IB · CHEMISTRY SL

Chemistry SL

Structure 1: models of particulate nature of matter — Structure 1

Name: ____________________Date: October 10, 2026

1.
State the three states of matter, and describe the arrangement and movement of particles in each.
[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 solid, liquid and gas as the three states of matter. 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 in a solid, particles are closely packed in a fixed, regular arrangement, only vibrating about fixed positions; in a liquid, particles are close but can move past one another. 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 in a gas, particles are far apart, moving freely and randomly at high speed with negligible forces between them. 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: Always describe both particle spacing/arrangement and movement for full marks in kinetic particle theory questions.
Marking points
- States solid, liquid and gas as the three states of matter.
- States that in a solid, particles are closely packed in a fixed, regular arrangement, only vibrating about fixed positions; in a liquid, particles are close but can move past one another.
- States that in a gas, particles are far apart, moving freely and randomly at high speed with negligible forces between them.
Examiner tip: Always describe both particle spacing/arrangement and movement for full marks in kinetic particle theory questions.
2.
Marking analysis: A learner attempts the following task: “State the three states of matter, and describe the arrangement and movement of particles in each.” Their response addresses only this point: “States solid, liquid and gas as the three states of matter.” 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 solid, liquid and gas as the three states of matter. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that in a solid, particles are closely packed in a fixed, regular arrangement, only vibrating about fixed positions; in a liquid, particles are close but can move past one another. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that in a gas, particles are far apart, moving freely and randomly at high speed with negligible forces between them. 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 solid, liquid and gas as the three states of matter.
- Identifies the missing requirement: States that in a solid, particles are closely packed in a fixed, regular arrangement, only vibrating about fixed positions; in a liquid, particles are close but can move past one another.
- Identifies the missing requirement: States that in a gas, particles are far apart, moving freely and randomly at high speed with negligible forces between them.
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.
An atom of chlorine-35 has atomic number 17. State the number of protons, neutrons and electrons it contains.
[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 17 protons (equal to the 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 18 neutrons (mass number minus atomic number: 35 − 17). 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 17 electrons (equal to the number of protons in a neutral atom). 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: In a neutral atom, the number of electrons always equals the number of protons; only ions have unequal numbers.
Marking points
- States 17 protons (equal to the atomic number).
- States 18 neutrons (mass number minus atomic number: 35 − 17).
- States 17 electrons (equal to the number of protons in a neutral atom).
Examiner tip: In a neutral atom, the number of electrons always equals the number of protons; only ions have unequal numbers.
4.
Marking analysis: A learner attempts the following task: “An atom of chlorine-35 has atomic number 17. State the number of protons, neutrons and electrons it contains.” Their response addresses only this point: “States 17 protons (equal to the 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 17 protons (equal to the atomic number). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States 18 neutrons (mass number minus atomic number: 35 − 17). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States 17 electrons (equal to the number of protons in a neutral atom). 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 17 protons (equal to the atomic number).
- Identifies the missing requirement: States 18 neutrons (mass number minus atomic number: 35 − 17).
- Identifies the missing requirement: States 17 electrons (equal to the number of protons in a neutral atom).
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.
Chlorine contains 75% chlorine-35 and 25% chlorine-37. Calculate its relative atomic mass.
[3 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Work through this mathematical step: Uses a weighted-average calculation with the given percentages as weights. 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: Calculates (0.75 × 35) + (0.25 × 37). 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: Obtains 35.5. 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: Relative atomic mass is always a weighted average of isotopic masses, weighted by their natural abundance as decimal fractions.
Marking points
- Uses a weighted-average calculation with the given percentages as weights.
- Calculates (0.75 × 35) + (0.25 × 37).
- Obtains 35.5.
Examiner tip: Relative atomic mass is always a weighted average of isotopic masses, weighted by their natural abundance as decimal fractions.
6.
Marking analysis: A learner attempts the following task: “Chlorine contains 75% chlorine-35 and 25% chlorine-37. Calculate its relative atomic mass.” Their response addresses only this point: “Uses a weighted-average calculation with the given percentages as weights.” 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: Uses a weighted-average calculation with the given percentages as weights. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Calculates (0.75 × 35) + (0.25 × 37). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Obtains 35.5. 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: Uses a weighted-average calculation with the given percentages as weights.
- Identifies the missing requirement: Calculates (0.75 × 35) + (0.25 × 37).
- Identifies the missing requirement: Obtains 35.5.
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.
Write the full electron configuration of a phosphorus atom (atomic number 15) using subshell notation.
