Knowledge Organiser: Ionic Compounds
Key Terms
- Giant ionic lattice: regular 3D arrangement of alternating ions
- Electrostatic attraction: force between opposite charges
- Electrolyte: conducts electricity when dissolved/molten
- Brittle: shatters when force applied (layer shift → repulsion)
Must-Know Facts
- No molecules — giant lattice structure
- High MP/BP — many strong electrostatic forces
- Solid: NO conduction (ions fixed)
- Molten/dissolved: CONDUCTS (ions free to move)
- Higher charge → stronger forces → higher MP
- MgO melts at 2852°C vs NaCl at 801°C
Key Equations
- No calculation equations — focus on structure and properties
- Conduction requires free ions: solid (no) → molten/dissolved (yes)
- Higher ion charge = stronger electrostatic attraction = higher melting point
Common Mistakes
- Saying ionic compounds conduct electricity when solid: Ions are fixed in the lattice when solid — only molten or dissolved ionic compounds conduct
- Forgetting to explain WHY melting point is high: Say "many strong electrostatic forces between oppositely charged ions require a lot of energy to break"
- Saying ionic compounds are made of molecules: Ionic compounds form giant lattices — there are no discrete molecules
- Not linking ion charge to melting point: MgO has higher charge ions (Mg²⁺, O²⁻) than NaCl (Na⁺, Cl⁻) so has much stronger forces and a higher melting point
Memory Aid
- Solid ionic compound — ions are stuck in the lattice → NO conduction
- Molten (liquid) ionic compound — lattice gone, ions loose → CONDUCTS
- Dissolved in solution — ions swimming freely → CONDUCTS