Chapter 6 introduces redox chemistry as a unified framework built on the transfer of electrons and changes in oxidation state. Though relatively concise at AS Level, the concepts developed here underpin a substantial portion of both the inorganic and physical chemistry that follows, and precision in their application is essential.

The chapter establishes a systematic method for calculating oxidation numbers of elements in compounds and ions, and uses changes in oxidation number as a tool for balancing chemical equations. The terms oxidation, reduction, redox and disproportionation are defined in terms of both electron transfer and oxidation number change, and the roles of oxidising and reducing agents are identified and distinguished. Roman numerals are used throughout to denote oxidation states unambiguously.