Properties of Simple Molecular Compounds (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

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Properties of simple molecular compounds

  • Small molecules are compounds made up of molecules that contain just a few atoms covalently bonded together
  • They have low melting and boiling points so covalent compounds are usually liquids or gases at room temperature
  • As the molecules increase in size, the melting and boiling points generally increase
  • Small molecules have poor electrical conductivity

Explaining the properties of simple molecular compounds

Extended tier only

Linking bonding and properties

  • Small molecules have covalent bonds joining the atoms together, but intermolecular forces that act between neighbouring molecules
  • They have low melting and boiling points as there are only weak intermolecular forces acting between the molecules
  • These forces are very weak when compared to the covalent bonds and so most small molecules are either gases or liquids at room temperature
  • As the molecules increase in size the intermolecular forces also increase as there are more electrons available
  • This causes the melting and boiling points to increase

Intermolecular Forces Vs Covalent Bonds, downloadable IGCSE & GCSE Chemistry revision notes

The bonds between hydrogen and oxygen in water are COVALENT, and the attractions between the molecules are INTERMOLECULAR FORCES which are about one tenth as strong as covalent bonds

Electrical Conductivity

  • Molecular compounds are poor conductors of electricity as there are no free ions or electrons to carry the 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, IGCSE & GCSE Chemistry revision notes

The plastic coating around electrical wires is made from covalent molecules that do not allow a flow of charge

Examiner Tip

The atoms within covalent molecules are held together by covalent bonds while the molecules in a covalent substance are attracted to each other by intermolecular forces.

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Caroline

Author: Caroline

Expertise: Physics Lead

Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.