Chapter 4 — The d- and f-Block Elements
Iron in steel and haemoglobin, chromium in a polished tap, titanium in a hip joint, platinum in a catalytic converter: the metals in the middle of the periodic table build, colour and catalyse the modern world. Partly filled d and f orbitals explain all of it.
Walk through a hospital and count the transition metals. The surgical steel of a scalpel is iron hardened with chromium and nickel. A replacement hip joint is titanium, chosen because it is strong, light and ignored by the body. The red of blood comes from iron, the blue of a copper(II) sulphate test solution from copper, and an MRI scan is sharpened by a contrast agent built around gadolinium, a lanthanoid with seven unpaired electrons. In a chemistry laboratory the same block of the periodic table supplies the purple of potassium permanganate and the orange of potassium dichromate, two of the most useful oxidising agents in analysis.
Why are these elements so different from sodium or aluminium? They are all metals, but they show many oxidation states, form coloured and often magnetic compounds, bind ligands into complexes and speed up reactions as catalysts. Every one of these properties comes back to the same feature: an inner set of $d$ orbitals (or, for the lanthanoids and actinoids, $f$ orbitals) that is only partly filled. In this chapter you will build the electronic configurations, follow the trends across the first transition series and explain the exceptions, study the two famous oxidising agents, and see how the steady shrinking of the lanthanoids (the lanthanoid contraction) reaches forward to make zirconium and hafnium almost twins.
| Question | Key idea | Section |
|---|---|---|
| Why are Cr and Cu "exceptions"? | half-filled $3d^{5}$ and full $3d^{10}$ are extra stable | 4.1 |
| How magnetic is an ion? | $\mu=\sqrt{n(n+2)}\ \mathrm{BM}$, $n$ = unpaired electrons | 4.1 |
| Why are $\mathrm{Cu^{2+}}$ salts blue? | a $d$–$d$ transition absorbs the complementary colour | 4.1 |
| How much oxidant per mole? | $\mathrm{MnO_{4}^{-}}$ takes $5e^{-}$ in acid, $\mathrm{Cr_{2}O_{7}^{2-}}$ takes $6e^{-}$ | 4.2 |
| Why are Zr and Hf so alike? | the lanthanoid contraction cancels the expected increase in size | 4.3 |
- place the d- and f-block elements in the periodic table and write the electronic configurations of the 3d metals and their ions, including the exceptions Cr and Cu;
- explain the trends across the first transition series in metallic character, radii, ionisation enthalpies, enthalpies of atomisation, oxidation states and standard electrode potentials, and account for the irregular behaviour of Mn, Cu and Zn;
- count unpaired electrons, calculate spin-only magnetic moments, and explain the colour, complex formation, catalytic activity, interstitial compounds and alloys of transition metals;
- describe the preparation, structures and oxidising reactions of potassium dichromate and potassium permanganate in acidic, neutral and alkaline media, and balance their redox equations;
- write configurations and oxidation states of the lanthanoids and actinoids, explain the lanthanoid contraction and its consequences, compare the two series, and name important applications of d- and f-block elements.
Sections in this chapter
Transition Elements: Configuration and General Properties
Configurations, trends across the 3d series, oxidation states, $E^{\circ}$ values, magnetism, colour, catalysis, interstitial compounds and alloys.
Important Compounds: Potassium Dichromate and Potassium Permanganate
Oxides and oxoanions, the chromate–dichromate equilibrium, and the two oxidising agents in acidic, neutral and alkaline media.
Lanthanoids, Actinoids and Applications
4f and 5f configurations, the lanthanoid contraction and its consequences, oxidation states, and uses of d- and f-block elements.