Cognito · AQA ChemistryIonic bonding and giant ionic lattices
Key facts
Formation of ions and ionic bonds
Ions form when atoms gain or lose electrons to achieve a full outer shell.
Metals lose electrons → form positive ions (cations). E.g. Na → Na⁺ + e⁻.
Non-metals gain electrons → form negative ions (anions). E.g. Cl + e⁻ → Cl⁻.
Ionic bond = electrostatic attraction between oppositely charged ions.
Dot-and-cross diagrams show electron transfer between atoms.
Common ions to know: Na⁺, K⁺, Ca²⁺, Mg²⁺, Al³⁺, Cl⁻, O²⁻, N³⁻, SO₄²⁻, NO₃⁻, OH⁻, CO₃²⁻.
Properties of ionic compounds
Giant ionic lattice — millions of ions arranged in regular repeating 3D structure.
High melting/boiling points — strong electrostatic forces between many ions require lots of energy to break.
Conduct electricity when molten or dissolved — ions are free to move and carry charge.
Do NOT conduct when solid — ions are fixed in lattice positions.
Often soluble in water — water molecules attract and separate the ions.
Exam questions — 3 questions · 9 marks
⚡ Extended questions included. Read the hint. Show all working. AI marks against the real AQA mark scheme.
1 markIon formationAQA 8462 P1 style
Magnesium (atomic number 12) reacts with oxygen (atomic number 8) to form magnesium oxide. What ions are formed?
A Mg⁻ and O²⁺
B Mg²⁺ and O²⁻
C Mg⁺ and O⁻
D Mg²⁺ and O²⁺
1 markElectrical conductivityAQA 8462 P1 style
Why does solid sodium chloride not conduct electricity but molten sodium chloride does?
A Solid NaCl has no ions; molten NaCl forms ions when it melts
B In solid NaCl the ions are fixed in position and cannot move; in molten NaCl the ions are free to move and carry charge
C Solid NaCl is an insulator because it contains covalent bonds
D Molten NaCl conducts because it has free electrons
4 marksDescribe ionic structure and propertiesAQA 8462 P1 style
Describe the structure of a giant ionic lattice and use it to explain why ionic compounds have high melting points and can conduct electricity when dissolved in water. (4 marks)
Hint: Cover: lattice structure → strong forces → high melting point. Then: dissolved → ions free to move → conduction.
+40 XP
3 marksDot and cross diagram descriptionAQA 8462 P1 style
Describe what a dot-and-cross diagram for the ionic compound magnesium chloride (MgCl₂) would show. Explain why two chlorine atoms are needed for each magnesium atom. (3 marks)
Hint: Mg has 2 outer electrons — needs to lose both. Each Cl needs 1 electron — so 2 Cl atoms needed. Show the electron transfer.