Chemistry · Bonding, Structure and Properties of Matter
Structure and Properties of Ionic Compounds
Spec 5.2.2.3📙 Higher
Theory · read, then commit
Ionic compounds have a giant ionic lattice with strong electrostatic forces in all directions between alternating positive and negative ions. That one structure explains every property. The formula shows the simplest whole-number ratio of ions.
🧂NaCl (charges ±1)
Ion chargesNa⁺ and Cl⁻
Force strengthStrong
Melting point801 °C
🧲MgO (charges ±2)
Ion chargesMg²⁺ and O²⁻
Force strengthMuch stronger (double charges)
Melting point2852 °C
Higher ion charges → stronger attraction → higher melting point. That is why MgO melts far above NaCl.
Checkpoint · quick check
Describe the type of structure that is responsible for the properties of ionic compounds.
Properties of ionic compounds
💥Hard but brittle
A force shifts the layers so like charges align and repel — the crystal shatters rather than bending.
🚫No conduction when solid
Ions are fixed in the lattice, so nothing can carry charge.
⚡Conducts molten or dissolved
The ions become free to move and carry the current.
Checkpoint · quick check
Explain why ionic compounds conduct electricity when molten or dissolved, but not when solid.
⚠️ Common Mistake
Students often say that ionic solutions conduct electricity because electrons flow through them, just like in a metal. They do not: ionic compounds have no free electrons. They conduct only when molten or dissolved, and it is the ions themselves that move and carry the charge. (This is also why ionic compounds are brittle rather than bendy — shifting the lattice brings like charges together, and they repel.)
Retrieval · sort the cards
Test yourself · 10 questions, exam order
0 of 10 answered
Warm-up · 3 questions
A student tests whether sodium chloride conducts electricity in four forms: solid, dissolved in water, molten, and as a vapour. Predict in which forms it conducts, and explain why.
Explain why ionic compounds have high melting and boiling points.
Ionic compounds are hard but brittle. Explain why a crystal shatters when it is struck.
Exam standard · 3 questions
Magnesium oxide (MgO) has a higher melting point than sodium chloride (NaCl). Explain why.
Explain the difference between how a metal conducts electricity and how molten sodium chloride conducts electricity.
Predict which has the higher melting point, sodium chloride (NaCl) or sodium oxide (Na₂O), and justify your answer using ionic charge.
Stretch · 4 questions
Explain why the melting point of an ionic compound gives information about the strength of the forces between its ions.
Suggest why magnesium oxide is used to line the inside of furnaces.
Aluminium oxide (Al₂O₃) has a very high melting point. Explain, in terms of ionic charge, why it is higher than that of sodium chloride.
Explain why the ability of a molten ionic compound to conduct electricity depends on its ions acting as charge carriers.
Key note · cover it, say it, check it
Revision card · 6 stepsStructure and Properties of Ionic Compounds
01Giant ionic lattice → high MP/BP (strong electrostatic forces).