Ionic Bonds & Lattice Structure
Section: 2. Atoms, Elements & Compounds | Syllabus: Cambridge IGCSE Chemistry (0620)
The Giant Ionic Lattice
Ionic compounds do not exist as separate pairs of ions or as individual "molecules". Instead, ions pack together into a giant ionic lattice: a regular, repeating three-dimensional arrangement of alternating positive and negative ions, held together by electrostatic attraction acting in every direction.
- The pattern of ions repeats regularly throughout the entire crystal
- Each ion is attracted to several neighbouring ions of opposite charge, not just one
- A single crystal contains a huge number of ions - the chemical formula (e.g. NaCl) shows only the simplest whole-number ratio of ions, not a separate unit
Example: Sodium Chloride Lattice
In solid NaCl, each Na⁺ ion is surrounded by 6 Cl⁻ ions, and each Cl⁻ ion is surrounded by 6 Na⁺ ions, arranged in a repeating cubic pattern.
Each ion in the lattice is surrounded by six oppositely charged neighbours, so the attraction acts throughout the whole structure, not just between one pair of ions
Worked Example: Describing a Lattice
- Question: describe the structure of solid magnesium oxide, MgO. [2]
- Answer: MgO consists of a giant lattice of Mg²⁺ and O²⁻ ions arranged in a regular, repeating pattern [1]; the oppositely charged ions are held together by strong electrostatic forces of attraction acting in all directions [1]
Common Mistakes
- ❌ Thinking the formula NaCl represents one individual molecule
- ✓ NaCl shows the 1:1 ratio of ions in the giant lattice - there is no single "molecule" of an ionic compound, since the whole crystal is one continuous structure
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