Giant Structures

Giant structures are extended, three-dimensional networks of atoms or ions held together by strong bonds throughout the entire structure. Unlike simple molecular substances, where weak intermolecular forces determine physical properties, the properties of giant structures are governed by the strong bonds within the lattice. This gives them characteristically high melting points and other distinctive properties.

There are two main types: giant ionic lattices and giant covalent structures.

---

Giant Ionic Lattices

We covered ionic bonding in detail in Lesson 1, but here we revisit the structures with a focus on comparing the two key lattice types.

The NaCl Structure

In sodium chloride:

• Coordination number: 6:6 (each ion is surrounded by 6 of the opposite type)
• The ions arrange in a face-centred cubic lattice
• Na⁺ and Cl⁻ alternate at every position

The CsCl Structure

Caesium chloride has a different structure because Cs⁺ is much larger than Na⁺:

• Coordination number: 8:8 (each ion is surrounded by 8 of the opposite type)
• Cs⁺ sits at the centre of a cube of 8 Cl⁻ ions
• The larger Cs⁺ ion can accommodate 8 nearest neighbours (Na⁺ is too small)