Chemistry study notes
Transition Elements
Connect d-electron configurations to physical trends, variable oxidation states, coloured complexes and catalysis.
A-Level 9476 (2026-2027)
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6 topicsIdentity and electron configurations
Identify transition elements and form their ions.
Physical properties and oxidation states
Explain the small physical trends and flexible electron accounting.
Three redox systems
Balance iron, manganate(VII) and dichromate(VI) reactions.
Ligands, complexes and observations
Follow copper colours, QA evidence and haemoglobin exchange.
Why complexes are coloured
Connect d-orbital orientation to visible-light absorption.
How transition-metal catalysts work
Follow a surface cycle and an electron-transfer cycle.
Scope
Learning outcomes
13. An Introduction to the Chemistry of Transition Elements. Use the outcome map to find the explanation for a particular syllabus requirement.
See the learning outcome map
13(a) Apply the transition-element definition.
- d-block atom with incomplete d subshell or cation with incomplete d subshell
- Sc and Cu inclusion; Zn distinction
13(b) Write first-row atom and ion configurations.
- Sc to Cu
- Cr and Cu neutral configurations
- Remove 4s before 3d on forming cations
- Cross-reference atomic structure 1(h)
13(c) Explain relatively small radius and first-ionisation-energy changes.
- Increasing nuclear charge
- Added 3d shielding
- Relatively invariant does not mean exactly constant
13(d) Compare transition-metal physical properties with calcium.
- Qualitative melting-point comparison
- Qualitative density comparison
- Metallic bonding and mass per volume
13(e) Explain variable oxidation states.
- Similar 3d/4s energies
- Fe and Cu examples
- Contrast with usual calcium +2
13(f) Suggest likely oxidation states from configuration.
- 4s and 3d electron participation
- Worked vanadium +2 and +5 deduction
- Formal oxidation number distinguished from a free aqueous ion
13(g) Explain the three specified redox systems.
- Fe3+/Fe2+
- MnO4-/Mn2+ in acid
- Cr2O7^2-/Cr3+ in acid
- Balanced half-equations, roles, observations and electron ratios
13(h) Predict redox likelihood from standard potentials.
- Reduction-potential comparison
- Positive Ecell standard thermodynamic criterion
- Do not multiply potentials by equation coefficients
- Cross-reference electrochemistry limitations
13(i) Define ligands and complexes using required examples.
- Cu(II) with water, ammonia and chloride
- Electron-pair donation and charge accounting
- Transition-metal complexes in official QA notes, including chromium hydroxo complex
Ligands donate electron pairs to a metal centreSeparate precipitation, ligand exchange and oxidation
13(j) Explain ligand exchange and associated colours.
- Cu aqua/ammine/chloro equilibria
- Initial copper hydroxide versus excess-ammonia complex
- CO/O2 exchange in haemoglobin
Ligands donate electron pairs to a metal centreSeparate precipitation, ligand exchange and oxidation
13(k) Explain octahedral d-orbital splitting.
- Five initially degenerate d orbitals
- Shapes and orientation relative to six axial ligands
- Higher pair and lower group of three
13(l) Explain colour through d-d transitions.
- Visible-light absorption across the splitting
- Observed versus absorbed colour
- Occupancy limits for d0/d10
- Ligand field-strength ranking not required
13(m) Explain catalytic action of transition elements and compounds.
- Surface adsorption, reaction and desorption
- Iron Haber and catalytic-converter examples
- Homogeneous Fe2+/Fe3+ peroxodisulfate/iodide cycle
- Catalyst regeneration and lower activation barrier; cross-reference 8(j)