[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: Fills 1s² 2s² 2p⁶ correctly (10 electrons). 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: Fills 3s² correctly. 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: Completes the configuration as 1s² 2s² 2p⁶ 3s² 3p³. 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: Fill subshells in order of increasing energy (1s, 2s, 2p, 3s, 3p...) and check the total electron count matches the atomic number.
Marking points
- Fills 1s² 2s² 2p⁶ correctly (10 electrons).
- Fills 3s² correctly.
- Completes the configuration as 1s² 2s² 2p⁶ 3s² 3p³.
Examiner tip: Fill subshells in order of increasing energy (1s, 2s, 2p, 3s, 3p...) and check the total electron count matches the atomic number.
8.
Marking analysis: A learner attempts the following task: “Write the full electron configuration of a phosphorus atom (atomic number 15) using subshell notation.” Their response addresses only this point: “Fills 1s² 2s² 2p⁶ correctly (10 electrons).” 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: Fills 1s² 2s² 2p⁶ correctly (10 electrons). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Fills 3s² correctly. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Completes the configuration as 1s² 2s² 2p⁶ 3s² 3p³. 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: Fills 1s² 2s² 2p⁶ correctly (10 electrons).
- Identifies the missing requirement: Fills 3s² correctly.
- Identifies the missing requirement: Completes the configuration as 1s² 2s² 2p⁶ 3s² 3p³.
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.
Explain why successive ionization energies of an element always increase, and how a large jump between two successive values provides evidence for electron shell structure.
[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 each successive electron is removed from an increasingly positively charged ion, requiring more energy. 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 a large jump occurs when the next electron removed comes from a shell closer to the nucleus (a lower 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 electrons in an inner shell experience much less shielding and much stronger nuclear attraction, requiring significantly more energy to remove. 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 position of large jumps in successive ionization energy data directly reveals how many electrons are in each shell.
Marking points
- States that each successive electron is removed from an increasingly positively charged ion, requiring more energy.
- States that a large jump occurs when the next electron removed comes from a shell closer to the nucleus (a lower principal energy level).
- States that electrons in an inner shell experience much less shielding and much stronger nuclear attraction, requiring significantly more energy to remove.
Examiner tip: The position of large jumps in successive ionization energy data directly reveals how many electrons are in each shell.
10.
Marking analysis: A learner attempts the following task: “Explain why successive ionization energies of an element always increase, and how a large jump between two successive values provides evidence for electron shell structure.” Their response addresses only this point: “States that each successive electron is removed from an increasingly positively charged ion, requiring more energy.” 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 each successive electron is removed from an increasingly positively charged ion, requiring more energy. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that a large jump occurs when the next electron removed comes from a shell closer to the nucleus (a lower 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 electrons in an inner shell experience much less shielding and much stronger nuclear attraction, requiring significantly more energy to remove. 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 each successive electron is removed from an increasingly positively charged ion, requiring more energy.
- Identifies the missing requirement: States that a large jump occurs when the next electron removed comes from a shell closer to the nucleus (a lower principal energy level).
- Identifies the missing requirement: States that electrons in an inner shell experience much less shielding and much stronger nuclear attraction, requiring significantly more energy to remove.
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.
Calculate the number of moles in 5.85 g of sodium chloride, NaCl. Use Ar: Na = 23.0, Cl = 35.5.
[3 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Work through this mathematical step: Calculates Mr(NaCl) = 23.0 + 35.5 = 58.5. 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: Uses amount = mass ÷ relative formula mass. 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: Obtains 0.100 mol. 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: Add the relative atomic masses before dividing the sample mass — the particulate-nature strand links directly to quantitative mole calculations.
Marking points
- Calculates Mr(NaCl) = 23.0 + 35.5 = 58.5.
- Uses amount = mass ÷ relative formula mass.
- Obtains 0.100 mol.
Examiner tip: Add the relative atomic masses before dividing the sample mass — the particulate-nature strand links directly to quantitative mole calculations.
12.
Marking analysis: A learner attempts the following task: “Calculate the number of moles in 5.85 g of sodium chloride, NaCl. Use Ar: Na = 23.0, Cl = 35.5.” Their response addresses only this point: “Calculates Mr(NaCl) = 23.0 + 35.5 = 58.5.” 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: Calculates Mr(NaCl) = 23.0 + 35.5 = 58.5. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Uses amount = mass ÷ relative formula mass. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Obtains 0.100 mol. 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: Calculates Mr(NaCl) = 23.0 + 35.5 = 58.5.
