d-Block and f-Block Elements
This section covers d-Block and f-Block Elements: transition-element definitions, electronic configurations, variable oxidation states, colour, magnetism, catalysis, alloy formation, lanthanoid contraction and actinoid behaviour. Expect comparisons and structure–property reasoning.
Core rules
- A transition element has an incomplete d subshell in its atom or in a common oxidation state. Zn, Cd and Hg are not typical transition elements because their d subshells are full.
- Variable oxidation states arise from similar 4s and 3d energies; Mn shows +2 to +7.
- Colour arises from d–d transitions; magnetic moments use μ = √(n(n+2)) BM for n unpaired electrons.
- Lanthanoid contraction is the steady decrease in size across the lanthanoids due to poor shielding by 4f electrons.
Worked example
Calculate the spin-only magnetic moment of Fe³⁺. Fe is [Ar]3d⁶4s², so Fe³⁺ is [Ar]3d⁵. A high-spin d⁵ ion has five unpaired electrons. μ = √(5 × 7) = √35 = 5.92 BM. This large moment helps distinguish high-spin Fe³⁺ from low-spin Fe³⁺ complexes, which have one unpaired electron and μ = 1.73 BM.
Traps
Do not treat Zn as a typical transition element; check Cr and Cu configurations; do not assume every d-block ion is coloured; remember that Sc³⁺ has no d electrons and is colourless; do not confuse lanthanoid contraction with actinoid contraction.