A Level Chemistry OCR Practice Exam

What is the primary purpose of oxidation numbers in chemistry?

1. A measure of an atom's size

2. A measure of the number of electrons an atom uses to bond

3. A measure of an atom's mass

4. A measure of the atom's temperature

The correct answer is: A measure of the number of electrons an atom uses to bond

The primary purpose of oxidation numbers in chemistry is to indicate the number of electrons that an atom can lose, gain, or share when it forms chemical bonds. They are used as a tool to keep track of electron transfer in redox reactions and to understand the bonding and chemical behavior of different elements in compounds. By assigning oxidation numbers, chemists can determine how different atoms interact based on their electron configurations and assess the changes in oxidation state during a reaction, which is foundational in predicting the outcome of chemical processes. In contrast to the other choices, oxidation numbers do not relate to an atom's size, mass, or temperature. For instance, the concept does not involve measuring an atom's physical dimensions or its thermal properties. Hence, oxidation numbers specifically provide insights into electron involvement in bonding rather than other attributes of atoms.