Properties of Ionic Compounds (Cambridge International IGCSE Chemistry)

Spec point — 2.2.3 · Describe the properties of ionic compounds: high melting points and boiling points; good electrical conductivity when aqueous or molten and poor when solid

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

Spec point — 2.2.3 · Explain in terms of structure and bonding the properties of ionic compounds: high melting points and boiling points; good electrical conductivity when aqueous or molten and poor when solid

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