1.4.3 Lattice Structures

• Most ionic, metallic and covalent compounds are crystalline lattice
• The ions, atoms or molecules are arranged in a regular and repeating arrangement

Giant ionic lattices

• An ionic bond is an electrostatic force between a positively charged metal (cation) ion and a negatively charged non-metal (anion) ion
  • The metal becomes positively charged as it transfers electrons to the non-metal becomes negatively charged

• Ionic compounds are arranged in giant ionic lattices (also called giant ionic structures)
• The type of lattice formed depends on the sizes of the positive and negative ions which are arranged in an alternating fashion
  • The ionic lattice of MgO and NaCl are cubic

Ionic lattices of the ionic compounds NaCl and MgO

General ionic lattice which shown the actual packing of the ions

Covalent lattices

• Covalent bonds are bonds between nonmetals in which electrons are shared between the atoms
• Covalent compounds can be arranged in simple molecular or giant molecular lattices
  • Simple molecular lattices: Iodine, buckminsterfullerene (C₆₀) and ice
  • Giant molecular: silicon(IV) oxide, graphite and diamond

Simple molecular lattices

Giant molecular lattices

Metallic lattices

• Metals form giant metallic lattices in which the metal ions are surrounded by a ‘sea’ of delocalised electrons
• The metal ions are often packed in hexagonal layers or in a cubic arrangement

Layers of copper ions (the delocalised electrons are not shown in the diagram)