Properties of Ionic Compounds
Syllabus 2.4.4 & 2.4.7 | The Electrifying Truth
The Ionic Paradox
Salt conducts electricity when molten or dissolved in water, but NOT when solid. Why? Because conductivity requires MOBILE CHARGED PARTICLES.
Experiment 1: The Conductivity Test
Ions are LOCKED in a rigid lattice. They can only vibrate in place.
Bulb Off
🔬 The Science Behind It
Solid State: Ions are held rigidly in the lattice by strong electrostatic forces. They can only vibrate, so they cannot carry charge. No conductivity.
Molten/Aqueous: The lattice breaks down. Ions become mobile charge carriers. They migrate to oppositely charged electrodes. Conducts electricity!
Experiment 2: The Melting Point Challenge
Sodium Chloride (NaCl)
Melting Point: 801°C
Bond Type: Ionic (Strong)
❄️ Solid
🔬 Why Such Different Melting Points?
Salt (Ionic): Strong electrostatic forces between oppositely charged ions (Na⁺ and Cl⁻) throughout the entire giant lattice. Breaking these requires ENORMOUS energy → MP: 801°C
Sugar (Covalent): Strong covalent bonds WITHIN molecules, but only weak intermolecular forces BETWEEN molecules. Breaking these weak forces requires little energy → MP: 186°C
⚡ Key Insight: High melting points indicate strong forces holding the structure together. Ionic compounds have some of the highest melting points in chemistry!
📋 Summary: Properties of Ionic Compounds
High Melting & Boiling Points
- •Strong electrostatic forces between ions
- •Giant lattice structure throughout
- •Requires large amount of heat energy to overcome
Electrical Conductivity
- ✗Solid: Poor conductor (ions fixed in lattice)
- ✓Molten: Good conductor (ions mobile)
- ✓Aqueous: Good conductor (ions dispersed in water)
⚠️ EXAMINER TRAP
Students often say "ionic compounds conduct electricity." This is WRONG! You must specify: "Ionic compounds conduct electricity when molten or in aqueous solutionbecause the ions are free to move and carry charge."
🎯 KEY TERMS FOR EXAMS
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