Chemistry SL

1. 1.

   State how elements are arranged in the modern periodic table, and how this arrangement relates to electron configuration.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that elements are arranged in order of increasing atomic number. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that elements in the same group (vertical column) have the same number of electrons in their outer shell. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that elements in the same period (horizontal row) have the same number of occupied electron shells. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The periodic table's structure directly reflects electron configuration — group number relates to outer-shell electrons, period number relates to the highest occupied shell.

   Marking points

   • States that elements are arranged in order of increasing atomic number.
   • States that elements in the same group (vertical column) have the same number of electrons in their outer shell.
   • States that elements in the same period (horizontal row) have the same number of occupied electron shells.

   Examiner tip: The periodic table's structure directly reflects electron configuration — group number relates to outer-shell electrons, period number relates to the highest occupied shell.

2. 2.

   Marking analysis: A learner attempts the following task: “State how elements are arranged in the modern periodic table, and how this arrangement relates to electron configuration.” Their response addresses only this point: “States that elements are arranged in order of increasing atomic number.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
   2. Requirement 1: Recognises credit for the stated point: States that elements are arranged in order of increasing atomic number. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   3. Requirement 2: Identifies the missing requirement: States that elements in the same group (vertical column) have the same number of electrons in their outer shell. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   4. Requirement 3: Identifies the missing requirement: States that elements in the same period (horizontal row) have the same number of occupied electron shells. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

   Marking points

   • Recognises credit for the stated point: States that elements are arranged in order of increasing atomic number.
   • Identifies the missing requirement: States that elements in the same group (vertical column) have the same number of electrons in their outer shell.
   • Identifies the missing requirement: States that elements in the same period (horizontal row) have the same number of occupied electron shells.

   Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

3. 3.

   Explain why the first ionization energies generally increase across period 3 (from sodium to argon), despite some small irregularities.

   [4 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that nuclear charge increases across the period as protons are added. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that shielding remains roughly constant, since electrons are added to the same principal energy level. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that the increasing nuclear charge with roughly constant shielding results in a stronger effective nuclear attraction on the outer electrons. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Develop this part of the answer: States that this stronger attraction, and the resulting smaller atomic radius, require more energy to remove an outer electron, so ionization energy generally increases. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The general period trend is explained by increasing nuclear charge with roughly constant shielding; small dips require a separate sub-shell explanation, not this general trend.

   Marking points

   • States that nuclear charge increases across the period as protons are added.
   • States that shielding remains roughly constant, since electrons are added to the same principal energy level.
   • States that the increasing nuclear charge with roughly constant shielding results in a stronger effective nuclear attraction on the outer electrons.
   • States that this stronger attraction, and the resulting smaller atomic radius, require more energy to remove an outer electron, so ionization energy generally increases.

   Examiner tip: The general period trend is explained by increasing nuclear charge with roughly constant shielding; small dips require a separate sub-shell explanation, not this general trend.

4. 4.

   Marking analysis: A learner attempts the following task: “Explain why the first ionization energies generally increase across period 3 (from sodium to argon), despite some small irregularities.” Their response addresses only this point: “States that nuclear charge increases across the period as protons are added.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.

   [4 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
   2. Requirement 1: Recognises credit for the stated point: States that nuclear charge increases across the period as protons are added. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   3. Requirement 2: Identifies the missing requirement: States that shielding remains roughly constant, since electrons are added to the same principal energy level. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   4. Requirement 3: Identifies the missing requirement: States that the increasing nuclear charge with roughly constant shielding results in a stronger effective nuclear attraction on the outer electrons. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   5. Requirement 4: Identifies the missing requirement: States that this stronger attraction, and the resulting smaller atomic radius, require more energy to remove an outer electron, so ionization energy generally increases. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

   Marking points

   • Recognises credit for the stated point: States that nuclear charge increases across the period as protons are added.
   • Identifies the missing requirement: States that shielding remains roughly constant, since electrons are added to the same principal energy level.
   • Identifies the missing requirement: States that the increasing nuclear charge with roughly constant shielding results in a stronger effective nuclear attraction on the outer electrons.
   • Identifies the missing requirement: States that this stronger attraction, and the resulting smaller atomic radius, require more energy to remove an outer electron, so ionization energy generally increases.

   Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

5. 5.

   Explain why atomic radius decreases across a period but increases down a group.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that across a period, nuclear charge increases while shielding stays roughly constant, so the increased effective nuclear attraction pulls the outer electrons closer, decreasing atomic radius. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that down a group, an additional electron shell is added at each step. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that this additional shell places the outer electrons further from the nucleus, and increased shielding from inner shells also reduces the effective nuclear attraction, so atomic radius increases despite the larger nuclear charge. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Two competing factors (nuclear charge and shielding/number of shells) explain both periodic trends — identify which factor dominates in each case.

   Marking points

   • States that across a period, nuclear charge increases while shielding stays roughly constant, so the increased effective nuclear attraction pulls the outer electrons closer, decreasing atomic radius.
   • States that down a group, an additional electron shell is added at each step.
   • States that this additional shell places the outer electrons further from the nucleus, and increased shielding from inner shells also reduces the effective nuclear attraction, so atomic radius increases despite the larger nuclear charge.

   Examiner tip: Two competing factors (nuclear charge and shielding/number of shells) explain both periodic trends — identify which factor dominates in each case.

6. 6.

   Marking analysis: A learner attempts the following task: “Explain why atomic radius decreases across a period but increases down a group.” Their response addresses only this point: “States that across a period, nuclear charge increases while shielding stays roughly constant, so the increased effective nuclear attraction pulls the outer electrons closer, decreasing atomic radius.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
   2. Requirement 1: Recognises credit for the stated point: States that across a period, nuclear charge increases while shielding stays roughly constant, so the increased effective nuclear attraction pulls the outer electrons closer, decreasing atomic radius. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   3. Requirement 2: Identifies the missing requirement: States that down a group, an additional electron shell is added at each step. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   4. Requirement 3: Identifies the missing requirement: States that this additional shell places the outer electrons further from the nucleus, and increased shielding from inner shells also reduces the effective nuclear attraction, so atomic radius increases despite the larger nuclear charge. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

   Marking points

   • Recognises credit for the stated point: States that across a period, nuclear charge increases while shielding stays roughly constant, so the increased effective nuclear attraction pulls the outer electrons closer, decreasing atomic radius.
   • Identifies the missing requirement: States that down a group, an additional electron shell is added at each step.
   • Identifies the missing requirement: States that this additional shell places the outer electrons further from the nucleus, and increased shielding from inner shells also reduces the effective nuclear attraction, so atomic radius increases despite the larger nuclear charge.

   Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

7. 7.

   Describe the general trend in electronegativity across a period and down a group, and state which element is the most electronegative.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that electronegativity generally increases across a period. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that electronegativity generally decreases down a group. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that fluorine is the most electronegative element. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Electronegativity trends mirror the trends in nuclear attraction on bonding electrons — the same reasoning (nuclear charge vs. shielding/distance) applies as for atomic radius and ionization energy.

   Marking points

   • States that electronegativity generally increases across a period.
   • States that electronegativity generally decreases down a group.
   • States that fluorine is the most electronegative element.

   Examiner tip: Electronegativity trends mirror the trends in nuclear attraction on bonding electrons — the same reasoning (nuclear charge vs. shielding/distance) applies as for atomic radius and ionization energy.

8. 8.

   Marking analysis: A learner attempts the following task: “Describe the general trend in electronegativity across a period and down a group, and state which element is the most electronegative.” Their response addresses only this point: “States that electronegativity generally increases across a period.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

   [3 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
   2. Requirement 1: Recognises credit for the stated point: States that electronegativity generally increases across a period. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   3. Requirement 2: Identifies the missing requirement: States that electronegativity generally decreases down a group. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   4. Requirement 3: Identifies the missing requirement: States that fluorine is the most electronegative element. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
   5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

   Marking points

   • Recognises credit for the stated point: States that electronegativity generally increases across a period.
   • Identifies the missing requirement: States that electronegativity generally decreases down a group.
   • Identifies the missing requirement: States that fluorine is the most electronegative element.

   Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

9. 9.

   Ethanol and methoxymethane have the same molecular formula, C₂H₆O. Explain why ethanol has the higher boiling point.

   [4 marks] · no calculator

   Answer explanation

   Draft walkthroughs are based on marking guidance, not independently verified derivations.

   1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
   2. Develop this part of the answer: States that ethanol has an −OH functional group, allowing its molecules to form hydrogen bonds with each other. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   3. Develop this part of the answer: States that methoxymethane has an ether functional group (C−O−C), with no hydrogen directly bonded to a highly electronegative atom, so it relies only on weaker dipole-dipole and van der Waals forces. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   4. Develop this part of the answer: States that hydrogen bonds are stronger intermolecular forces than dipole-dipole or van der Waals forces. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   5. Develop this part of the answer: States that more energy is therefore required to separate ethanol molecules, giving it a higher boiling point. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
   6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Identifying the functional group present is the key first step in comparing intermolecular forces (and hence physical properties) between isomers.

   Marking points

   • States that ethanol has an −OH functional group, allowing its molecules to form hydrogen bonds with each other.
   • States that methoxymethane has an ether functional group (C−O−C), with no hydrogen directly bonded to a highly electronegative atom, so it relies only on weaker dipole-dipole and van der Waals forces.
   • States that hydrogen bonds are stronger intermolecular forces than dipole-dipole or van der Waals forces.
   • States that more energy is therefore required to separate ethanol molecules, giving it a higher boiling point.

   Examiner tip: Identifying the functional group present is the key first step in comparing intermolecular forces (and hence physical properties) between isomers.

10. 10.

    Marking analysis: A learner attempts the following task: “Ethanol and methoxymethane have the same molecular formula, C₂H₆O. Explain why ethanol has the higher boiling point.” Their response addresses only this point: “States that ethanol has an −OH functional group, allowing its molecules to form hydrogen bonds with each other.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that ethanol has an −OH functional group, allowing its molecules to form hydrogen bonds with each other. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that methoxymethane has an ether functional group (C−O−C), with no hydrogen directly bonded to a highly electronegative atom, so it relies only on weaker dipole-dipole and van der Waals forces. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: States that hydrogen bonds are stronger intermolecular forces than dipole-dipole or van der Waals forces. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Requirement 4: Identifies the missing requirement: States that more energy is therefore required to separate ethanol molecules, giving it a higher boiling point. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that ethanol has an −OH functional group, allowing its molecules to form hydrogen bonds with each other.
    • Identifies the missing requirement: States that methoxymethane has an ether functional group (C−O−C), with no hydrogen directly bonded to a highly electronegative atom, so it relies only on weaker dipole-dipole and van der Waals forces.
    • Identifies the missing requirement: States that hydrogen bonds are stronger intermolecular forces than dipole-dipole or van der Waals forces.
    • Identifies the missing requirement: States that more energy is therefore required to separate ethanol molecules, giving it a higher boiling point.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

11. 11.

    Propane, C₃H₈, is a member of the alkane homologous series. State the general formula of the alkanes and use it to write the molecular formula of the alkane with 6 carbon atoms.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Work through this mathematical step: States the general formula CₙH₂ₙ₊₂. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    3. Work through this mathematical step: Substitutes n = 6. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    4. Work through this mathematical step: Writes the molecular formula C₆H₁₄. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Substitute the carbon number directly into the general formula rather than counting atoms from a drawn structure.

    Marking points

    • States the general formula CₙH₂ₙ₊₂.
    • Substitutes n = 6.
    • Writes the molecular formula C₆H₁₄.

    Examiner tip: Substitute the carbon number directly into the general formula rather than counting atoms from a drawn structure.

12. 12.

    Marking analysis: A learner attempts the following task: “Propane, C₃H₈, is a member of the alkane homologous series. State the general formula of the alkanes and use it to write the molecular formula of the alkane with 6 carbon atoms.” Their response addresses only this point: “States the general formula CₙH₂ₙ₊₂.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States the general formula CₙH₂ₙ₊₂. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: Substitutes n = 6. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: Writes the molecular formula C₆H₁₄. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States the general formula CₙH₂ₙ₊₂.
    • Identifies the missing requirement: Substitutes n = 6.
    • Identifies the missing requirement: Writes the molecular formula C₆H₁₄.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

13. 13.

