A-Level Chemistry Edexcel 9CH0

be able to deduce the electronic configurations of atoms and ions of the d-block elements of period 4 (Sc–Zn), given the atomic number and charge (if any)

know that transition metals are d-block elements that form one or more stable ions with incompletely-filled d-orbitals

understand why transition metals show variable oxidation number

know what is meant by the term ‘ligand’

understand that dative (coordinate) bonding is involved in the formation of complex ions

know that a complex ion is a central metal ion surrounded by ligands

know that transition metals form coloured ions in solution

understand that the colour of aqueous ions, and other complex ions, results from the splitting of the energy levels of the d-orbitals by ligands

understand why there is a lack of colour in some aqueous ions and other complex ions

understand that colour changes in transition metal ions may arise as a result of changes in:

i) oxidation number ii) ligand iii) coordination number

understand the meaning of the term ‘coordination number’

understand why H₂O, OH⁻ and NH₃ act as monodentate ligands

understand why complexes with six-fold coordination have an octahedral shape, such as those formed by metal ions with H₂O, OH⁻ and NH₃ as ligands

know that transition metal ions may form tetrahedral complexes with relatively large ligands such as Cl⁻

know that square planar complexes are also formed by transition metal ions and that cis-platin is an example of such a complex

understand why cis-platin used in cancer treatment is supplied as a single isomer and not in a mixture with the trans form

be able to identify bidentate ligands, such as NH₂CH₂CH₂NH₂ and multidentate ligands, such as EDTA⁴⁻

know that haemoglobin is an iron(II) complex containing a multidentate ligand

The structure of the haem group will not be assessed.

know that a ligand exchange reaction occurs when an oxygen molecule bound to haemoglobin is replaced by a carbon monoxide molecule

know the colours of the oxidation states of vanadium (+5, +4, +3 and +2) in its compounds

understand redox reactions for the interconversion of the oxidation states of vanadium (+5, +4, +3 and +2), in terms of the relevant E^θ values

understand, in terms of the relevant E^θ values, that the dichromate (VI) ion, Cr₂O₇²⁻:

i) can be reduced to Cr³⁺ and Cr²⁺ ions using zinc in acidic conditions ii) can be produced by the oxidation of Cr³⁺ ions using hydrogen peroxide in alkaline conditions (followed by acidification)

know that the dichromate (VI) ion, Cr₂O₇²⁻, can be converted into chromate (VI) ions as a result of the equilibrium

2CrO₄²⁻ + 2H⁺ ⇌ Cr₂O₇²⁻ + H₂O

be able to record observations and write suitable equations for the reactions of Cr³⁺(aq), Fe²⁺(aq), Fe³⁺(aq), Co²⁺(aq) and Cu²⁺(aq) with aqueous sodium hydroxide and aqueous ammonia, including in excess

be able to write ionic equations to show the difference between ligand exchange and amphoteric behaviour for the reactions in (24) above

understand that ligand exchange, and an accompanying colour change, occurs in the formation of:

i) Cu(ΝΗ₃)₄(Η₂Ο)₂²⁺ from Cu(Η₂Ο)₆²⁺ via Cu(OH)₂(Η₂Ο)₄ ii) CuCl₄²⁻ from Cu(Η₂Ο)₆²⁺ iii) CoCl₄²⁻ from Co(Η₂Ο)₆²⁺

understand that the substitution of small, uncharged ligands (such as H₂O) by larger, charged ligands (such as Cl⁻) can lead to a change in coordination number

understand, in terms of the large positive increase in ΔS_system, that the substitution of a monodentate ligand by a bidentate or multidentate ligand leads to a more stable complex ion

know that transition metals and their compounds can act as heterogeneous and homogeneous catalysts

know that a heterogeneous catalyst is in a different phase from the reactants and that the reaction occurs at the surface of the catalyst

understand, in terms of oxidation number, how V₂O₅ acts as a catalyst in the contact process

understand how a catalytic converter decreases carbon monoxide and nitrogen monoxide emissions from internal combustion engines by:

i) adsorption of CO and NO molecules onto the surface of the catalyst ii) weakening of bonds and chemical reaction iii) desorption of CO₂ and N₂ product molecules from the surface of the catalyst

know that a homogeneous catalyst is in the same phase as the reactants and appreciate that the catalysed reaction will proceed via an intermediate species

understand the role of Fe²⁺ ions in catalysing the reaction between I⁻ and S₂O₈²⁻ ions

know the role of Mn²⁺ ions in autocatalysing the reaction between MnO₄⁻ and C₂O₄²⁻ ions

CORE PRACTICAL 12: The preparation of a transition metal complex