Final answer:
Oxidation numbers are assigned to atoms to indicate their degree of oxidation or reduction in a chemical reaction. The rules for assigning oxidation numbers involve elements in their elemental state and monatomic ions. In a reaction, the oxidation or reduction can be determined by comparing the change in oxidation numbers of the atoms involved.
Step-by-step explanation:
The oxidation number is a positive or negative number that is assigned to an atom to indicate its degree of oxidation or reduction in a chemical reaction. There are rules for assigning oxidation numbers:
- Atoms in their elemental state are assigned an oxidation number of 0.
- Atoms in monatomic (i.e., one-atom) ions are assigned an oxidation number equal to their charge.
- The sum of oxidation numbers in a neutral compound is 0.
- In polyatomic ions, the sum of oxidation numbers is equal to the charge of the ion.
To assign oxidation numbers, you can apply these rules to each atom in a compound or ion. For example, in the reaction Sr + SO3 -> SrSO3, Sr is being reduced (+0 to +2 oxidation number) and SO3 is being oxidized (+6 to +4 oxidation number).