- Identifies the missing requirement: Uses amount = mass ÷ relative formula mass.
- Identifies the missing requirement: Obtains 0.100 mol.
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.
State Avogadro's constant and use it to calculate the number of molecules in 0.25 mol of water.
[3 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Develop this part of the answer: States Avogadro's constant as 6.02 × 10²³ per mole. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Work through this mathematical step: Uses number of molecules = moles × Avogadro's constant. 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: Obtains 1.51 × 10²³ molecules. 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: Avogadro's constant links the mole to a count of actual particles — always multiply (not divide) moles by it to get the number of particles.
Marking points
- States Avogadro's constant as 6.02 × 10²³ per mole.
- Uses number of molecules = moles × Avogadro's constant.
- Obtains 1.51 × 10²³ molecules.
Examiner tip: Avogadro's constant links the mole to a count of actual particles — always multiply (not divide) moles by it to get the number of particles.
14.
Marking analysis: A learner attempts the following task: “State Avogadro's constant and use it to calculate the number of molecules in 0.25 mol of water.” Their response addresses only this point: “States Avogadro's constant as 6.02 × 10²³ per mole.” 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 Avogadro's constant as 6.02 × 10²³ per mole. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Uses number of molecules = moles × Avogadro's constant. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Obtains 1.51 × 10²³ molecules. 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 Avogadro's constant as 6.02 × 10²³ per mole.
- Identifies the missing requirement: Uses number of molecules = moles × Avogadro's constant.
- Identifies the missing requirement: Obtains 1.51 × 10²³ molecules.
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.
Outline why successive ionization energies show a general increasing trend across each shell, but sub-shell structure (s, p) causes small irregularities within a shell.
[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: States that within a shell, ionization energy generally increases as electrons are removed from progressively more stable (lower-energy) sub-shells. 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 a small drop can occur when comparing a filled or half-filled p sub-shell (extra stability) to the next p electron, reflecting sub-shell energy differences. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
4. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: These small irregularities are strong evidence for sub-shell structure (s, p, d, f), a finer level of detail than the shell structure alone explains.
Marking points
- States that within a shell, ionization energy generally increases as electrons are removed from progressively more stable (lower-energy) sub-shells.
- States that a small drop can occur when comparing a filled or half-filled p sub-shell (extra stability) to the next p electron, reflecting sub-shell energy differences.
Examiner tip: These small irregularities are strong evidence for sub-shell structure (s, p, d, f), a finer level of detail than the shell structure alone explains.
16.
Marking analysis: A learner attempts the following task: “Outline why successive ionization energies show a general increasing trend across each shell, but sub-shell structure (s, p) causes small irregularities within a shell.” Their response addresses only this point: “States that within a shell, ionization energy generally increases as electrons are removed from progressively more stable (lower-energy) sub-shells.” 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 within a shell, ionization energy generally increases as electrons are removed from progressively more stable (lower-energy) sub-shells. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that a small drop can occur when comparing a filled or half-filled p sub-shell (extra stability) to the next p electron, reflecting sub-shell energy differences. 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 within a shell, ionization energy generally increases as electrons are removed from progressively more stable (lower-energy) sub-shells.
- Identifies the missing requirement: States that a small drop can occur when comparing a filled or half-filled p sub-shell (extra stability) to the next p electron, reflecting sub-shell energy differences.
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.
Calculate the empirical formula of a compound containing 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Use Ar: C = 12, H = 1, O = 16.
[4 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Work through this mathematical step: Divides each percentage by its relative atomic mass: C = 40/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33. 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: Divides each result by the smallest value (3.33): C = 1, H = 2.01, O = 1. 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: Rounds to whole-number ratios: C:H:O = 1:2:1. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
5. Work through this mathematical step: States the empirical formula as CH₂O. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
6. Check the complete task again, including restrictions, units, precision and supporting evidence when relevant. Specific caution: Always divide by the atomic mass first (to get moles of each element), then divide by the smallest mole value to get the simplest whole-number ratio.
Marking points
- Divides each percentage by its relative atomic mass: C = 40/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33.
- Divides each result by the smallest value (3.33): C = 1, H = 2.01, O = 1.
- Rounds to whole-number ratios: C:H:O = 1:2:1.
- States the empirical formula as CH₂O.
Examiner tip: Always divide by the atomic mass first (to get moles of each element), then divide by the smallest mole value to get the simplest whole-number ratio.
18.
