The d- and f-Block Elements
The d- and f-block domain tests electronic configurations, periodic trends, oxidation states, magnetic and catalytic behaviour, and the special stability of half-filled and fully filled subshells.
Transition metals and trends
A transition element has partly filled d orbitals in the atom or in a common oxidation state; Zn, Cd and Hg (d10) are not typical transition metals. Across the 3d series, atomic radius falls slightly at first then rises near the end; ionisation enthalpy generally increases; many oxidation states occur because 3d and 4s energies are close. Colour arises from d–d transitions; Sc3+ (d0) and Zn2+ (d10) are colourless.
Interstitial compounds and alloys
Small atoms such as H, C or N occupy interstitial sites, giving compounds that are hard, high-melting and often non-stoichiometric. Alloys such as brass and steel are substitutional or interstitial solid solutions. Transition metals are good catalysts because they provide variable oxidation states and adsorb reactants.
Lanthanoids and actinoids
Lanthanoid contraction is the steady decrease in size from La to Lu due to poor shielding by 4f electrons; it makes Zr and Hf similar. Ce4+ and Eu2+ are unusually stable. Actinoids show greater oxidation-state variety and more radioactivity.
Worked example
Mn (Z = 25) is [Ar]3d5 4s2; Mn2+ is [Ar]3d5. Five unpaired electrons give μ = √(n(n+2)) = √35 ≈ 5.9 BM. Reason: remove 4s electrons first for the ion, then count unpaired d electrons.
Mark-losing traps
Writing 3d electrons before 4s in the configuration of the atom, forgetting that 4s empties before 3d when cations form, assuming all d-block ions are coloured, and ignoring that Zn is not a typical transition metal are common mistakes.