Physical Properties of Ionic Compounds

Specification Point 1.33:
  • Explain the properties of ionic compounds limited to:
    a) high melting points and boiling points, in terms of forces
    between ions
    b) whether or not they conduct electricity as solids, when molten and in aqueous solution
  • Ionic substances have high melting and boiling points due to the presence of strong electrostatic forces acting between the oppositely charged ions.
  • Ionic substances can conduct electricity when in either the molten state or when dissolved in solution. In both cases the ions must be able to move and carry the charge.
  • In solid ionic substances the ions are in fixed positions and cannot move, hence they do not conduct electricity.

Conductivity Ionic Substances, Edexcel GCSE Chemistry

Particles in solution/molten form can move and conduct electricity but in solid form they are in fixed positions and are unable to conduct

Physical Properties of Simple Covalent Compounds

Specification Point 1.34:
  • Explain the properties of typical covalent, simple molecular compounds limited to:
    a) low melting points and boiling points, in terms of forces between molecules (intermolecular forces)
    b) poor conduction of electricity
  • Simple covalent compounds have low melting and boiling points as there are only weak intermolecular forces acting between the molecules which must be overcome for melting or boiling to occur
  • They are poor conductors of electricity as there are no free ions or electrons to move and carry charge.
  • Most covalent compounds do not conduct at all in the solid state and are thus insulators.
  • Common insulators include the plastic coating around household electrical wiring, rubber and wood.

Electrical wire insulator, Edexcel GCSE Chemistry

Diagram showing the plastic coating surrounding the conducting metal wires in an electric cable

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.