Marking analysis: A learner attempts the following task: “Calculate the empirical formula of a compound containing 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Use Ar: C = 12, H = 1, O = 16.” Their response addresses only this point: “Divides each percentage by its relative atomic mass: C = 40/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 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: Divides each percentage by its relative atomic mass: C = 40/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Divides each result by the smallest value (3.33): C = 1, H = 2.01, O = 1. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Rounds to whole-number ratios: C:H:O = 1:2:1. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Requirement 4: Identifies the missing requirement: States the empirical formula as CH₂O. 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: Divides each percentage by its relative atomic mass: C = 40/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33.
- Identifies the missing requirement: Divides each result by the smallest value (3.33): C = 1, H = 2.01, O = 1.
- Identifies the missing requirement: Rounds to whole-number ratios: C:H:O = 1:2:1.
- Identifies the missing requirement: States the empirical formula as CH₂O.
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.
A mass spectrum of an element shows two peaks: one at mass/charge 63 (69.2%) and one at 65 (30.8%). Identify what these two peaks represent and calculate the relative atomic mass of the element.
[4 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Develop this part of the answer: States that the two peaks represent two different isotopes of the same element. Show which detail or principle supports it and how it addresses the command; equivalent supported wording is acceptable.
3. Work through this mathematical step: Uses a weighted-average calculation with the given abundances. 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: Calculates (0.692 × 63) + (0.308 × 65). Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
5. Develop this part of the answer: Obtains a relative atomic mass of approximately 63.6 (consistent with copper). 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: Mass spectrometry directly measures the mass and relative abundance of each isotope present, exactly the data needed for a relative-atomic-mass calculation.
Marking points
- States that the two peaks represent two different isotopes of the same element.
- Uses a weighted-average calculation with the given abundances.
- Calculates (0.692 × 63) + (0.308 × 65).
- Obtains a relative atomic mass of approximately 63.6 (consistent with copper).
Examiner tip: Mass spectrometry directly measures the mass and relative abundance of each isotope present, exactly the data needed for a relative-atomic-mass calculation.
20.
Marking analysis: A learner attempts the following task: “A mass spectrum of an element shows two peaks: one at mass/charge 63 (69.2%) and one at 65 (30.8%). Identify what these two peaks represent and calculate the relative atomic mass of the element.” Their response addresses only this point: “States that the two peaks represent two different isotopes of the same element.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 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 two peaks represent two different isotopes of the same element. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Uses a weighted-average calculation with the given abundances. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Calculates (0.692 × 63) + (0.308 × 65). Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Requirement 4: Identifies the missing requirement: Obtains a relative atomic mass of approximately 63.6 (consistent with copper). 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 the two peaks represent two different isotopes of the same element.
- Identifies the missing requirement: Uses a weighted-average calculation with the given abundances.
- Identifies the missing requirement: Calculates (0.692 × 63) + (0.308 × 65).
- Identifies the missing requirement: Obtains a relative atomic mass of approximately 63.6 (consistent with copper).
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.
Calculate the volume occupied by 0.75 mol of oxygen gas at standard temperature and pressure (STP), given that 1 mole of any gas occupies 22.7 dm³ at STP.
[2 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Work through this mathematical step: Uses volume = moles × 22.7 dm³. 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: Obtains volume = 0.75 × 22.7 ≈ 17.0 dm³. 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: The molar gas volume applies to any gas at the same temperature and pressure, regardless of its identity, since it depends only on the number of particles present, not their type.
Marking points
- Uses volume = moles × 22.7 dm³.
- Obtains volume = 0.75 × 22.7 ≈ 17.0 dm³.
Examiner tip: The molar gas volume applies to any gas at the same temperature and pressure, regardless of its identity, since it depends only on the number of particles present, not their type.
22.
Marking analysis: A learner attempts the following task: “Calculate the volume occupied by 0.75 mol of oxygen gas at standard temperature and pressure (STP), given that 1 mole of any gas occupies 22.7 dm³ at STP.” Their response addresses only this point: “Uses volume = moles × 22.7 dm³.” Evaluate the response against the complete 2-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[2 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: Uses volume = moles × 22.7 dm³. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Obtains volume = 0.75 × 22.7 ≈ 17.0 dm³. 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: Uses volume = moles × 22.7 dm³.
- Identifies the missing requirement: Obtains volume = 0.75 × 22.7 ≈ 17.0 dm³.
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.
Calculate the percentage by mass of nitrogen in ammonium nitrate, NH₄NO₃. Use Ar: N = 14, H = 1, O = 16.
