AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Higher), 2024: Question 3

Mark scheme

Show the mark scheme

Question 3

AO /

Question Answers Mark

Spec. Ref.

03 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 3 6

How to answer it

Comparing Sodium Chloride and Oxygen

What this question tests

Comparing structure and bonding in an ionic substance and a simple covalent substance. You need to describe similarities and differences clearly, using terms such as giant ionic lattice, small molecule, ionic bonding, covalent bonding, electron transfer, and shared electrons.

Question 03 6 marks

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

How to access the top level

✅ Correct answers

Sodium chloride has a giant ionic structure / lattice of ions.
It contains oppositely charged ions (Na⁺ and Cl⁻).
It has ionic bonding.
These ions form because electrons are transferred from sodium atoms to chlorine atoms.
Oxygen is a small / simple molecular substance.
It is an element, whereas sodium chloride is a compound made from two elements.
In oxygen, the atoms are joined by covalent bonds.
In O₂, electrons are shared between oxygen atoms.
There is a double covalent bond in each oxygen molecule.
There are weak forces between oxygen molecules.
Similarity: both have strong bonds within their structures.
Similarity: the particles have full outer shells.

💡 Key knowledge

Ionic bonding = attraction between oppositely charged ions.
Covalent bonding = shared pair(s) of electrons.
Giant ionic lattice means a repeating 3D arrangement of ions.
Simple molecular means small molecules with strong covalent bonds inside each molecule but weak intermolecular forces between molecules.
NaCl is not made of molecules.
O₂ is a molecule made of two oxygen atoms.

🧠 Exam technique

This is a compare question, so do not just describe sodium chloride and then stop.
Use linking words such as whereas, however, both, in contrast.
To reach Level 2 (4–6 marks), the mark scheme says you must compare the structure or bonding of both substances and include a sense of magnitude, for example:
- NaCl is a giant structure, whereas oxygen is a small molecule.
- Oxygen has weak forces between molecules, unlike sodium chloride’s giant ionic lattice.
Best answers include at least one similarity and several clear differences.

❌ Common errors

Saying sodium chloride is made of molecules — it is not; it is a giant ionic lattice.
Saying oxygen contains ions — it does not; it is covalent.
Forgetting to compare both substances directly.
Saying oxygen has “weak bonds” without being precise. The covalent bond inside O₂ is strong; the forces between molecules are weak.
Missing the point that NaCl is a compound but O₂ is an element.

A strong comparison plan

Feature	Sodium chloride, NaCl	Oxygen, O₂
Type of substance	Compound made from two elements	Element
Structure	Giant ionic lattice	Small / simple molecular
Bonding	Ionic bonding	Covalent bonding
How bonding forms	Electrons are transferred from sodium to chlorine	Electrons are shared between oxygen atoms
Particles present	Na⁺ and Cl⁻ ions	O₂ molecules made of oxygen atoms
Other detail	Oppositely charged ions attract strongly	Double bond in O₂ and weak forces between molecules

✅ Model full-mark answer

Sodium chloride and oxygen both have strong bonds and their particles have full outer shells. However, sodium chloride is a compound made from two elements, while oxygen is an element.

Sodium chloride has a giant ionic lattice containing Na⁺ and Cl⁻ ions. The bonding is ionic, formed because electrons are transferred from sodium atoms to chlorine atoms. There are strong electrostatic attractions between the oppositely charged ions in all directions.

Oxygen is a small molecule. It is covalent, so the oxygen atoms are joined by shared electrons. In each O₂ molecule there is a double covalent bond. Unlike sodium chloride, oxygen has weak forces between molecules.

🧠 Why this scores highly

It compares both substances throughout.
It covers structure and bonding.
It includes precise scientific terms: giant ionic lattice, small molecule, ionic, covalent, transferred, shared.
It includes magnitude: giant vs small, weak forces between molecules vs giant lattice.
This is exactly the kind of detail that separates a top Level 2 response from a basic answer.

💡 Mark breakdown and level guidance

Level 2: 4–6 marks
Scientifically relevant features are identified and the similarities/differences are made clear. The best responses compare the substances directly and show the size/type difference, such as giant ionic lattice versus small molecule.

Level 1: 1–3 marks
Some relevant points are given, but the comparison is limited or incomplete. For example, a student may say sodium chloride is ionic and oxygen is covalent, but not explain the structures clearly.

0 marks
No relevant scientific content.

❌ Examiner insight

Students often lost marks by giving isolated facts instead of a true comparison.
Another common issue was confusing bonds within molecules with forces between molecules.
Top responses clearly stated that sodium chloride is giant and oxygen is small/simple molecular.
Using the word double bond for O₂ can strengthen the answer, but only if the rest of the comparison is correct.

📐 Calculations

No calculation is needed for this question. Focus on accurate scientific vocabulary and direct comparison.

Topics

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