The d- and f-Block Elements
The d-block (groups 3-12) occupies the large middle section of the periodic table; in its elements the inner (n-1)d orbitals are progressively filled. The f-block (lanthanoids and actinoids) sits at the bottom, with 4f and 5f orbitals filling progressively.
Position and configuration
- Four d-series: 3d (Sc-Zn), 4d (Y-Cd), 5d (La, Hf-Hg) and 6d (Ac, Rf-Cn).
- General outer configuration: (n-1)d1-10 ns1-2 (exception Pd = 4d10 5s0).
- Anomalies: Cr = 3d5 4s1 and Cu = 3d10 4s1 (extra stability of half-filled and fully-filled d sets).
- IUPAC: a transition metal has an incomplete d subshell in the atom or in an ion. Zn, Cd, Hg (d10) are not regarded as transition metals.
General trends (3d series)
- Metallic character: hard, high m.p./b.p. (except Zn, Cd, Hg), high enthalpy of atomisation peaking near the middle (one unpaired e- per d orbital favours strong bonding).
- Ionisation enthalpy: increases left to right but the variation is much smaller than in non-transition elements.
- Atomic/ionic radii: small decrease across a series; 4d > 3d, but 5d nearly equals 4d due to the lanthanoid contraction (Zr 160 pm, Hf 159 pm).
- Oxidation states: variable, differing by unity; maximum range at the middle (Mn: +2 to +7); lowest common state +2.
- Colour: from d-d transitions (ions with d1-d9); d0 and d10 ions are colourless.
- Magnetism: paramagnetism from unpaired electrons; spin-only mu = sqrt(n(n+2)) BM.
- Also: catalytic activity, interstitial compounds, complex formation and alloy formation.
Important compounds
- K2Cr2O7: from chromite ore FeCr2O4; orange; strong oxidant in acid (Cr2O7 2- + 14H+ + 6e- gives 2Cr3+ + 7H2O, E0 = 1.33 V); chromate-dichromate interconvert with pH.
- KMnO4: from MnO2 via green manganate K2MnO4; purple, diamagnetic; strong oxidant whose product (Mn2+, MnO2 or MnO4 2-) depends on pH.
f-block
- Lanthanoids (Ce-Lu, 4f): chiefly +3; Ln3+ = 4f n; lanthanoid contraction from poor 4f shielding; Ce(IV) and Eu(II) are notable exceptions.
- Actinoids (Th-Lr, 5f): radioactive; wider range of oxidation states (5f, 6d, 7s comparable in energy); actinoid contraction greater than lanthanoid contraction.