OXIDATION NUMBERS

An oxidation number is the charge that an atom in a compound would have if the electron pairs in the bond belonged solely to the more electronegative atom.

1. The oxidation # of an atom in its pure form, such as Na or Fe, or in a

molecule of that element only, such as O2 or P4,

is ZERO.

2. The oxidation # of a monatomic ion is the charge on the ion.

ex. Ca2+ is +2

3. a) O = -2 except in H2O2 (-1)

b) H = +1 except in metal hydride, ex. LiH (-1)

c) Group IA = +1d) Group IIA = +2e) Halides = -1

4. Use charges on polyatomic ion as indicator, examples: SO4

2- , NO3-

The algebraic sum of the positive & negative oxidation #’s of the atoms in a polyatomic ion is equal to the charge on the ion.

example: SO42-

5. The sum of the positive & negative oxidation #’s in a neutral compound is zero.

example: K2Cr2O7

1. What is the single oxidation number of manganese (Mn) in:

a) MnO2

b) Mn2O7

c) MnO42-

d) KMnO4

2. Determine the single oxidation # of the underlined atom in each of the following species:

a) CrO42-

b) P4O10

c) Fe3O4

d) S2O32-