Chemistry › Transition metals
Transition metals
Unit C14 · 5 lessons.
Zinc sits in the d block and is not a transition metal. The transition metals are the d-block elements that form at least one ion with a partly filled d subshell, and their chemistry follows from that: they form complexes with ligands, take up several shapes, swap ligands in substitution reactions, show colour, change oxidation state readily and catalyse reactions.
Colour is where answers go wrong. A complex is coloured because it absorbs light whose energy matches the gap between split d orbitals, so an electron is promoted; the colour seen is the light that is transmitted or reflected, the complement of what was absorbed. Saying the electron gives out the colour as it falls back is the answer the scheme rejects.
The papers that set it are AQA Papers 1 and 3, OCR A Papers 1 and 3, Edexcel Papers 1, 2 and 3 and Cambridge Paper 4.
Specification sections: AQA 3.2.5.1, 3.2.5.2, 3.2.5.3, 3.2.5.4, 3.2.5.5, 3.2.5.6 · OCR A 5.3.1 · Edexcel 15.1 to 15.35, 6.13, 9.8 · CAIE 28.1, 28.2, 28.4, 28.5, 28.3, 26.2
Notes
Illustrated notes for each topic in this unit, with worked examples and a checklist of objectives.
- Transition metal characteristics and complex formation
The definition of a transition metal and why scandium and zinc are excluded, the four characteristic properties, the electron configurations of titanium to copper and their ions, the shapes of the 3d orbitals, ligands, coordinate bonds, complexes, coordination number and counter-ions in salts, monodentate, bidentate and multidentate ligands including EDTA and the EDTA titration for water hardness, and haem with oxygen and carbon monoxide.
- Ligands, the shapes of complexes, isomerism and ligand substitution
Octahedral, tetrahedral, square planar and linear complexes, substitution of water by ammonia and by chloride ions with and without a change in coordination number, the equations and colours, cobalt(II) with sodium hydroxide, cis–trans and optical isomerism in complexes and the polarity of the isomers, the chelate effect explained by entropy, stability constants, and cisplatin as an anticancer drug given as a single isomer.
- Colour in transition metal complexes and colorimetry
Why transition metal ions are coloured, the splitting of d orbitals by ligands, ΔE = hν = hc/λ, complementary colours, the orbitals that rise and fall in an octahedral complex, ΔE in kJ mol⁻¹, the effect of oxidation state, ligand and coordination number on ΔE, why d⁰ and d¹⁰ ions are colourless and why manganate(VII) is coloured all the same, and colorimetry with a filter, a calibration curve and an unknown.
- Variable oxidation states: vanadium, chromium and manganate(VII) titrations
The four oxidation states of vanadium and their colours, reduction by zinc in acid and the electrode potentials that govern it, chromium(VI), (III) and (II), the effect of pH and ligand on redox stability including chromium(III) to chromate(VI) with hydrogen peroxide in alkali, iron(II) hydroxide oxidised by air, and Tollens' reagent, chromium(III) with sodium hydroxide and ammonia, and manganate(VII) titrations of iron(II) and ethanedioate with full calculations.
- Catalysis: heterogeneous, homogeneous and autocatalytic
Heterogeneous and homogeneous catalysts, adsorption, reaction and desorption on a surface, vanadium(V) oxide in the Contact process, iron in the Haber process, catalytic converters, support media and poisoning by lead and sulfur, nitrogen oxides catalysing the oxidation of sulfur dioxide in the air, Fe²⁺ catalysing the peroxodisulfate–iodide reaction and its reaction profile, and autocatalysis by Mn²⁺ in the manganate(VII)–ethanedioate reaction.
Key definitions for this unit
More for this topic