Properties of Ionic Compounds (Cambridge (CIE) IGCSE Chemistry)

Properties of ionic compounds

• Ionic compounds are usually solid at room temperature 

• They have high melting and boiling points

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

• They are poor conductors in the solid state

Explaining the properties of ionic compounds

Extended tier only

• Ionic compounds have high melting and boiling points

  • 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 

• 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

• 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^-

Diagram to show the electrical conductivity of ionic compounds

Molten or aqueous ions move freely but cannot in solid form