Ionic Bonds & Lattice Structure (Cambridge International IGCSE Science)

The lattice structure of ionic compounds

Spec point — Describe the giant lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions

Extended Tier Only

Lattice structure

• Ionic compounds have a giant lattice structure
• Lattice structure refers to the arrangement of the atoms of a substance in 3D space
• In lattice structures, the atoms are arranged in an ordered and repeating fashion
• The lattices formed by ionic compounds consist of a regular arrangement of alternating positive and negative ions

The lattice structure of NaCl

Ionic bonds between metallic & non-metallic elements

Spec point — C3.4.3 · Describe the formation of ionic bonds between ions of metallic and non-metallic elements, including the use of dot-and-cross diagrams

Extended Tier Only

Ionic compounds

• Ionic compounds are formed when metal atoms and non-metal atoms react
• The ionic compound has no overall charge

Example: magnesium Oxide, MgO

• Magnesium is a Group II metal so will lose two outer electrons to another atom to have a full outer shell of electrons

• A positive ion with the charge 2+ is formed

• Oxygen is a Group VI non-metal so will need to gain two electrons to have a full outer shell of electrons

• Two electrons will be transferred from the outer shell of the magnesium atom to the outer shell of the oxygen atom

• Oxygen atom will gain two electrons to form a negative ion with charge 2-

• Magnesium oxide has no overall charge

  • MgO

Diagram showing the dot-and-cross diagram of magnesium oxide

Exam Hint When drawing dot and cross diagrams, you only need to show the outer shell of electrons. Remember to draw square brackets and include a charge for each ion. Make sure the overall charge is 0; you may need to include more than one positive or negative ion to ensure the positive and negative charges cancel each other out.