    Identify the functional group present in a carboxylic acid, and state the general formula of the homologous series.

    [2 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: Identifies the carboxyl functional group, −COOH. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Work through this mathematical step: States the general formula CₙH₂ₙ₊₁COOH (or equivalent form). Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Identifying the functional group present in an unknown structure is the first step in classifying it into the correct homologous series and predicting its chemical behaviour.

    Marking points

    • Identifies the carboxyl functional group, −COOH.
    • States the general formula CₙH₂ₙ₊₁COOH (or equivalent form).

    Examiner tip: Identifying the functional group present in an unknown structure is the first step in classifying it into the correct homologous series and predicting its chemical behaviour.

14. 14.

    Marking analysis: A learner attempts the following task: “Identify the functional group present in a carboxylic acid, and state the general formula of the homologous series.” Their response addresses only this point: “Identifies the carboxyl functional group, −COOH.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [2 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: Identifies the carboxyl functional group, −COOH. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States the general formula CₙH₂ₙ₊₁COOH (or equivalent form). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: Identifies the carboxyl functional group, −COOH.
    • Identifies the missing requirement: States the general formula CₙH₂ₙ₊₁COOH (or equivalent form).

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

15. 15.

    Explain how infrared (IR) spectroscopy can be used to identify the presence of a carbonyl group (C=O) in an organic molecule.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that different bonds absorb infrared radiation at characteristic frequencies (wavenumbers), causing them to vibrate. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Work through this mathematical step: States that a C=O bond has a characteristic, easily identifiable strong absorption in a specific wavenumber region of the IR spectrum. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    4. Develop this part of the answer: States that observing a strong absorption peak in this specific region provides evidence for the presence of a carbonyl group. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Each type of bond has its own characteristic absorption region, so identifying peaks allows functional groups to be deduced without solving the full structure — this links directly to classifying matter by functional group.

    Marking points

    • States that different bonds absorb infrared radiation at characteristic frequencies (wavenumbers), causing them to vibrate.
    • States that a C=O bond has a characteristic, easily identifiable strong absorption in a specific wavenumber region of the IR spectrum.
    • States that observing a strong absorption peak in this specific region provides evidence for the presence of a carbonyl group.

    Examiner tip: Each type of bond has its own characteristic absorption region, so identifying peaks allows functional groups to be deduced without solving the full structure — this links directly to classifying matter by functional group.

16. 16.

    Marking analysis: A learner attempts the following task: “Explain how infrared (IR) spectroscopy can be used to identify the presence of a carbonyl group (C=O) in an organic molecule.” Their response addresses only this point: “States that different bonds absorb infrared radiation at characteristic frequencies (wavenumbers), causing them to vibrate.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that different bonds absorb infrared radiation at characteristic frequencies (wavenumbers), causing them to vibrate. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that a C=O bond has a characteristic, easily identifiable strong absorption in a specific wavenumber region of the IR spectrum. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: States that observing a strong absorption peak in this specific region provides evidence for the presence of a carbonyl group. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that different bonds absorb infrared radiation at characteristic frequencies (wavenumbers), causing them to vibrate.
    • Identifies the missing requirement: States that a C=O bond has a characteristic, easily identifiable strong absorption in a specific wavenumber region of the IR spectrum.
    • Identifies the missing requirement: States that observing a strong absorption peak in this specific region provides evidence for the presence of a carbonyl group.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

17. 17.

    A mass spectrum of an organic compound shows a molecular ion peak at m/z = 46. Suggest the molecular formula of a compound consistent with this molecular mass, given it contains only carbon, hydrogen and oxygen.

    [3 marks]

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that the molecular ion peak (M+) gives the relative molecular mass of the compound directly. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Work through this mathematical step: Tests a reasonable formula, e.g. C2H6O (Mr = 46). Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    4. Work through this mathematical step: Confirms the formula mass matches: 2(12.0) + 6(1.0) + 16.0 = 46. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The molecular ion peak (the highest-mass peak, ignoring isotope peaks) directly gives the relative molecular mass, a key first step in identifying an unknown's classification.

