AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Foundation), 2024: Question 2

💡 Key knowledge

• Carbon atoms form 4 covalent bonds in many compounds.
• In methane, each H atom forms 1 bond and carbon forms 4 single bonds.
• Diamond = each carbon bonded to 4 others in a giant covalent lattice.
• Graphite = each carbon bonded to 3 others, leaving delocalised electrons.
• Fullerenes are hollow carbon structures with hexagonal rings.

🧠 Exam technique

• For structure questions, use the diagram clues and the bonding pattern.
• If asked to “describe”, give two clear points for two marks.
• When naming charge carriers in graphite, say delocalised electrons or free electrons.
• Tick questions: only one box should be selected.

❌ Common errors

• Mixing up diamond and graphite.
• Saying graphite conducts because of “ions” or “protons” — that is incorrect.
• For methane, drawing too many or too few electrons in overlaps.
• Not giving enough detail for a 2-mark “describe” question.

✅ Correct answer

Draw one shared pair of electrons in each of the three overlaps between the carbon atom and the hydrogen atoms shown.

Accept dots, crosses, circles or any combination, as long as each overlap contains 2 electrons.

💡 Key knowledge

• Carbon has 4 outer-shell electrons.
• Hydrogen has 1 outer-shell electron.
• Methane is CH₄, so carbon makes 4 single covalent bonds.
• In this question, one H is already shown as overlapping in the diagram, and the mark scheme allows the same bonding pattern to be completed across the visible overlaps.

🧠 Exam technique

• The mark scheme rewards the shared pairs, not artistic drawing.
• Place electrons in the overlap to show bonding.
• Ignore inner-shell electrons on carbon.

❌ Common errors

• Putting extra electrons on the outside of carbon or hydrogen.
• Drawing only one electron in an overlap instead of a shared pair.
• Forgetting that each hydrogen can only form one bond.

✅ Correct answer

The third diagram is diamond.

💡 Key knowledge

• Diamond is a giant covalent structure.
• Each carbon atom forms 4 covalent bonds.
• The structure is a 3D lattice, not layers and not a tube.

🧠 Exam technique

• Look for the model where each carbon is bonded in a tetrahedral network.
• In multiple-choice diagram questions, compare the number of bonds per carbon.

❌ Common errors

• Choosing the fullerene sphere or tube.
• Choosing the polymer-like chain structure.
• Confusing diamond with graphite because both contain only carbon.

✅ Correct answer

3

💡 Key knowledge

• Each carbon atom in graphite forms three covalent bonds.
• The fourth outer electron is delocalised.

🧠 Exam technique

• This is a straight recall question: one mark, one word or number.
• Give the exact number: 3.

❌ Common errors

• Answering 4 because carbon has 4 outer electrons.
• Writing “three and a half” or “mostly 3”.

✅ Correct answer

Delocalised electrons

💡 Key knowledge

• Graphite conducts because it has free-moving electrons.
• These electrons can move through the structure and carry charge.

🧠 Exam technique

• “Delocalised electrons” is the safest full-mark answer.
• “Free electrons” is also accepted.

❌ Common errors

• Saying “ions” because graphite is a solid.
• Saying “atoms” carry the charge.
• Thinking the layers themselves carry charge.

✅ Correct answer

In electronic components

💡 Key knowledge

• Fullerenes have uses in electronics.
• They are carbon structures with useful properties for very small-scale applications.

🧠 Exam technique

• Only one box should be ticked.
• Use the exact wording if possible: electronic components.

❌ Common errors

• Choosing self-heating cans or sports injury packs — those are not fullerene uses here.
• Ticking more than one box.

✅ Correct answer

Any two of the following:

• Hollow shape.
• Cylindrical shape / nanotube.
• Made of hexagonal rings.
• Made of carbon atoms.
• Each carbon atom forms 3 covalent bonds.

💡 Key knowledge

• The figure shows a carbon nanotube type fullerene.
• It is a hollow cylinder built from carbon atoms.
• The atoms are joined in hexagonal patterns.

🧠 Exam technique

• For 2 marks, give two separate structural features.
• Good answers are short and precise: “hollow” and “hexagonal rings”.
• If you write “nanotube”, that is accepted as cylindrical/hollow fullerene.

❌ Common errors

• Saying it is a sphere when the image shows a tube.
• Writing “many bonds” without saying 3 bonds per carbon.
• Describing graphite layers instead of a fullerene.

Diamond

Each carbon forms 4 covalent bonds. It is a giant covalent lattice.

Graphite

Each carbon forms 3 covalent bonds and has delocalised electrons, so it conducts electricity.

Fullerenes

They are hollow, often cylindrical, and made of carbon atoms in hexagonal rings.