGOS++]

Dear maccha;

Oxidation numbers are formal numbers and not measurable. You may see below how to apply them to molecules and atoms:
          http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson52.htm 

If it will be oxidized/reduced depends on the half-reaction and the electrons involved according to:
          http://en.wikipedia.org/wiki/Reduction-oxidation 
Recognise specially the explained rules therein!

Good Luck!
                    ARGOS⁺⁺