Define a transition metal.
[1 mark]
Total for this question: 1
Chemistry
Transition metals
AQA 3.2.5
A-level Chemistry (7405) · exam-style practice, examiner-report intelligence and the tools that drill it.
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The topic on one screen
- A transition metal is a d-block element that forms at least one stable ion with a partially filled (incomplete) d-subshell.
- A ligand donates a lone pair of electrons to the metal ion, forming a coordinate (dative covalent) bond; the metal + ligands = a complex.
- Ligands can be monodentate (e.g. H2O, NH3, Cl-), bidentate (e.g. ethanedioate, en) or multidentate (e.g. EDTA).
- Common shapes are set by coordination number: octahedral has 6 coordinate bonds, tetrahedral or square planar has 4, and linear has 2. The number of ligand particles can be smaller when ligands are bidentate or multidentate.
- Colour comes from d-d transitions: d orbitals split, electrons absorb visible light to jump, and the complementary colour is seen. Change the ligand, coordination number or oxidation state and the colour changes.
- Catalysis: variable oxidation states let transition metals accept and donate electrons (homogeneous), or their surface adsorbs reactants (heterogeneous).
Where students actually lose marks
Defining a transition metal COMPLEX, several answers didn't refer to an atom or ion, or gave the definition of a transition metal instead. Be precise about what the term is asking for.
June 2023 Paper 1 examiner report (Q01.1)
The chelate effect was poorly recalled: it is driven by entropy (more particles released than taken in), not by 'stronger bonds forming'.
June 2024 Paper 1 examiner report (Q03.2)
That variable oxidation states matter for transition-metal catalysis is usually known, but few stressed it in their answers. Say it explicitly.
June 2024 Paper 1 examiner report (Q03.3)
Try it — exam-style
Easy
ORIGINAL
Medium
ORIGINAL · after June 2023 Paper 1 Q01.1
Explain what is meant by a ligand and state the type of bond it forms with a transition metal ion.
[2 marks]
Total for this question: 2
Hard
ORIGINAL · after June 2024 Paper 1 Q03.2
When six water ligands in [Cu(H2O)6]2+ are replaced by three bidentate ethanedioate ligands, the complex becomes more stable. Explain this in terms of entropy.
[2 marks]
Total for this question: 2
Medium
ORIGINAL · after June 2024 Paper 1 Q03.3
Explain why transition metals and their compounds are often good catalysts.
[2 marks]
Total for this question: 2
Medium
ORIGINAL
Explain why aqueous transition metal ions are coloured, and state one change that would change the colour.
[3 marks]
Total for this question: 3
Questions are written in the style of past AQA papers (source shown on each) — never copied from them.
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