    Marking points

    • States that the molecular ion peak (M+) gives the relative molecular mass of the compound directly.
    • Tests a reasonable formula, e.g. C2H6O (Mr = 46).
    • Confirms the formula mass matches: 2(12.0) + 6(1.0) + 16.0 = 46.

    Examiner tip: The molecular ion peak (the highest-mass peak, ignoring isotope peaks) directly gives the relative molecular mass, a key first step in identifying an unknown's classification.

18. 18.

    Marking analysis: A learner attempts the following task: “A mass spectrum of an organic compound shows a molecular ion peak at m/z = 46. Suggest the molecular formula of a compound consistent with this molecular mass, given it contains only carbon, hydrogen and oxygen.” Their response addresses only this point: “States that the molecular ion peak (M+) gives the relative molecular mass of the compound directly.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [3 marks]

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that the molecular ion peak (M+) gives the relative molecular mass of the compound directly. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: Tests a reasonable formula, e.g. C2H6O (Mr = 46). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: Confirms the formula mass matches: 2(12.0) + 6(1.0) + 16.0 = 46. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that the molecular ion peak (M+) gives the relative molecular mass of the compound directly.
    • Identifies the missing requirement: Tests a reasonable formula, e.g. C2H6O (Mr = 46).
    • Identifies the missing requirement: Confirms the formula mass matches: 2(12.0) + 6(1.0) + 16.0 = 46.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

19. 19.

    Distinguish between a saturated and an unsaturated hydrocarbon, and describe a simple chemical test to distinguish between them.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that a saturated hydrocarbon contains only single carbon-carbon bonds, e.g. alkanes. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that an unsaturated hydrocarbon contains at least one carbon-carbon double (or triple) bond, e.g. alkenes. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: Describes adding bromine water: it stays orange/brown with a saturated hydrocarbon, but decolourises with an unsaturated one. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The bromine water test distinguishes saturation directly: no colour change means saturated, decolourisation means unsaturated — this classification test is a core Structure 3 skill.

    Marking points

    • States that a saturated hydrocarbon contains only single carbon-carbon bonds, e.g. alkanes.
    • States that an unsaturated hydrocarbon contains at least one carbon-carbon double (or triple) bond, e.g. alkenes.
    • Describes adding bromine water: it stays orange/brown with a saturated hydrocarbon, but decolourises with an unsaturated one.

    Examiner tip: The bromine water test distinguishes saturation directly: no colour change means saturated, decolourisation means unsaturated — this classification test is a core Structure 3 skill.

20. 20.

    Marking analysis: A learner attempts the following task: “Distinguish between a saturated and an unsaturated hydrocarbon, and describe a simple chemical test to distinguish between them.” Their response addresses only this point: “States that a saturated hydrocarbon contains only single carbon-carbon bonds, e.g. alkanes.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that a saturated hydrocarbon contains only single carbon-carbon bonds, e.g. alkanes. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that an unsaturated hydrocarbon contains at least one carbon-carbon double (or triple) bond, e.g. alkenes. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: Describes adding bromine water: it stays orange/brown with a saturated hydrocarbon, but decolourises with an unsaturated one. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that a saturated hydrocarbon contains only single carbon-carbon bonds, e.g. alkanes.
    • Identifies the missing requirement: States that an unsaturated hydrocarbon contains at least one carbon-carbon double (or triple) bond, e.g. alkenes.
    • Identifies the missing requirement: Describes adding bromine water: it stays orange/brown with a saturated hydrocarbon, but decolourises with an unsaturated one.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

21. 21.

    State the general position of metals, non-metals and metalloids in the periodic table, and state one physical property that generally distinguishes metals from non-metals.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that metals are found on the left and towards the bottom of the periodic table, while non-metals are found on the right and towards the top. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that metalloids lie along the diagonal 'staircase' boundary between metals and non-metals, showing intermediate properties of both. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States a valid distinguishing property, e.g. metals are generally good conductors of electricity and heat, malleable and ductile, while non-metals are generally poor conductors and brittle when solid. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The metal-nonmetal 'staircase' line runs diagonally from boron down to astatine on the periodic table, with metalloids (e.g. silicon, germanium) sitting directly along it.

