Oxidation Numbers

[yusufhamood]

Does oxygen have an oxidation number of -2 or is it -4 since there are 2 oxygen's? Also does the number in front count towards the oxidaton number

Thanks in advance 

[Bell9565]

Does oxygen have an oxidation number of -2 or is it -4 since there are 2 oxygen's? Also would that make the oxidation number of 2O2 -8 or -4

Thanks in advance 

If it is by itself eg O2 like as the gas, the oxidation number is 0. It is only -2 when it is in ion form.

[Sine]

Does oxygen have an oxidation number of -2 or is it -4 since there are 2 oxygen's? Also would that make the oxidation number of 2O2 -8 or -4

Thanks in advance 

oxidation numbers of neutral substances of a single element is 0 e.g. O2, N2, O3

For 2O2 we really only consider O2 since mole ratios don't matter. Hence as above the oxidation number is 0.

EDIT: as above oxygen has an oxidation number of -2 (when in an multi-element compound). The exception is oxygen has an oxidation number of -1 in a peroxide e.g. H2O2

[TheAspiringDoc]

In CO₂, each Oxygen atom has an oxidation number of -2, so since there are two Oxygen atoms per CO₂ molecule the total effect of both Oxygens is combined to give a sum oxidation number of -4 (which balances out Carbon's +4 oxidation number - and is why CO2 is neutrally (I.e. Not) charged overall)

Hope this hælps 

[Yertle the Turtle]

Oxidation number rules are as follows:
All complete molecules or elements have an overall oxidation number of zero
In general the oxidation numbers of ions are the charges on the ions.
There are a couple of exceptions to these two main rules, but to apply them, you add the oxidation numbers of all atoms within the molecule (this includes having multiple of one element within the molecule), however there is no need to factor in the coefficients of the molecules.

[MAGGOT]

[Rule 5] Oxygen=-2 (except H2O2 or f=-1)  ← oxygen ion
[Rule 1] If bonded with itself, oxidation number of oxygen is 0