AQA GCSE Combined Science: Trilogy Chemistry Paper 1 (Higher), 2018: Question 5

✅ The core ideas

• Diamond is a giant covalent structure.
• Sodium chloride only conducts when ions can move.
• Sodium conducts thermal energy using delocalised electrons.

🧠 How marks are awarded

• Each part is worth 3 marks.
• Usually you need three linked statements for full marks.
• Use the exact particle type: bonds, ions, electrons, or structure.

❌ Common traps

• Saying “heat makes it melt” without explaining the strong bonds.
• Saying NaCl conducts as a solid.
• Talking about electrical conduction when the question asks about thermal energy.

✅ Correct answer

Diamond has a giant covalent structure made of atoms joined by covalent bonds. There are lots of strong bonds throughout the structure, so a lot of energy is needed to break/overcome them before diamond can melt.

💡 Key knowledge

• Diamond is a macromolecule / giant covalent lattice.
• Each carbon atom forms 4 covalent bonds.
• Melting requires breaking many strong covalent bonds, not just separating molecules.

🧠 Exam technique

• To score full marks, link structure → bonds → energy.
• A safe 3-mark chain is:
  giant covalent structure → strong covalent bonds → lots of energy needed to break them
• “Strong bonds” alone can gain a mark if the rest is missing, but full marks need the full explanation.

❌ Common errors

• “Diamond has strong particles” — too vague.
• “It has strong intermolecular forces” — incorrect for diamond.
• Talking about “many atoms” without explaining covalent bonds.
• Using the word lattice is fine, but it does not replace the need to mention strong covalent bonds.

✅ Correct answer

Sodium chloride conducts electricity when it is molten or dissolved in water (aqueous / in solution), because the ions are free to move and carry charge.

💡 Key knowledge

• In a solid, ions are fixed in a lattice and cannot move.
• When molten or dissolved, the ionic lattice breaks apart enough for ions to move.
• It is the movement of ions that allows current to flow.

🧠 Exam technique

• Use the phrase “free / mobile ions”.
• Give both condition and reason:
  molten or aqueous + ions can move
• If you only say “it has ions”, that is not enough for the movement mark.

❌ Common errors

• Saying it conducts as a solid.
• Saying electrons carry the charge in NaCl — not for this GCSE model.
• Missing the condition and only writing “ions move”.
• Using “dissolved” without saying in water / aqueous / solution can lose precision.

✅ Correct answer

Sodium has delocalised electrons from the outer shell that are free to move through the metal. When one part is heated, these electrons gain energy and move through the structure, transferring energy to other ions/atoms by collisions.

💡 Key knowledge

• Metals contain positive ions in a lattice and delocalised electrons.
• Thermal energy is transferred quickly by moving electrons through the structure.
• In GCSE answers, “ions/atoms vibrate” can gain limited credit if the main idea is missing.

🧠 Exam technique

• Focus on thermal energy, not electrical conduction.
• Use the sequence:
  delocalised electrons → move → transfer energy through the structure
• Do not forget that the electrons come from the outer shell.

❌ Common errors

• Saying “heat rises” — not a particle explanation.
• Talking only about atoms vibrating without mentioning electrons.
• Writing “electrons carry electricity” when the question asks for thermal energy.
• Mixing up metals with ionic structures.

Diamond

Giant covalent structure with strong covalent bonds throughout, so lots of energy is needed to break the structure.

Sodium chloride

Only conducts when molten or aqueous because ions are free to move and carry charge.

Sodium

Conducts thermal energy because delocalised electrons move through the metal and transfer energy.

✅ Use precise science words

• covalent bonds
• giant covalent structure
• molten / aqueous
• free / mobile ions
• delocalised electrons

❌ Avoid vague phrases

• “It is strong” without saying what is strong.
• “It melts because of heat” without explaining bonds.
• “It conducts because of particles” without naming ions/electrons.