Lattice

In IGCSE chemistry, a lattice is a regular, repeating three-dimensional arrangement of particles (atoms, ions, or molecules) forming a crystalline solid ¹.

Giant Ionic Lattice (NaCl):
   [Na+] --- [Cl-] --- [Na+]
     |         |         |
   [Cl-] --- [Na+] --- [Cl-]

Primary Lattice Types

IGCSE categorizes four solid lattice structures ¹:

1. Giant Ionic (e.g., $\text{NaCl}$, $\text{MgO}$):

   • Alternating cations and anions held by strong electrostatic forces.
   • High melting points; conducts electricity when molten or dissolved.

2. Giant Covalent (e.g., diamond, graphite, $\text{SiO}_2$):

   • Giant networks of continuous covalent bonds.
   • Very high melting points; non-conductors (except graphite with delocalized electrons).

3. Giant Metallic (e.g., copper, iron):

   • Regular layers of metal cations in a sea of delocalized electrons.
   • Malleable, ductile, and thermally/electrically conductive.

4. Simple Molecular (e.g., ice, solid $\text{I}_2$):

   • Small molecules arranged regularly, held by weak intermolecular forces.
   • Low melting points.

    Ionic               Metallic            Covalent
 [+] [-] [+]        (+)  (+)  (+)            C - C - C
 [-] [+] [-]        ~ e-  ~ e-  ~             \ /   \
(Ionic bonds)     (Electron "sea")       (Covalent network)

Related

• Freezing - Liquid particles lock into a fixed lattice.
• Melting - Thermal energy breaks down the rigid lattice.
• Pure Substance - Uniform species forming crystal lattices.
• State of Matter - Solid state defined by fixed lattice positions.
• Chemistry - Core science domain.