Transition Metals
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15.1 Electronic configurations of Sc to Zn
From scandium to zinc, electrons fill the 3d sub-shell after 4s. Two exceptions: chromium is [Ar] 3d5 4s1 and copper is [Ar] 3d10 4s1, because a half-full or full d sub-shell is more stable.
When transition metals form ions, they lose the 4s electrons first. Fe is [Ar] 3d6 4s2; Fe2+ is [Ar] 3d6; Fe3+ is [Ar] 3d5.
Check yourself: Give the configuration of Cu2+.
[Ar] 3d9
15.2 What makes a transition metal, and variable oxidation numbers
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15.3 Ligands, dative bonds and complex ions
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15.4 Shapes of complex ions
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15.5 Bidentate and multidentate ligands; haemoglobin
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15.6 Why transition metal complexes are coloured
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15.7 Three causes of a colour change
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15.8 Vanadium: four colours, four oxidation numbers
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15.9 Chromium: dichromate(VI), chromium(III) and chromium(II)
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15.10 Reactions with sodium hydroxide and ammonia
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15.11 Ligand exchange and coordination number
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15.12 The chelate effect: an entropy explanation
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15.13 Heterogeneous catalysts
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15.14 Homogeneous catalysts and autocatalysis
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15.15 Core Practical 12: preparing a transition metal complex
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Extra worked questions
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All 8 worked solutions are free for members. The first one is open to everyone.
Two configurations
Give the electronic configuration of (a) a chromium atom and (b) an Fe3+ ion, using [Ar] for the inner electrons.
Try it first, then show the worked solution
| (a) | [Ar] 3d5 4s1 | 1 |
|---|---|---|
| (b) | Fe is [Ar] 3d6 4s2; lose 4s first, then one 3d: [Ar] 3d5 | 1 |
Answer: (a) [Ar] 3d5 4s1 (b) [Ar] 3d5
Examiner tip: 4s fills first and empties first. Write 3d before 4s to keep yourself straight.
Is it a transition metal?
Define a transition metal and use your definition to explain why scandium is not one.
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Shapes of four complexes
Give the shape of (a) [Cu(H2O)6]2+, (b) [CuCl4]2−, (c) [Pt(NH3)2Cl2] and (d) [Ag(NH3)2]+.
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The chelate effect with EDTA
Write an equation for EDTA4− replacing the water ligands in [Cu(H2O)6]2+, and explain why the reaction is feasible.
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Why the complex is blue
A copper(II) complex absorbs light of wavelength 600 nm. Explain why it appears coloured, and calculate the energy gap ΔE. h = 6.63 × 10−34 J s; c = 3.00 × 108 m s−1.
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Copper(II) with ammonia
Aqueous ammonia is added dropwise and then in excess to copper(II) sulfate solution. Describe what is seen and write an equation for each stage.
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Iron ions as a catalyst
Fe2+ ions catalyse the reaction S2O82− + 2I− → 2SO42− + I2. Explain why the uncatalysed reaction is slow, and write two equations to show how Fe2+ acts as a catalyst.
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Zinc and dichromate
Zinc is added to acidified potassium dichromate(VI) in a flask fitted with a valve that lets gas out but not air in. Describe the colour changes, giving the oxidation number of chromium at each stage, write the half-equation for the first stage, and explain why air is kept out.
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Video walkthroughs
Narrated walkthroughs of exam-style questions from this topic of the book, showing where each mark comes from. Try the question first, then watch. Captions are available in the player.
Why transition metal complexes are coloured
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Copper(II) ions with aqueous ammonia
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Yield of tetraamminecopper(II) sulfate
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Vanadium oxidation states and E values
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Purity of ammonium vanadate by titration
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