AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2024: Question 8

6 marks · Standard Demand difficulty · Extended Answer

Compare the structure and bonding of sodium chloride and oxygen.

Practise this question

Question

The question page shows Table 8 with two columns labelled Substance and Structure. One row shows sodium chloride, NaCl, with a diagram of a giant ionic lattice made of alternating large grey negative ions and smaller white positive ions marked with minus and plus signs; another row shows oxygen, O2, as two joined circles representing a diatomic molecule. Beneath the table, the instruction says 'Compare the structure and bonding of sodium chloride and oxygen.' and the question is worth 6 marks, followed by several blank writing lines for an extended response.
Question text

08 Table 8 shows diagrams which represent the structures of two substances.

Table 8

Compare the structure and bonding of sodium chloride and oxygen.

[6 marks]

Mark scheme

Show the mark scheme The mark scheme for Question 08 uses level-based marking: Level 2 earns 4–6 marks for identifying scientifically relevant features and clearly comparing similarities and differences, while Level 1 earns 1–3 marks for identifying relevant features and noting differences; no relevant content scores 0. Indicative content states that both substances have strong bonds and full outer shells, but sodium chloride is a compound made from two elements with a giant ionic structure of oppositely charged ions formed by electron transfer, whereas oxygen is an element made of small molecules with atoms joined by a double covalent bond through shared electrons and weak forces between molecules. A note adds that for Level 2 there must be comparison of the structure or bonding of both sodium chloride and oxygen, including magnitude of difference where appropriate.

Question 8

AO /

Question Answers Mark

Spec. Ref.

08 Level 2: Scientifically relevant features are identified; the way(s) in 4‒6 AO1

which they are similar/different is made clear and (where 5.2.1.1

appropriate) the magnitude of the similarity/difference is noted. 5.2.1.2

5.2.1.3

5.2.1.4

Level 1: Relevant features are identified and differences noted. 1‒3 5.2.2.3

5.2.2.4

No relevant content 0

Indicative content:

Similarities

• both have strong bonds

• particles have full outer shells

Differences

• sodium chloride is a compound

• sodium chloride is made from two elements

• oxygen is an element

• sodium chloride is a giant structure of ions

• oxygen is a small molecule

• sodium chloride has ionic bonds

• sodium chloride consists of oppositely charged ions

• electrons are transferred from sodium atoms to chlorine atoms

• oxygen is covalent

• oxygen (molecules) are made up of oxygen atoms

• joined by double covalent bond

• electrons are shared between oxygen atoms

• with weak forces between oxygen molecules

For Level 2, there must be a comparison of either the structure or

bonding of both sodium chloride and oxygen, and a description of

magnitude.

Total Question 8 6

How to answer it

GCSE AQA Combined Science: Trilogy — Question 8

Comparing the structure and bonding of sodium chloride and oxygen

What this question tests

You need to compare structure and bonding in two different substances. The key skills are: spotting that sodium chloride is a giant ionic lattice, recognising that oxygen is a small covalent molecule, and using correct scientific vocabulary to make clear comparisons. To reach the top marks, make sure you compare both substances directly and explain at least one similarity and one difference.

Overall exam focus

💡 Key knowledge

  • NaCl is an ionic compound.
  • It has a giant lattice of oppositely charged ions.
  • O₂ is a small molecule made from two oxygen atoms.
  • Oxygen atoms are joined by a double covalent bond.
  • Both substances have strong bonds and particles with full outer shells.

🧠 Exam technique

  • Use comparison words: “whereas”, “however”, “in contrast”.
  • Do not just describe one substance on its own.
  • To get Level 2, show a clear similarity and a clear difference.
  • Use correct particle language: ions for NaCl, molecules for O₂.

❌ Common errors

  • Saying sodium chloride is made of molecules.
  • Saying oxygen is ionic.
  • Mixing up ions and atoms.
  • Forgetting that oxygen is a small molecule, not a giant structure.

Mark scheme breakdown

📐 How the 6 marks are awarded

  • Level 1 (1–3 marks): some relevant features are identified, with basic differences.
  • Level 2 (4–6 marks): scientifically relevant features are identified and the similarity/difference is made clear.
  • Top answers compare both structure and bonding and may mention the size/magnitude of the structure difference: giant lattice vs small molecule.

Part (a): Compare the structure and bonding of sodium chloride and oxygen

✅ Correct answer

Sodium chloride is a giant ionic lattice made of oppositely charged ions. The ions are held together by strong ionic bonds. Oxygen is a small molecule made of two oxygen atoms. The atoms in oxygen are held together by a double covalent bond.

Both substances have strong bonds within their structures and the particles have full outer shells. However, sodium chloride is a compound made from two elements, while oxygen is an element.

💡 Key knowledge

  • Ionic bonding = attraction between positive and negative ions.
  • Covalent bonding = shared pair(s) of electrons between atoms.
  • Giant structure = lots of particles joined in a repeating arrangement.
  • Small molecule = only a few atoms joined together.
  • In oxygen, electrons are shared; in sodium chloride, electrons are transferred from sodium to chlorine.

🧠 How to write a top-band comparison

  • Start with NaCl, then compare with O₂.
  • Include both structure and bonding.
  • Make the difference clear: giant lattice versus small molecule.
  • To show strong understanding, mention that both have full outer shells but get them in different ways.

❌ Common examiner-flagged mistakes

  • “Sodium chloride is a big molecule” — incorrect. It is a giant ionic lattice.
  • “Oxygen has ionic bonds” — incorrect. It has covalent bonding.
  • “Both are compounds” — incorrect. Oxygen is an element.
  • Talking only about the diagram and not the bonding.

📐 What to mention if you are aiming for full marks

  1. State NaCl is ionic.
  2. State O₂ is covalent.
  3. Compare the size/structure. NaCl is giant; O₂ is small.
  4. Compare the particles. NaCl has ions; O₂ has atoms in molecules.
  5. Describe the bonding. ionic attraction vs shared electrons.
  6. Add a similarity. both have strong bonds and full outer shells.

Model answer you could adapt in the exam

Sodium chloride has a giant ionic lattice of oppositely charged ions held together by strong ionic bonds. Oxygen is a small molecule made of two oxygen atoms joined by a double covalent bond. Both substances have strong bonds and their particles have full outer shells, but sodium chloride is a compound made from two elements, whereas oxygen is an element.

Why this answer scores highly

✅ What the examiner wants

  • Correct scientific vocabulary.
  • Direct comparison of both substances.
  • A clear structural contrast: giant lattice vs small molecule.
  • A bonding contrast: ionic vs covalent.

🧠 Final exam tip

If you are unsure, always compare: what the particles are, how they are held together, and how big the structure is. That usually covers enough points for this question.

Quick recall summary

  • NaCl: giant ionic lattice, ions, ionic bonds, compound, two elements.
  • O₂: small molecule, covalent bond, element, two oxygen atoms.
  • Similarity: both have strong bonds and full outer shells.

Topics

Chemistry · C2: Bonding, Structure and the Properties of Matter

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Chemistry Paper 1 (Foundation), 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.