S3.1.7  Discontinuities occur in the trend of increasing first ionization energy across a period. (AHL)

S3.1.8  Transition elements have incomplete d-sublevels that give them characteristic properties. (AHL)

S3.1.9  The formation of variable oxidation states in transition elements can be explained by the fact that their successive ionization energies are close in value. (AHL)

S3.1.10  Transition element complexes are coloured due to the absorption of light when an electron is promoted between the orbitals in the split d-sublevels. The colour absorbed is complementary to the colour observed. (AHL)

Nature of science, Structure 2.3—What are the arguments for and against including scandium as a transition element? (AHL)

Reactivity 3.4—What is the nature of the reaction between transition element ions and ligands in forming complex ions?

Tool 1, Inquiry 2—How can colorimetry or spectrophotometry be used to calculate the concentration of a solution of coloured ions?