Final answer:
An oxidation number indicates the degree of oxidation or reduction of an atom, representing the net number of electrons lost or gained. Positive oxidation numbers indicate a loss of electrons, while negative numbers indicate a gain. They are essential in understanding electron movement in oxidation-reduction reactions.
Step-by-step explanation:
An oxidation number is a positive or negative number assigned to an atom in a molecule or ion. This number represents the atom's degree of oxidation or reduction, which essentially means the net number of electrons that have been gained or lost to achieve its current state. If an atom loses electrons, it becomes more positive in charge, therefore its oxidation number increases. For example, when magnesium (Mg) reacts to form MgCl2, it loses two electrons and thus has an oxidation number of +2. Conversely, each chlorine atom gains one electron and has an oxidation number of -1. Oxidation involves an increase in oxidation number, while reduction involves a decrease. Oxidation numbers help us to track the movement of electrons in chemical reactions, especially in oxidation-reduction (redox) reactions. There are specific rules that can be used to assign oxidation numbers to atoms in compounds. For instance, in a molecule of water (H2O), hydrogen has an oxidation number of +1 and oxygen has an oxidation number of -2. It's important to note that these are not actual charges on the atoms, but are used for bookkeeping during chemical reactions.
Incorrect statement correction: The oxidation number of oxygen in water is actually -2, not +2 as previously stated. This indicates that each oxygen atom has 'gained' a total of two electrons from the hydrogens, one from each.