4.2.1—Describe, in simple terms, the lattice

A crystalline lattice is a regular, repeating arrangement of particles. Classify the lattice by asking what repeats: ions in a giant ionic lattice, atoms in a giant covalent or metallic lattice, or discrete molecules in a simple molecular lattice.

In a giant ionic lattice, oppositely charged ions alternate through the structure and are held by electrostatic attraction in all directions. The arrangement and relative ion sizes determine the packing; sodium chloride and magnesium oxide are source-supported examples of cubic ionic lattices.

Covalent substances may form simple molecular lattices, such as iodine, buckminsterfullerene and ice, where discrete molecules are arranged together, or giant molecular lattices, such as diamond, graphite and silicon(IV) oxide, where covalent bonding extends through a large network. Do not treat all covalent substances as one lattice type.

A giant metallic lattice contains positive metal ions arranged regularly and surrounded by a sea of delocalised electrons. The ions may form layered or cubic arrangements; copper is a source-supported example. The delocalised electrons are part of the metallic structure, not separate molecules between the ions.