Final answer:
The oxidation number is an indicator of an atom's degree of oxidation or reduction; it reflects a partial gain or loss of electrons and is essential for tracking electron transfer in redox reactions.
Step-by-step explanation:
The oxidation number, also known as the oxidation state, is a positive or negative number that is assigned to an atom to indicate its degree of oxidation or reduction. In a chemical reaction, particularly in oxidation-reduction (redox) reactions, oxidation numbers help us keep track of the electron transfers that occur.
Oxidation involves the loss of electrons and an increase in oxidation number, while reduction involves the gain of electrons and a decrease in oxidation number. When assigning oxidation numbers, there are rules to follow such as the oxidation number of any pure element being zero, and the sum of oxidation numbers in a neutral compound being zero. For elements in compounds, the oxidation number corresponds to the hypothetical charge an atom would have if the compound was entirely ionic.
For example, in sodium chloride (NaCl), the sodium ion has an oxidation number of +1, whereas the chloride ion has an oxidation number of -1. This illustrates how the total sum of oxidation numbers for the compound is zero, which aligns with its neutral charge. By carefully assigning oxidation numbers, chemists can better understand how electrons are redistributed in redox reactions, which is fundamental to many areas of chemistry, including electrochemistry.