[4 marks]
Answer explanation
Draft walkthroughs are based on marking guidance, not independently verified derivations.
1. List the given quantities and the requested unknown. Choose the relation that connects them, state any required assumptions, then substitute before rounding. Preserve exact expressions when the task asks for an exact result.
2. Work through this mathematical step: Calculates Mr(NH₄NO₃) = 14 + 4(1) + 14 + 3(16) = 80. 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: Identifies that there are 2 nitrogen atoms in the formula, giving a total nitrogen mass of 2 × 14 = 28. 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: Uses percentage = (mass of nitrogen ÷ Mr) × 100 = (28/80) × 100. Write the intermediate operation, keep the units consistent where applicable, and check the relation against the quantities given in the question.
5. Develop this part of the answer: Obtains 35%. 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: Ammonium nitrate's high nitrogen content is exactly why it is widely used as an agricultural fertiliser — always double-check for repeated atoms of the element of interest across the whole formula, not just one part of it.
Marking points
- Calculates Mr(NH₄NO₃) = 14 + 4(1) + 14 + 3(16) = 80.
- Identifies that there are 2 nitrogen atoms in the formula, giving a total nitrogen mass of 2 × 14 = 28.
- Uses percentage = (mass of nitrogen ÷ Mr) × 100 = (28/80) × 100.
- Obtains 35%.
Examiner tip: Ammonium nitrate's high nitrogen content is exactly why it is widely used as an agricultural fertiliser — always double-check for repeated atoms of the element of interest across the whole formula, not just one part of it.
24.
Marking analysis: A learner attempts the following task: “Calculate the percentage by mass of nitrogen in ammonium nitrate, NH₄NO₃. Use Ar: N = 14, H = 1, O = 16.” Their response addresses only this point: “Calculates Mr(NH₄NO₃) = 14 + 4(1) + 14 + 3(16) = 80.” Evaluate the response against the complete 4-mark task. Identify what earns credit and state every additional requirement needed for full marks.
[4 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: Calculates Mr(NH₄NO₃) = 14 + 4(1) + 14 + 3(16) = 80. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: Identifies that there are 2 nitrogen atoms in the formula, giving a total nitrogen mass of 2 × 14 = 28. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: Uses percentage = (mass of nitrogen ÷ Mr) × 100 = (28/80) × 100. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
5. Requirement 4: Identifies the missing requirement: Obtains 35%. 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: Calculates Mr(NH₄NO₃) = 14 + 4(1) + 14 + 3(16) = 80.
- Identifies the missing requirement: Identifies that there are 2 nitrogen atoms in the formula, giving a total nitrogen mass of 2 × 14 = 28.
- Identifies the missing requirement: Uses percentage = (mass of nitrogen ÷ Mr) × 100 = (28/80) × 100.
- Identifies the missing requirement: Obtains 35%.
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.
Write the electron configuration of the Na⁺ ion (sodium, atomic number 11), and state which noble gas has the same 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 the electron configuration of the neutral sodium atom: 1s² 2s² 2p⁶ 3s¹. 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 the Na⁺ ion forms by losing the single 3s electron, giving the configuration 1s² 2s² 2p⁶. 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 the same electron configuration as the noble gas neon (Ne). 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: Metal ions typically lose electrons to achieve a full outer shell matching the nearest preceding noble gas — this drive towards a stable noble-gas configuration explains why Na consistently forms a 1+ ion, never 2+ or 3+.
Marking points
- States the electron configuration of the neutral sodium atom: 1s² 2s² 2p⁶ 3s¹.
- States that the Na⁺ ion forms by losing the single 3s electron, giving the configuration 1s² 2s² 2p⁶.
- States that this is the same electron configuration as the noble gas neon (Ne).
Examiner tip: Metal ions typically lose electrons to achieve a full outer shell matching the nearest preceding noble gas — this drive towards a stable noble-gas configuration explains why Na consistently forms a 1+ ion, never 2+ or 3+.
26.
Marking analysis: A learner attempts the following task: “Write the electron configuration of the Na⁺ ion (sodium, atomic number 11), and state which noble gas has the same electron configuration.” Their response addresses only this point: “States the electron configuration of the neutral sodium atom: 1s² 2s² 2p⁶ 3s¹.” 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 electron configuration of the neutral sodium atom: 1s² 2s² 2p⁶ 3s¹. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that the Na⁺ ion forms by losing the single 3s electron, giving the configuration 1s² 2s² 2p⁶. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that this is the same electron configuration as the noble gas neon (Ne). 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 electron configuration of the neutral sodium atom: 1s² 2s² 2p⁶ 3s¹.
