AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Higher), 2020: Question 2

✅ Correct answer

Any one of these:

• It is not to scale.
• It is not 3-dimensional.
• It shows the wrong arrangement in space.
• Electrons / shells are not shown.

💡 Key knowledge

• Models are simplified versions of real particles.
• The ball-and-stick model helps show shape, but it does not show true size or full structure.
• For water, the actual molecule is not drawn as a physical “stick” structure in real life.

🧠 Exam technique

• Give one clear limitation only — no need for a long explanation.
• Use exact phrases like not to scale or not 3D .
• If you write “it is inaccurate,” make sure you say how it is inaccurate.

❌ Common errors

• Saying the model shows “the properties of water” — this was not what the question asked.
• Writing vague answers like “it is wrong” with no detail.
• Talking about the bonds being “weak” here — that relates to a different part of the question.

✅ Correct answer

Weak.

💡 Key knowledge

• In ice, water molecules are held together by intermolecular forces.
• These forces are much weaker than the covalent bonds inside molecules.
• Because they are weak, less energy is needed to overcome them, so ice melts at a low temperature.

🧠 Exam technique

• The blank is asking for a single adjective.
• Learn the exact sentence: “intermolecular forces are weak.”

❌ Common errors

• Writing “strong” — that is the opposite of the mark scheme.
• Explaining covalent bonds instead of intermolecular forces.
• Writing “weak bonds” can sometimes be accepted informally, but the safest answer is weak forces.

✅ Correct answer

CH₄O

Also accepted: CH₃OH

💡 Key knowledge

• Count the atoms shown in the model.
• There is 1 carbon, 4 hydrogen, and 1 oxygen.
• That gives CH₄O .

🧠 Exam technique

• Count each atom carefully from the labelled model.
• Order is usually C, H, then other elements.
• If you write the displayed alcohol form, CH₃OH , that is also fine.

❌ Common errors

• Missing one hydrogen atom.
• Writing the structural formula with incorrect atom counts.
• Confusing the labels and counting the wrong ball as carbon or oxygen.

✅ Correct answer

4

💡 Key knowledge

• In diamond, each carbon atom forms four covalent bonds.
• This gives a strong giant covalent structure.
• Each carbon is bonded to four other carbon atoms in a tetrahedral arrangement.

🧠 Exam technique

• If it is a tick-box question, choose only the number that matches the key fact.
• Remember: diamond = 4 bonds per carbon.

❌ Common errors

• Choosing 2 or 3 because of confusing diamond with other structures.
• Thinking each carbon only makes one bond because the picture shows one visible line.

✅ Correct answers

Any two from:

• (Very) hard / strong
• (Very) high melting point
• Does not conduct electricity

💡 Key knowledge

• Diamond has a giant covalent structure with many strong covalent bonds.
• Strong bonds throughout the structure make it hard and give it a very high melting point.
• Diamond does not conduct electricity because it has no free electrons.

🧠 Exam technique

• Choose two different properties to secure both marks.
• “Hard” is the most common correct choice.
• If you give “does not conduct electricity,” that is also a strong exam answer.

❌ Common errors

• Writing “shiny” — this was ignored in the mark scheme.
• Giving only one property twice in different words.
• Saying diamond conducts electricity because it has bonded electrons.

✅ Correct answers

Any two from:

• Graphite / graphene
• Silicon dioxide / silica
• Silicon
• Polymers / named polymers
• Fullerene / carbon nanotubes

💡 Key knowledge

• Giant covalent structures are networks of atoms joined by many covalent bonds.
• Common GCSE examples include graphite and silicon dioxide.
• Graphene and carbon nanotubes are also accepted examples.

🧠 Exam technique

• Write two clearly different examples.
• Safer choices: graphite and silicon dioxide.
• Check spelling enough for the examiner to recognise the substance.

❌ Common errors

• Writing a substance that is not giant covalent.
• Repeating the same answer in different forms, e.g. “graphite” and “graphene” if your teacher has not covered both as separate examples — though both were allowed here.
• Giving a property instead of a substance.

💡 What top answers did well

• Used exact scientific wording: weak, not to scale, 4 bonds.
• Kept answers short and direct.
• Gave two valid examples when asked for two marks.

🧠 How marks were awarded

• Most parts were 1-mark recall points.
• These questions reward specific keywords, not long explanations.
• If a question asks for a number, a property, or a named substance, answer exactly that.

❌ Main traps

• Mixing up intermolecular forces with covalent bonds.
• Confusing the structure of diamond with graphite.
• Writing vague model limitations instead of one precise limitation.