Giant Ionic Lattice

Summary: The regular three-dimensional arrangement of alternating positive and negative ions that makes up the structure of every ionic compound. Tags: igcse chemistry Created: 2026-07-18

A giant ionic lattice is the structure adopted by all Ionic Compounds: a regular, repeating three-dimensional arrangement of alternating positive and negative ions that extends throughout the entire crystal. It is one type of Giant Lattice (alongside giant covalent and giant metallic structures — see Giant Structures), and the word “giant” signals that the pattern continues indefinitely rather than being limited to a fixed number of atoms as in a Molecule. Each ion is held in place by the strong electrostatic attraction of the Ionic Bond, which acts in all directions between the ion and all of its oppositely charged neighbours, so there is no single “bond” between one pair of ions but rather a network of attractions binding the whole crystal together. The classic example is sodium chloride, in which each Na⁺ ion is surrounded by six Cl⁻ ions and each Cl⁻ ion by six Na⁺ ions. The regularity of the lattice at the particle level is what gives ionic crystals their characteristic cubic shapes, and the strength and arrangement of the attractions explain the physical properties described under Ionic Compounds.

The Sodium Chloride Lattice

Sodium chloride is the standard example of a giant ionic lattice. Its features are:

• Alternation: Na⁺ and Cl⁻ ions alternate in every direction — along rows, up columns, and through layers — so every ion’s nearest neighbours are all of opposite charge.
• 6:6 coordination: each Na⁺ ion is in contact with six Cl⁻ ions (above, below, left, right, in front, behind), and each Cl⁻ ion is likewise surrounded by six Na⁺ ions. The coordination number of both ions is 6.
• Cubic arrangement: the ions sit at the corners and faces of repeating cubes, which is why salt crystals are visibly cubic.
• 1:1 ratio: the lattice contains equal numbers of Na⁺ and Cl⁻ ions overall, so the compound is electrically neutral and its formula is NaCl. The formula describes this ratio, not a molecule.

A two-dimensional slice of the lattice can be pictured as a checkerboard of charges:

   Na⁺  Cl⁻  Na⁺  Cl⁻  Na⁺
   Cl⁻  Na⁺  Cl⁻  Na⁺  Cl⁻
   Na⁺  Cl⁻  Na⁺  Cl⁻  Na⁺
   Cl⁻  Na⁺  Cl⁻  Na⁺  Cl⁻

In three dimensions, identical layers stack so that each Na⁺ sits directly above and below a Cl⁻, completing the six-fold coordination. The Cl⁻ ion is drawn larger than the Na⁺ ion, because negative ions are larger than positive ions formed from atoms in the same period.

Other ionic compounds form analogous lattices; the exact geometry depends on the relative sizes and charges of the ions, but the principle of a regular alternating arrangement of oppositely charged ions is universal.

Why the Lattice Explains the Properties

The giant ionic lattice model accounts for the physical properties of Ionic Compounds:

Charge density also matters: a lattice of doubly charged ions such as MgO (Mg²⁺/O²⁻) is held together far more strongly than NaCl (Na⁺/Cl⁻), giving MgO a much higher melting point (2852 °C versus 801 °C) — high enough for it to be used as a refractory furnace lining.

Comparison with Other Giant Structures

See Giant Lattice and Giant Structures for the covalent and metallic cases.

Sources

• Cambridge IGCSE Chemistry 0620 Syllabus (2023-2025) — Section 2.4 (Supplement 5), Cambridge Assessment International Education

Common Misconceptions