    Marking points

    • States that metals are found on the left and towards the bottom of the periodic table, while non-metals are found on the right and towards the top.
    • States that metalloids lie along the diagonal 'staircase' boundary between metals and non-metals, showing intermediate properties of both.
    • States a valid distinguishing property, e.g. metals are generally good conductors of electricity and heat, malleable and ductile, while non-metals are generally poor conductors and brittle when solid.

    Examiner tip: The metal-nonmetal 'staircase' line runs diagonally from boron down to astatine on the periodic table, with metalloids (e.g. silicon, germanium) sitting directly along it.

22. 22.

    Marking analysis: A learner attempts the following task: “State the general position of metals, non-metals and metalloids in the periodic table, and state one physical property that generally distinguishes metals from non-metals.” Their response addresses only this point: “States that metals are found on the left and towards the bottom of the periodic table, while non-metals are found on the right and towards the top.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that metals are found on the left and towards the bottom of the periodic table, while non-metals are found on the right and towards the top. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that metalloids lie along the diagonal 'staircase' boundary between metals and non-metals, showing intermediate properties of both. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: States a valid distinguishing property, e.g. metals are generally good conductors of electricity and heat, malleable and ductile, while non-metals are generally poor conductors and brittle when solid. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that metals are found on the left and towards the bottom of the periodic table, while non-metals are found on the right and towards the top.
    • Identifies the missing requirement: States that metalloids lie along the diagonal 'staircase' boundary between metals and non-metals, showing intermediate properties of both.
    • Identifies the missing requirement: States a valid distinguishing property, e.g. metals are generally good conductors of electricity and heat, malleable and ductile, while non-metals are generally poor conductors and brittle when solid.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

23. 23.

    Distinguish between chain isomerism and position isomerism, giving one example of each.

    [2 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Work through this mathematical step: States that chain isomers have the same molecular formula but a different arrangement of the carbon skeleton (branching), e.g. butane and methylpropane. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    3. Work through this mathematical step: States that position isomers have the same molecular formula and the same carbon skeleton, but the functional group (or substituent) is attached at a different position, e.g. propan-1-ol and propan-2-ol. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
    4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: All types of structural isomers share the same molecular formula — what differs between chain, position and functional group isomers is exactly which structural feature (skeleton, attachment point, or functional group) changes.

    Marking points

    • States that chain isomers have the same molecular formula but a different arrangement of the carbon skeleton (branching), e.g. butane and methylpropane.
    • States that position isomers have the same molecular formula and the same carbon skeleton, but the functional group (or substituent) is attached at a different position, e.g. propan-1-ol and propan-2-ol.

    Examiner tip: All types of structural isomers share the same molecular formula — what differs between chain, position and functional group isomers is exactly which structural feature (skeleton, attachment point, or functional group) changes.

24. 24.

    Marking analysis: A learner attempts the following task: “Distinguish between chain isomerism and position isomerism, giving one example of each.” Their response addresses only this point: “States that chain isomers have the same molecular formula but a different arrangement of the carbon skeleton (branching), e.g. butane and methylpropane.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [2 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that chain isomers have the same molecular formula but a different arrangement of the carbon skeleton (branching), e.g. butane and methylpropane. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that position isomers have the same molecular formula and the same carbon skeleton, but the functional group (or substituent) is attached at a different position, e.g. propan-1-ol and propan-2-ol. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that chain isomers have the same molecular formula but a different arrangement of the carbon skeleton (branching), e.g. butane and methylpropane.
    • Identifies the missing requirement: States that position isomers have the same molecular formula and the same carbon skeleton, but the functional group (or substituent) is attached at a different position, e.g. propan-1-ol and propan-2-ol.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

25. 25.

