CHEMISTRY COMMUNITY

What exactly are oxidation numbers and how do you find them for elements?

Oxidation numbers are numbers you assign to an element in chemical combination that represents the number of electrons lost (or gained, if the number is negative) by an atom of that element in the compound.

To find oxidation numbers...
1) The oxidation number of a free element is always 0.
2) The oxidation number of a monatomic ion equals the charge of the ion.
3) The oxidation number of H is +1, but it is -1 in when combined with less electronegative elements.
4) The oxidation number of O in compounds is usually -2, but it is -1 in peroxides.

Element by itself = 0 Monatomic Ion = ion charge
Group 1A = always +1
Group 2A= always +2
Halogens= usually -1, positive with oxygen
Hydrogen= +1 with nonmetals
-1 with metals
Oxygen= usually -2, -1 with peroxide ((H2O2)
Fluoride= always -1

* I recommend you to watch Tyler DeWitt in Youtube if you are still having some trouble finding oxidation numbers. He goes over some examples.

An oxidation number is a number assigned to an element in chemical combination. It represents the number of electrons lost/gained by an atom of that element in the compound.

https://www.khanacademy.org/science/che ... ion-states

This video also gives some helpful examples that are worked out for you.