Oxidation Number Rules

 

General Rules

 

1.      For an atom in its elemental form, oxidation number = 0.

 

2.      For a monoatomic ion, oxidation number = ion charge

 

3.      The sum of the oxidation numbers for all atoms in a neutral compound equals zero.

 

4.      The sum of the oxidation numbers for all atoms in a polyatomic ion equals the charge on the ion.

 

 

 

     Rules for specific atoms in compounds:

 

 

      Atom or Group                          Oxidation Number

Group 1A cation                                    +1

 

Group 2A cation                                    +2

 

Hydrogen                            +1 in combination with nonmetals

                                             -1 in combination with metals or boron

 

Fluorine                                                  -1

 

Oxygen                                         -1 in peroxides

                                                      -2 in all other compounds