    But-1-ene and but-2-ene are structural isomers with molecular formula C₄H₈. Explain what the numbers '1' and '2' indicate, and state the type of structural isomerism this represents.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that the number indicates the position of the carbon-carbon double bond within the carbon chain. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that but-1-ene has the double bond between C1 and C2, while but-2-ene has it between C2 and C3. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that this is an example of position isomerism. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: The locant number in a molecule's name is always chosen to be as low as possible, counting from whichever end of the chain gives the substituent or double bond the lower position number.

    Marking points

    • States that the number indicates the position of the carbon-carbon double bond within the carbon chain.
    • States that but-1-ene has the double bond between C1 and C2, while but-2-ene has it between C2 and C3.
    • States that this is an example of position isomerism.

    Examiner tip: The locant number in a molecule's name is always chosen to be as low as possible, counting from whichever end of the chain gives the substituent or double bond the lower position number.

26. 26.

    Marking analysis: A learner attempts the following task: “But-1-ene and but-2-ene are structural isomers with molecular formula C₄H₈. Explain what the numbers '1' and '2' indicate, and state the type of structural isomerism this represents.” Their response addresses only this point: “States that the number indicates the position of the carbon-carbon double bond within the carbon chain.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that the number indicates the position of the carbon-carbon double bond within the carbon chain. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that but-1-ene has the double bond between C1 and C2, while but-2-ene has it between C2 and C3. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: States that this is an example of position isomerism. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that the number indicates the position of the carbon-carbon double bond within the carbon chain.
    • Identifies the missing requirement: States that but-1-ene has the double bond between C1 and C2, while but-2-ene has it between C2 and C3.
    • Identifies the missing requirement: States that this is an example of position isomerism.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

27. 27.

    Outline how ¹H NMR (proton nuclear magnetic resonance) spectroscopy can be used to determine the number of different hydrogen (proton) environments in an organic molecule.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that hydrogen atoms in different chemical environments, bonded differently within the molecule, absorb energy at slightly different frequencies in a strong magnetic field. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that this produces a separate signal (peak) in the NMR spectrum for each distinct type of hydrogen environment. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that the number of peaks observed in the spectrum therefore indicates the number of different hydrogen environments present in the molecule. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: NMR spectroscopy identifies how many distinct types of hydrogen are present, complementing IR spectroscopy (which identifies bond/functional group types) and mass spectrometry (which gives molecular mass) as tools for structure determination.

    Marking points

    • States that hydrogen atoms in different chemical environments, bonded differently within the molecule, absorb energy at slightly different frequencies in a strong magnetic field.
    • States that this produces a separate signal (peak) in the NMR spectrum for each distinct type of hydrogen environment.
    • States that the number of peaks observed in the spectrum therefore indicates the number of different hydrogen environments present in the molecule.

    Examiner tip: NMR spectroscopy identifies how many distinct types of hydrogen are present, complementing IR spectroscopy (which identifies bond/functional group types) and mass spectrometry (which gives molecular mass) as tools for structure determination.

28. 28.

    Marking analysis: A learner attempts the following task: “Outline how ¹H NMR (proton nuclear magnetic resonance) spectroscopy can be used to determine the number of different hydrogen (proton) environments in an organic molecule.” Their response addresses only this point: “States that hydrogen atoms in different chemical environments, bonded differently within the molecule, absorb energy at slightly different frequencies in a strong magnetic field.” Evaluate the response against the complete 3-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [3 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that hydrogen atoms in different chemical environments, bonded differently within the molecule, absorb energy at slightly different frequencies in a strong magnetic field. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that this produces a separate signal (peak) in the NMR spectrum for each distinct type of hydrogen environment. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: States that the number of peaks observed in the spectrum therefore indicates the number of different hydrogen environments present in the molecule. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that hydrogen atoms in different chemical environments, bonded differently within the molecule, absorb energy at slightly different frequencies in a strong magnetic field.
    • Identifies the missing requirement: States that this produces a separate signal (peak) in the NMR spectrum for each distinct type of hydrogen environment.
    • Identifies the missing requirement: States that the number of peaks observed in the spectrum therefore indicates the number of different hydrogen environments present in the molecule.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

29. 29.

