The oxidation number of a substance is the charge on an atom in the molecule or ion. It is equal to the number of electrons lost or gained by an atom. In this case, sulfur loses two electrons, so its oxidation number is -2.
There are several rules for assigning oxidation numbers to atoms in a molecule or ion:
If there is only one atom of a certain element in the molecule or ion, give it an oxidation number of zero (it has lost no electrons). For example, carbon monoxide has a formula C(O) and consists entirely of carbon atoms each with an oxidation number of zero.
For every other atom besides oxygen and hydrogen in CO, assign it an oxidation number equal to its valence electron count (the maximum number of electrons that it can lose). For example, nitrogen has five valence electrons and oxygen has six valence electrons, so each nitride and peroxide should be assigned an oxidation number +5 and +6 respectively.
If there are more than one atom of any given element present in the compound then give each one an individual oxidation.
Last modified: November 1, 2022