Transition metals (A-level only)

Transition metals are elements found in the d-block of the periodic table, specifically in groups 3–12, that form at least one stable ion with a partially filled d-subshell. This unique electronic configuration gives rise to their characteristic properties: variable oxidation states, formation of coloured compounds, catalytic activity, and the ability to form complex ions. In AQA A-Level Chemistry, you will explore how these properties arise from the splitting of d-orbitals in ligand fields, leading to d-d transitions that absorb visible light and produce colour. Understanding transition metals is essential for explaining phenomena such as the catalytic role of iron in the Haber process or the use of platinum in catalytic converters.

Transition metals are central to many industrial and biological processes. For example, haemoglobin contains iron(II) ions that reversibly bind oxygen, while vitamin B12 contains cobalt. On the curriculum, you will learn to write electronic configurations for atoms and ions of transition metals (e.g., Sc to Zn), predict oxidation states, and explain trends in stability. You will also study ligand substitution reactions, the chelate effect, and how complex ions can be identified using colorimetry. This topic builds on earlier work on atomic structure, bonding, and redox chemistry, and it connects to practical applications in medicine, catalysis, and materials science.

Mastering transition metals requires a solid grasp of d-orbital splitting in octahedral and tetrahedral fields, and how this relates to colour and magnetic properties. You will need to recall that the colour observed is complementary to the wavelength absorbed, and that factors like ligand type, oxidation state, and coordination number affect the colour. Additionally, you should be able to explain why transition metals exhibit catalytic activity—both heterogeneous (e.g., Fe in Haber) and homogeneous (e.g., Mn²⁺ in autocatalysis of oxalate by permanganate). This topic is a favourite for exam questions that test your ability to apply theory to unfamiliar contexts, so practice with past papers is key.