School / IB / CHEMISTRY HL / Structure 3: transition metals (HL) Exam-style + marking analysis
Structure 3: transition metals (HL) Transition metal electron configurations, complex ions, color, and catalysis.
Chemistry HL Structure 3: transition metals (HL)
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1 Write the full electron configuration of a chromium atom, and explain why it is 1s²2s²2p⁶3s²3p⁶3d⁵4s¹ rather than the configuration 1s²2s²2p⁶3s²3p⁶3d⁴4s² predicted by the simple aufbau order. Easy 3 marks No calculator + 2 Marking analysis: A learner attempts the following task: “Write the full electron configuration of a chromium atom, and explain why it is 1s²2s²2p⁶3s²3p⁶3d⁵4s¹ rather than the configuration 1s²2s²2p⁶3s²3p⁶3d⁴4s² predicted by the simple aufbau order.” Their response addresses only this point: “States the correct electron configuration: 1s²2s²2p⁶3s²3p⁶3d⁵4s¹.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 3 An iron atom has the electron configuration [Ar]3d⁶4s². Write the electron configuration of the Fe³⁺ ion, and state the number of unpaired electrons it contains. Easy 3 marks No calculator + 4 Marking analysis: A learner attempts the following task: “An iron atom has the electron configuration [Ar]3d⁶4s². Write the electron configuration of the Fe³⁺ ion, and state the number of unpaired electrons it contains.” Their response addresses only this point: “States that electrons are removed from the 4s subshell before the 3d subshell when forming a transition metal cation.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 5 Explain why zinc is not classified as a transition metal, even though it is a d-block element, while scandium is also excluded despite also being a d-block element. Easy 3 marks No calculator + 6 Marking analysis: A learner attempts the following task: “Explain why zinc is not classified as a transition metal, even though it is a d-block element, while scandium is also excluded despite also being a d-block element.” Their response addresses only this point: “States the definition: a transition metal must form at least one stable ion with a partially filled d subshell.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 7 Explain why transition metals commonly exhibit variable oxidation states, unlike most main group metals. Easy 3 marks No calculator + 8 Marking analysis: A learner attempts the following task: “Explain why transition metals commonly exhibit variable oxidation states, unlike most main group metals.” Their response addresses only this point: “States that the 3d and 4s subshells of transition metals have similar energies.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 9 Define the term 'ligand', and state the coordination number of copper in the complex ion [Cu(H₂O)₆]²⁺. Easy 2 marks No calculator + 10 Marking analysis: A learner attempts the following task: “Define the term 'ligand', and state the coordination number of copper in the complex ion [Cu(H₂O)₆]²⁺.” Their response addresses only this point: “Defines a ligand as a molecule or ion that donates a lone pair of electrons to a central metal ion, forming a coordinate (dative covalent) bond.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 2 marks No calculator + 11 Explain, in terms of d-orbital splitting, why solutions of transition metal complex ions, such as [Cu(H₂O)₆]²⁺, are typically colored. Medium 4 marks No calculator + 12 Marking analysis: A learner attempts the following task: “Explain, in terms of d-orbital splitting, why solutions of transition metal complex ions, such as [Cu(H₂O)₆]²⁺, are typically colored.” Their response addresses only this point: “States that in a free transition metal ion, the five d-orbitals are degenerate (equal in energy).” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 13 Explain why the Zn²⁺ ion and its complexes are colorless, unlike most other transition metal ions. Easy 3 marks No calculator + 14 Marking analysis: A learner attempts the following task: “Explain why the Zn²⁺ ion and its complexes are colorless, unlike most other transition metal ions.” Their response addresses only this point: “States that Zn²⁺ has a 3d¹⁰ electron configuration, a completely filled d subshell.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 15 When excess ammonia solution is added to a solution of [Cu(H₂O)₆]²⁺ (pale blue), a ligand substitution reaction occurs, forming [Cu(NH₃)₄(H₂O)₂]²⁺ (deep blue). Write the equation for this reaction, and explain why a color change is observed. Medium 4 marks No calculator + 16 Marking analysis: A learner attempts the following task: “When excess ammonia solution is added to a solution of [Cu(H₂O)₆]²⁺ (pale blue), a ligand substitution reaction occurs, forming [Cu(NH₃)₄(H₂O)₂]²⁺ (deep blue). Write the equation for this reaction, and explain why a color change is observed.” Their response addresses only this point: “Writes the equation: [Cu(H₂O)₆]²⁺ + 4NH₃ ⇌ [Cu(NH₃)₄(H₂O)₂]²⁺ + 4H₂O.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 17 Explain, with reference to variable oxidation states, how a transition metal ion such as Fe²⁺/Fe³⁺ can act as a homogeneous catalyst in a redox reaction between two species that would otherwise react very slowly. Medium 4 marks No calculator + 18 Marking analysis: A learner attempts the following task: “Explain, with reference to variable oxidation states, how a transition metal ion such as Fe²⁺/Fe³⁺ can act as a homogeneous catalyst in a redox reaction between two species that would otherwise react very slowly.” Their response addresses only this point: “States that the transition metal ion provides an alternative reaction pathway with a lower activation energy than the direct, uncatalyzed reaction.