Giant ionic lattice

A giant ionic lattice is a regular three-dimensional arrangement of a very large number of oppositely charged ions, held together by strong electrostatic forces throughout the whole structure. Malay: kekisi ion gergasi · Chinese: 巨型离子晶格.

Because the electrostatic attraction of an ion acts in every direction, an ionic compound does not exist as separate molecules. Instead each cation surrounds itself with anions and each anion with cations, and this pattern repeats over and over to build a giant, orderly structure. The word “giant” means the lattice contains an enormous, unfixed number of ions rather than a small, fixed number of atoms. Every ion is locked in place by strong bonds to all its neighbours, so a great deal of energy is needed to break the structure apart.

Example. Sodium chloride forms a cubic lattice in which each Na⁺ is surrounded by six Cl⁻ ions and each Cl⁻ by six Na⁺ ions, repeating throughout the crystal. This is why a single grain of salt is really one gigantic lattice, and why its formula NaCl gives only the ratio of ions, not the number in the crystal.

Confusion to avoid. Do not describe an ionic compound as being made of molecules, and do not talk about a “sodium chloride molecule”, there is no such thing, only the lattice. Take care to distinguish the giant ionic lattice from a simple molecular structure, which is made of small separate molecules and is held by weak forces.

The giant ionic lattice explains the high melting points, hardness, brittleness and conductivity-when-molten of ionic compounds, so it links directly to the properties compared against simple molecular substances in SPM Chemistry.