Oxidation Number Rules Flashcards Preview

Free (uncombined) elements have an oxidation number of zero

This includes polyatomic elements

Monatomic ions:
Oxidation number = charge of ion

Oxygen:

Usually -2

Exceptions:
Hydrogen peroxide: H₂O₂ (-1)
Peroxide ion: O₂^2- (-1)

Hydrogen:

Oxidation = +1

Except when bound to metals in binary compounds (-1)

Group 1A:

+1

Group 2A:

+2

Al (Group 3A):

+3

F (Group 7A):

-1

Molecular formula or formula unit:

Oxidation number sum must equal zero

Polyatomic ions:

Sum of oxidation numbers must = ion charge

Can be integers or fractions

E.g. one O in O₂^- = -1/2