- Identifies the missing requirement: States that the Na⁺ ion forms by losing the single 3s electron, giving the configuration 1s² 2s² 2p⁶.
- Identifies the missing requirement: States that this is the same electron configuration as the noble gas neon (Ne).
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.
Describe and explain the general trend in first ionization energy across period 3 (Na to Ar), in terms of nuclear charge and atomic radius.
[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 first ionisation energy generally increases across the period from Na to Ar. 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 nuclear charge increases across the period, while electrons are added to the same outer shell, with similar shielding. 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 increased nuclear attraction, along with a decreasing atomic radius, makes it harder to remove an outer electron, increasing ionisation energy. 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: Shielding stays roughly constant across a period, since no new inner shells are added — this is exactly why increasing nuclear charge alone is enough to explain the overall upward trend.
Marking points
- States that first ionisation energy generally increases across the period from Na to Ar.
- States that nuclear charge increases across the period, while electrons are added to the same outer shell, with similar shielding.
- States that this increased nuclear attraction, along with a decreasing atomic radius, makes it harder to remove an outer electron, increasing ionisation energy.
Examiner tip: Shielding stays roughly constant across a period, since no new inner shells are added — this is exactly why increasing nuclear charge alone is enough to explain the overall upward trend.
28.
Marking analysis: A learner attempts the following task: “Describe and explain the general trend in first ionization energy across period 3 (Na to Ar), in terms of nuclear charge and atomic radius.” Their response addresses only this point: “States that first ionisation energy generally increases across the period from Na to Ar.” 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 first ionisation energy generally increases across the period from Na to Ar. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that nuclear charge increases across the period, while electrons are added to the same outer shell, with similar shielding. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that this increased nuclear attraction, along with a decreasing atomic radius, makes it harder to remove an outer electron, increasing ionisation energy. 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 first ionisation energy generally increases across the period from Na to Ar.
- Identifies the missing requirement: States that nuclear charge increases across the period, while electrons are added to the same outer shell, with similar shielding.
- Identifies the missing requirement: States that this increased nuclear attraction, along with a decreasing atomic radius, makes it harder to remove an outer electron, increasing ionisation energy.
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.
Explain why first ionization energy decreases down group 1 of the periodic table (Li to Cs), in terms of atomic radius and shielding.
[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 atomic radius increases down the group, as electrons occupy additional shells further from the nucleus. 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 increased electron shielding from additional inner shells reduces the effective nuclear attraction felt by the outer electron. 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 both increased distance and increased shielding make it easier to remove the outer electron, decreasing first ionisation energy down the 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: Down a group, increasing shielding and increasing radius both act in the same direction, decreasing ionisation energy — while across a period, increasing nuclear charge dominates over roughly constant shielding, increasing it.
Marking points
- States that atomic radius increases down the group, as electrons occupy additional shells further from the nucleus.
- States that increased electron shielding from additional inner shells reduces the effective nuclear attraction felt by the outer electron.
- States that both increased distance and increased shielding make it easier to remove the outer electron, decreasing first ionisation energy down the group.
Examiner tip: Down a group, increasing shielding and increasing radius both act in the same direction, decreasing ionisation energy — while across a period, increasing nuclear charge dominates over roughly constant shielding, increasing it.
30.
Marking analysis: A learner attempts the following task: “Explain why first ionization energy decreases down group 1 of the periodic table (Li to Cs), in terms of atomic radius and shielding.” Their response addresses only this point: “States that atomic radius increases down the group, as electrons occupy additional shells further from the nucleus.” 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 atomic radius increases down the group, as electrons occupy additional shells further from the nucleus. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
3. Requirement 2: Identifies the missing requirement: States that increased electron shielding from additional inner shells reduces the effective nuclear attraction felt by the outer electron. Compare this requirement with the supplied learner response; missing evidence cannot earn credit.
4. Requirement 3: Identifies the missing requirement: States that both increased distance and increased shielding make it easier to remove the outer electron, decreasing first ionisation energy down the 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 atomic radius increases down the group, as electrons occupy additional shells further from the nucleus.
- Identifies the missing requirement: States that increased electron shielding from additional inner shells reduces the effective nuclear attraction felt by the outer electron.
- Identifies the missing requirement: States that both increased distance and increased shielding make it easier to remove the outer electron, decreasing first ionisation energy down the 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.