    Describe and explain the general trend in melting point across period 3, from sodium to argon, in terms of the type of structure and bonding present.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Break the command into its requested parts. For each part, connect a relevant fact or observation to the conclusion it supports. Describing what happens and explaining why it happens are different tasks.
    2. Develop this part of the answer: States that Na, Mg and Al are metals with metallic bonding, with melting point increasing from Na to Al as the number of delocalised electrons per atom and ionic charge increase, strengthening the metallic bonding. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    3. Develop this part of the answer: States that Si has a giant covalent structure, giving it a very high melting point due to the large number of strong covalent bonds that must be broken. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    4. Develop this part of the answer: States that P, S, Cl and Ar exist as simple molecular (or monatomic, for Ar) substances held together only by weak van der Waals forces, giving much lower melting points. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    5. Develop this part of the answer: States that melting point therefore rises sharply to a maximum at silicon, then drops sharply and stays relatively low for the remaining simple molecular/monatomic elements. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: This period 3 melting point trend is a direct, testable illustration of how the underlying type of structure and bonding, not just position in the periodic table, ultimately determines a substance's physical properties.

    Marking points

    • States that Na, Mg and Al are metals with metallic bonding, with melting point increasing from Na to Al as the number of delocalised electrons per atom and ionic charge increase, strengthening the metallic bonding.
    • States that Si has a giant covalent structure, giving it a very high melting point due to the large number of strong covalent bonds that must be broken.
    • States that P, S, Cl and Ar exist as simple molecular (or monatomic, for Ar) substances held together only by weak van der Waals forces, giving much lower melting points.
    • States that melting point therefore rises sharply to a maximum at silicon, then drops sharply and stays relatively low for the remaining simple molecular/monatomic elements.

    Examiner tip: This period 3 melting point trend is a direct, testable illustration of how the underlying type of structure and bonding, not just position in the periodic table, ultimately determines a substance's physical properties.

30. 30.

    Marking analysis: A learner attempts the following task: “Describe and explain the general trend in melting point across period 3, from sodium to argon, in terms of the type of structure and bonding present.” Their response addresses only this point: “States that Na, Mg and Al are metals with metallic bonding, with melting point increasing from Na to Al as the number of delocalised electrons per atom and ionic charge increase, strengthening the metallic bonding.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.

    [4 marks] · no calculator

    Answer explanation

    Draft walkthroughs are based on marking guidance, not independently verified derivations.

    1. Separate the learner's stated response from the complete task. Credit only what their response demonstrates, then identify each missing requirement; do not assume unstated working.
    2. Requirement 1: Recognises credit for the stated point: States that Na, Mg and Al are metals with metallic bonding, with melting point increasing from Na to Al as the number of delocalised electrons per atom and ionic charge increase, strengthening the metallic bonding. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    3. Requirement 2: Identifies the missing requirement: States that Si has a giant covalent structure, giving it a very high melting point due to the large number of strong covalent bonds that must be broken. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    4. Requirement 3: Identifies the missing requirement: States that P, S, Cl and Ar exist as simple molecular (or monatomic, for Ar) substances held together only by weak van der Waals forces, giving much lower melting points. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    5. Requirement 4: Identifies the missing requirement: States that melting point therefore rises sharply to a maximum at silicon, then drops sharply and stays relatively low for the remaining simple molecular/monatomic elements. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
    6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

    Marking points

    • Recognises credit for the stated point: States that Na, Mg and Al are metals with metallic bonding, with melting point increasing from Na to Al as the number of delocalised electrons per atom and ionic charge increase, strengthening the metallic bonding.
    • Identifies the missing requirement: States that Si has a giant covalent structure, giving it a very high melting point due to the large number of strong covalent bonds that must be broken.
    • Identifies the missing requirement: States that P, S, Cl and Ar exist as simple molecular (or monatomic, for Ar) substances held together only by weak van der Waals forces, giving much lower melting points.
    • Identifies the missing requirement: States that melting point therefore rises sharply to a maximum at silicon, then drops sharply and stays relatively low for the remaining simple molecular/monatomic elements.

    Examiner tip: Treat each marking point as a separate requirement. Do not award the same idea twice, and do not infer work the learner did not show.

Original, unofficial practice questions from SubjectScout — not official past-paper questions.