Ionic Compounds and Their Properties

This lesson covers the structure and properties of ionic compounds, as required by the AQA GCSE Chemistry specification (4.2.1). You need to understand what an ionic lattice is, why ionic compounds have high melting and boiling points, and why they can conduct electricity when molten or dissolved but not when solid.

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The Ionic Lattice

Ionic compounds do not exist as individual pairs of ions. Instead, the ions are arranged in a regular, repeating three-dimensional pattern called a giant ionic lattice. In this lattice, every positive ion is surrounded by negative ions, and every negative ion is surrounded by positive ions. The strong electrostatic forces of attraction act in all directions — this is what makes the structure so stable.

The term giant means that the lattice extends in all three dimensions and contains billions upon billions of ions. There are no individual molecules in an ionic compound — the formula (e.g. NaCl) simply represents the ratio of ions present.