How To Calculate Oxidation States

The oxidation state of a molecule or compound shows the overall charge of the species being observed. Oxidation states allow a large amount of information to be inferred from a compound or ion. Information such as potential reactivity, compound composition and molecular structure can be inferred with relative accuracy given the oxidation states of one or more of the constituent species. The determination of oxidation states is often first encountered in introductory chemistry courses.

Step 1

Determine the overall charge of the compound or ion being observed. The overall charge of the entire compound is generally located in the upper-right corner of the compound name. If no charge is written, it is assumed to be a neutral compound.

Step 2

Determine the oxidation state of any species within the compound that are static. For example, oxygen, in virtually all cases, has a charge of minus 2. Fluorine is another example of a static oxidation state whose value is minus 1. Further static oxidation states are located on the periodic table by group number.

Step 3

Multiply the static oxidation states by the number of atoms found within the compound. For example, Na2SO4 has two sodium (Na) atoms with an oxidation charge of plus 1 each and an overall oxidation value of plus 2.

Step 4

Add together the oxidation values for all known species.

Step 5

Subtract the summed value from the overall charge of the compound. For example, Na2SO4, Na2 yields 2 (plus 1) + 4(minus 2) = minus 6. Subtracting minus 6 from the neutral value of 0 yields 0 – (minus 6) = 6. This final value is the oxidation state of the unknown element, in this case sulfur.