Answer to Question #136683 in General Chemistry for Tatiana

Question

How can oxidation numbers help you determine a redox reaction? When are oxidation numbers used instead of a valence number?

Answer 1

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron. Redox reactions are common and vital to some of the basic functions of life, including photosynthesis, respiration, combustion, and corrosion or rusting.

The oxidation state or oxidation number is a number given to each atom based on the electron assignments. In order to identify redox reactions using oxidation states, oxidation states are assigned to each atom in the reaction. A change in oxidation state for the atoms indicates a redox reaction.

Metals, which commonly donate electrons and form compounds in which they exist in the positive, or cationic, state, are assigned positive oxidation numbers. For a metal such as zinc, which donates two electrons to achieve a stable electron configuration, the oxidation number is $+2$ . Nonmetals, which commonly accept electrons and in compounds exist in the negative, or anionic, state, are assigned negative oxidation numbers. The oxidation number is $-1$ for chlorine and the other halogens, which accept one electron to complete their valence shell.