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks No calculator + 19 Determine the oxidation state of cobalt in the complex ion [Co(NH₃)₅Cl]²⁺. Medium 4 marks Calculator + 20 Marking analysis: A learner attempts the following task: “Determine the oxidation state of cobalt in the complex ion [Co(NH₃)₅Cl]²⁺.” Their response addresses only this point: “States that ammonia, NH₃, is a neutral ligand, contributing 0 to the overall charge.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Medium 4 marks Calculator + 21 Explain why the same transition metal ion, such as Fe²⁺, can form complexes of different colors depending on the ligand attached, referring to the spectrochemical series. Easy 3 marks No calculator + 22 Marking analysis: A learner attempts the following task: “Explain why the same transition metal ion, such as Fe²⁺, can form complexes of different colors depending on the ligand attached, referring to the spectrochemical series.” Their response addresses only this point: “States that different ligands produce different strengths of crystal field splitting, as ranked by the spectrochemical series.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 23 State the shape of the complex ion [CuCl₄]²⁻, and explain why it adopts a different shape from the six-coordinate [Cu(H₂O)₆]²⁺. Easy 3 marks No calculator + 24 Marking analysis: A learner attempts the following task: “State the shape of the complex ion [CuCl₄]²⁻, and explain why it adopts a different shape from the six-coordinate [Cu(H₂O)₆]²⁺.” Their response addresses only this point: “States that [CuCl₄]²⁻ has a tetrahedral shape.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 25 The square planar complex [Pt(NH₃)₂Cl₂] exists as two distinct geometric isomers, cis and trans. Describe the difference between the cis and trans arrangements. Easy 3 marks No calculator + 26 Marking analysis: A learner attempts the following task: “The square planar complex [Pt(NH₃)₂Cl₂] exists as two distinct geometric isomers, cis and trans. Describe the difference between the cis and trans arrangements.” Their response addresses only this point: “Describes the cis isomer as having the two identical ligands (the two NH₃ groups, or equivalently the two Cl ligands) positioned adjacent to each other, at 90° to one another.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 27 The octahedral complex [Ni(en)₃]²⁺ (where 'en' is the bidentate ligand ethylenediamine) can exist as non-superimposable mirror images. Explain why this complex is chiral (optically active). Easy 3 marks No calculator + 28 Marking analysis: A learner attempts the following task: “The octahedral complex [Ni(en)₃]²⁺ (where 'en' is the bidentate ligand ethylenediamine) can exist as non-superimposable mirror images. Explain why this complex is chiral (optically active).” Their response addresses only this point: “States that the complex has no plane of symmetry, due to the way the three bidentate ligands wrap around the central metal ion in a propeller-like arrangement.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 29 Give the systematic (IUPAC) name of the complex ion [Cu(NH₃)₄(H₂O)₂]²⁺. Easy 3 marks No calculator + 30 Marking analysis: A learner attempts the following task: “Give the systematic (IUPAC) name of the complex ion [Cu(NH₃)₄(H₂O)₂]²⁺.” Their response addresses only this point: “Names the ammonia ligands using the prefix 'tetraammine' (4 ammonia ligands).” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + 31 State the number of unpaired electrons in the Fe³⁺ ion ([Ar]3d⁵), and explain how this relates to the magnetic behaviour of its compounds. Easy 2 marks No calculator + 32 Marking analysis: A learner attempts the following task: “State the number of unpaired electrons in the Fe³⁺ ion ([Ar]3d⁵), and explain how this relates to the magnetic behaviour of its compounds.” Their response addresses only this point: “States that by Hund's rule, the five electrons in the 3d⁵ configuration occupy all five d-orbitals singly before any pairing occurs, giving 5 unpaired electrons.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 2 marks No calculator + 33 Describe the general trend in first ionization energy across the first row of transition metals (Sc to Zn), and explain why this trend is much less pronounced than the trend across a main group period. Easy 3 marks No calculator + 34 Marking analysis: A learner attempts the following task: “Describe the general trend in first ionization energy across the first row of transition metals (Sc to Zn), and explain why this trend is much less pronounced than the trend across a main group period.” Their response addresses only this point: “Describes the general trend as a relatively small, somewhat irregular increase in first ionization energy from Sc to Zn, rather than a large, steady increase.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks. Marking analysis Easy 3 marks No calculator + Self-assessed 0 / 0
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