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The d- and f-Block Elements

Electronic configurations, oxidation states and magnetic moments across the series, the lanthanoid contraction, and the chemistry of dichromate and permanganate.

Questions in the bank
214
q/paper in 2025–26
1.45
Calculation
28%
Notes pages
8

Strand: Structure and recall

When you’ll see it

A 3d, 4f or 5f ion's configuration, oxidation state, colour or magnetic moment; an E° clue to an oxidant or reductant; permanganate, dichromate or a transition-metal oxide; or a salt-analysis test for a cation.

How this chapter is tested

A large share of the numeric answers are spin-only moments. Find the ion the clue points to, take its 4s electrons off first, count the unpaired d or f electrons, and use √(n(n+2)) BM. The same count decides colour: d⁰ and d¹⁰ ions are colourless and diamagnetic, and permanganate and dichromate owe their colour to charge transfer instead.

The rest is recall with a few rules behind it. A higher oxidation state makes an oxide more acidic and more covalent. Down a d-block group the higher state grows more stable, the opposite of the p-block. The medium decides permanganate's product: Mn²⁺ in acid (five electrons), MnO₂ in neutral or faintly alkaline solution (three). Chromium stays +6 from chromate through dichromate to CrO₂Cl₂ and CrO₅.

The lanthanoids reduce to one count: Ln³⁺ is 4fⁿ with n = Z − 57, so the +4 ions near 4f⁰ or 4f⁷ (Ce, Tb) oxidise and the +2 ions (Eu, Yb) reduce. Qualitative analysis is three tables (group reagents, confirmatory colours, borax beads), where one swapped pair costs the mark.

The sub-skills

The distinct skills inside the chapter, in the order to learn them.

  • Configurations and general properties

    Cr is 3d⁵4s¹ and Cu 3d¹⁰4s¹; ions lose 4s first; Cr's second ionisation enthalpy beats Mn's but its third does not; atomisation enthalpy peaks at V, dips at Mn and is lowest at Zn.

  • Oxidation states and E°

    Mn shows +2 to +7 and Sc only +3; oxygen holds higher states than fluorine; Cu has the only positive M²⁺/M value; Mn³⁺ and Co³⁺ oxidise, Cr²⁺ reduces; Cu⁺ disproportionates in water.

  • Magnetic moment and colour

    μ = √(n(n+2)) BM gives 1.73, 2.83, 3.87, 4.90, 5.92 for n = 1 to 5; past d⁵ use n = 10 − x; d⁰ and d¹⁰ are colourless; V²⁺, Cr³⁺ and Mn³⁺ are all violet.

  • Transition-metal oxides

    Higher state, more acidic: CrO basic, Cr₂O₃ amphoteric, CrO₃ acidic; V₂O₅ amphoteric; Mn₂O₇ is two corner-sharing tetrahedra, covalent, with no Mn–Mn bond; Fe₃O₄ and Mn₃O₄ are mixed oxides.

  • Dichromate and chromium

    Chromite to Na₂CrO₄ to K₂Cr₂O₇; chromate against dichromate is a pH change at +6; acidified dichromate takes six electrons; the CrO₂Cl₂ test for chloride ends in blue CrO₅, +6 with two peroxo groups.

  • Permanganate and manganese

    MnO₂ fused with KOH gives green K₂MnO₄ (+6, d¹, 1.73 BM), which disproportionates to MnO₄⁻ and MnO₂; acid permanganate takes five electrons, neutral three; titrate in H₂SO₄, never HCl.

  • Lanthanoids and actinoids

    Ln³⁺ is 4fⁿ with n = Z − 57; Ce⁴⁺ and Tb⁴⁺ oxidise, Eu²⁺ and Yb²⁺ reduce; Gd³⁺ gives 7.94 BM; actinoids use 5f in bonding, show more states and a larger contraction; Cm has eight unpaired electrons.

  • Qualitative analysis

    Group reagents run from dilute HCl to (NH₄)₂CO₃; ferrocyanide gives chocolate-brown with Cu²⁺ and Prussian blue with Fe³⁺; dmg gives red with Ni²⁺; Nessler's gives brown with NH₄⁺; iron in the brown ring is +1.

Traps to expect

Distractor shapes this chapter reuses. The Traps page covers the ones that cut across chapters.

  • 3d emptied before 4s

    Mn²⁺ is 3d⁵ with 5.92 BM. Writing it as 3d³4s² gives 3.87 BM, and that value is usually an option.

  • Colour taken for paramagnetism

    Permanganate is deep purple, but Mn(VII) is d⁰ and diamagnetic. Dichromate and chromate are the same: coloured by charge transfer.

  • Manganate and permanganate swapped

    MnO₄²⁻ is green, +6 and paramagnetic; MnO₄⁻ is purple, +7 and diamagnetic. Peroxodisulphate takes Mn²⁺ all the way to permanganate.

  • Peroxo oxygens counted as −2

    CrO₅ is +6, not +10, and chromate to dichromate is not a redox change. Give every peroxo oxygen −1.

  • The p-block trend carried over

    Down a d-block group the higher state grows more stable, so Cr(VI) is less stable than Mo(VI), and CrO₃ is the strongest oxidant of the three trioxides.

Learn it before you drill it

This chapter has full teaching notes — foundations, worked examples, self-checks and a mastery check for each page. Read the notes once, then drill page by page below.

The d- and f-Block Elements notes

Drill every The d- and f-Block Elements question

214 questions from the bank, across 8 subtopics.

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The 8 subtopics, in teaching order.

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