O LevelChemistryCambridge (CIE)Revision Notes2. Atoms, Elements & Compounds2.4 Ions & Ionic BondsIonic Bonds & Lattice Structure

Ionic Bonds & Lattice Structure (Cambridge (CIE) O Level Chemistry): Revision Note

Exam code: 5070

Written by: Alexandra Brennan

Reviewed by: Caroline Carroll

Updated on 13 October 2026

The Lattice Structure of Ionic Compounds

Lattice structure

Ionic compounds have a giant lattice structure
Lattice structure refers to the arrangement of the particles of a substance in 3D space
In an ionic lattice, the ions 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

Two representations of the sodium chloride lattice side by side. On the left an open ball-and-stick cube shows sodium and chloride ions alternating along every edge. On the right a space-filling model shows the same lattice with the larger chloride ions packed around the smaller sodium ions. A key identifies the small red spheres as Na+ and the large green spheres as Cl-.

The lattice structure of NaCl

Ionic Bonds between Metallic & Non-Metallic Elements

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

Dot-and-cross diagram for magnesium oxide. The magnesium ion is drawn inside square brackets with a 2+ charge and eight outer-shell electrons shown as dots. The oxide ion is drawn inside square brackets with a 2- charge and eight outer-shell electrons, six shown as crosses and two as dots to mark the pair transferred from magnesium.

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

Explanation

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

Formula of ionic compound: MgO

Examiner Tips and Tricks

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.

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