Ionic Compounds: Bonds, Structure & Properties (Edexcel IGCSE Chemistry (Modular))

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Ionic bonding

  • An ionic compounds consists of a regular arrangement of alternating positive and negative ions in which the ions are tightly packed together

  • Between positive and negative ions are strong electrostatic forces of attraction which act in all directions

  • These are what hold the ionic compound together 

Oppositely charged ions attraction due to electrostatic attraction, IGCSE & GCSE Chemistry revision notes

Electrostatic forces of attraction exist between the oppositely charged ions

Ionic lattices

  • Thousands of positive and negative ions in an ionic compound form a giant lattice structure

  • Compounds with giant ionic lattice have high melting points 

Giant ionic lattice of sodium chloride

NaCl Lattice_ Ball + Ball & Stick, IGCSE & GCSE Chemistry revision notes

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

  • Ionic compounds have high melting and boiling points because:

    • They have giant ionic lattices

    • 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-

Conductivity of ionic compounds

  • 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

Molten ionic substances conduct electricity, IGCSE & GCSE Chemistry revision notes

Molten or aqueous particles move and conduct electricity but cannot in the solid state

Examiner Tip

A common mistake students make in exams is to say that ionic compounds conduct electricity because 'electrons' move and carry a charge, when they should say the ions can move and carry a charge. Don't make that mistake!

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