A level Chemistry · Edexcel 9CH0 · Topic 2A
Ionic bonding
Key points
- An ionic bond is the strong electrostatic attraction between oppositely charged ions, acting in all directions in a giant lattice.
- Show formation with dot-and-cross diagrams: metals lose electrons to form positive ions, non-metals gain them to form negative ions.
- Bond strength increases with higher ionic charge and smaller ionic radius (greater charge density).
- Ionic radius trends: positive ions are smaller than their atoms; for isoelectronic ions (N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺, Al³⁺) radius falls as nuclear charge rises.
- Evidence for ions: migration of coloured ions in electrolysis (e.g. copper(II) chromate(VI)) and electron density maps.
- Properties: high melting points, conduct when molten or dissolved (ions free to move), not when solid; often soluble in water; brittle.
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Ionic bonding is the strong electrostatic attraction between oppositely charged ions in a lattice. Its strength depends on the charges and sizes of the ions, and in real compounds it is often not "purely" ionic.
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