IB Chemistry - Oxidation

IB Chemistry home > Syllabus 2025 > Redox processes > Reactions involving electron transfer

Chemical reaction may be classified according to what is happening to the reactants during the process, or the type of products formed. Oxidation state, or number, is a theoretical construct used to provide a rationale for certain chemical processes, which do not fit easily into other, more mainstream, types of reaction.

In redox reactions it is suggested that electrons are 'more attached' to electronegative atoms than to electropositive atoms. We will never know for sure whether or not this is the case, but it provides a useful model to help us explain the driving force behind one class of reactions, oxidation and reduction.

Syllabus reference

Reactivity 3.2.1 - Oxidation and reduction can be described in terms of electron transfer, change in oxidation state, oxygen gain/loss or hydrogen loss/gain.

  • Deduce oxidation states of an atom in a compound or an ion.
  • Identify the oxidized and reduced species and the oxidizing and reducing agents in a chemical reaction.


  • Include examples to illustrate the variable oxidation states of transition element ions and of most main group non-metals.
  • Include the use of oxidation numbers in the naming of compounds

Tools and links

  • Structure 3.1 - What are the advantages and limitations of using oxidation states to track redox changes?
  • Structure 2.3 - The surface oxidation of metals is often known as corrosion. What are some of the consequences of this process?

In Chapter 9.1