Ionic Compounds: Bonds, Structure & Properties (Edexcel IGCSE Science (Double Award) (Modular)): Revision Note

Ionic bonding

• 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 

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

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 O^2- 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 or aqueous particles move and conduct electricity but cannot in the solid state