Giant ionic lattice: e.g. NaCl. Alternating + and − ions. High melting point. Conducts electricity when molten or dissolved (ions free to move). Brittle.
Giant covalent structure: e.g. diamond, graphite, silicon dioxide. Very high melting point. Usually do not conduct electricity (no charged particles). Very hard (diamond).
Giant metallic structure: positive metal ions in a lattice of delocalised electrons. Good conductor of electricity (electrons free to move). Malleable (layers can slide).
Simple molecular vs giant structures
Simple molecular: e.g. H₂O, CO₂, CH₄. Low melting/boiling points (weak intermolecular forces). Do not conduct electricity.
Larger molecules have higher boiling points (stronger intermolecular forces).
Ionic structures have the highest melting points, then giant covalent, then metallic, then simple molecular.
Solubility: ionic compounds often dissolve in water. Giant covalent structures generally do not.
⚡ Show all working — the AI marks against the AQA mark scheme. Method marks awarded for correct working even if the final answer is wrong.
1 markState descriptionAQA 8462 style
Which statement correctly describes the particles in a liquid?
A Particles are in a fixed, regular arrangement with no movement
B Particles are close together, randomly arranged, and able to move past each other
C Particles are far apart and move randomly at high speed
D Particles are in a regular lattice with strong fixed bonds
3 marksExplain high melting pointAQA 8462 P1 style
Sodium chloride has a melting point of 801°C. Explain this in terms of its structure and bonding. (3 marks)
Hint: Name the structure (giant ionic lattice), describe the forces between ions (electrostatic attractions), and explain why lots of energy is needed.
+30 XP
1 markElectrical conductivityAQA 8462 style
Sodium chloride does NOT conduct electricity when solid but DOES conduct when molten. Explain why.
A When solid the ions are bonded; when molten the bonds break and electrons are released
B When solid the ions are in fixed positions; when molten they are free to move and carry charge
C Melting changes NaCl into a metal which conducts electricity
D Solid NaCl has too high a resistance; molten NaCl has lower resistance
3 marksCompare structuresAQA 8462 style
Explain why diamond has a very high melting point but methane (CH₄) has a very low boiling point, even though both contain only covalent bonds. (3 marks)
Hint: Key distinction: diamond has GIANT covalent structure (break actual covalent bonds to melt). Methane has simple molecular structure (only weak forces between molecules broken on boiling).