Properties of Ionic Compounds (AQA GCSE Combined Science: Trilogy): Revision Note Exam code: 8464

Properties of Ionic Compounds (AQA GCSE Combined Science: Trilogy): Revision Note

Exam code: 8464

Properties of ionic compounds

  • Ionic compounds are made of charged particles called ions which form a giant lattice structure 

  • Ionic compounds have high melting and boiling points because:

    • They have giant structures

    • There are strong electrostatic forces of attraction between oppositely charged ions in all directions

    • The forces need lots of energy to overcome them 

  • The greater the charge on the ions, the stronger the electrostatic forces and the higher the melting point will be

    • For example, magnesium oxide consists of Mg2+ and O2- so will have a higher melting point than sodium chloride which contains the ions, Na+ and Cl-

Giant Ionic Lattice of Sodium Chloride

The structure of an ionic compound

Strong electrostatic forces act in all directions in an ionic solid such as sodium chloride

Examiner Tips and Tricks

Ions with higher charge have stronger electrostatic forces and will thus have higher melting and boiling points.

When can ionic compounds conduct electricity?

  • For electrical current to flow there must be freely moving charged particles such as electrons or ions present 

  • Ionic compounds are poor conductors in the solid state

    • The ions are in fixed positions in the lattice

    • They are therefore unable to move and carry a charge 

  • Ionic compounds are good conductors of electricity in the molten state or in solution 

    • When the ionic compound is melted or dissolved in water, the ions are able to move and carry a charge

Diagram to show the electrical conductivity of ionic compounds

Diagram to show why ionic compounds conduct electricity when molten but not when solid

The ions can move when the compound is molten or in solution but can't when the compound is solid

Examiner Tips and Tricks

A common mistake students make is to say that ionic compounds conduct when molten or in solution because 'electrons can move and carry a charge.' You must say that it is due to 'ions' moving and carrying a charge. 


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