High melting points, brittle crystals, and conduction when molten or dissolved.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Strong electrostatic forces in the lattice give ionic compounds high melting and boiling points and make them hard. They are brittle because shifting one layer of ions brings like charges adjacent, causing repulsion and cleavage along a plane. In the solid state the ions are fixed in place, so the solid does not conduct electricity. When melted or dissolved in a polar solvent, the ions become mobile and carry charge. Most ionic salts dissolve readily in water, where the solvent stabilizes the separated ions.
Key ideas: Use the properties as a diagnostic: high melting point, brittle, conducting only when molten or dissolved, and often soluble in water. Predict relative melting points with lattice energy: MgO melts at 2852 C while NaCl melts at 801 C. Electrolysis of melts is a consequence of mobile ions.
Common mistakes and connections: Students think solid salts conduct because they contain charged ions, but the ions cannot move. Another error is assuming all ionic compounds dissolve in water (AgCl, BaSO4 and CaCO3 do not). Also brittleness is not weakness: ionic crystals are hard but shatter. Connects to lattice energy, solubility rules, electrolysis and conductivity.
Strong electrostatic lattices give high melting points, rising sharply when ions carry higher charges, as in MgO. The interactive lesson shows this as a live animation or chart.
Solid sodium chloride is an electrical insulator, but molten sodium chloride conducts electricity readily.
High melting points, brittle crystals, and conduction when molten or dissolved.
Properties of Ionic Compounds is a beginner topic in Bonding & Molecular Structure. It needs no earlier chemistry lessons and is a good starting point.
Study these earlier topics in Bonding & Molecular Structure first: Polarizability, Lattice Energy, Born-Haber Cycle.
The next topics in Bonding & Molecular Structure are Properties of Covalent Compounds and Properties of Metals.
Yes. The interactive lesson includes a self-check question on Properties of Ionic Compounds, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Properties of Ionic Compounds is topic 29 of 104 in Bonding & Molecular Structure.