C2.2 Structure and Properties of Substances


C2.2.1 Simple Molecules

A simple molecule consists of a few atoms joined together by covalent bonds


  • Weak intermolecular forces (attractive forces between molecules)
    • Relatively easy to overcome or break in state changes
  • Strong covalent bonds between atoms
    • Do not break in state changes


  • Relatively low melting and boiling points
  • Tend to be liquids ot gases at room temperature
  • Insulator/poor conductor of electricity
    • Have no overall electric charge
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C2.2.2 Ionic Compounds


  • Regular structures/giant ionic lattices
    • Strong electrostatic forces
      • In all directions
      • Between oppositely charged ions


  • High melting and boiling points 
    • Large amounts of energy needed to break strong ionic bonds
  • Solid at room temperature
  • Can conduct electricity when melted or dissolved in water
    • Charged ions free to move around
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C2.2.3 Macromolecules

Both macromolecules and simple molecules contain convalent bonds

  • General properties
    • Solids at room temperature
    • Very high melting points
      • Atoms linked together by strong covalent bonds
  • Diamond
    • Very hard
      • Each atom bonded to four others with strong covalent bonds
  • Graphite
    • Soft and sliperry, layers slide over each other
      • Each atom bonded to three others with strong covalent bonds between atoms in a layer
      • Weak intermolecular forces and no covalent bonds between layers
    • Conducts heat and electricity
      • Similar to metals as one electron from each carbon atom is delocalised
  • Fullerenes
    • Structure based on hexagonal rings of carbon atoms. 
    • Drug delivery into the body, lubricants, catalysts, nanotubes for reinforcing materials
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C2.2.4 Metals


  • Can be bent and shaped
    • Layers of atoms in the giant lattice can slide over each other
  • Can conduct heat and electricity
    • Have free delocalised electrons in their structures


  • Harder than pure metals
    • Mixture of metals
    • Different sized atoms distort layers
      • More difficult for layers to slide over each other
  • Shape memory alloys
    • Can return to their original shape after being deformed
    • e.g. Nitinol in dental braces
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C2.2.5 Polymers

Large molecules made when small molecules (monomers) join together, e.g. Poly(ethene) and poly(propene)


  • Individual, tangled polymer chains
  • No cross links
  • Soften and melt when heated 
    • Chains slide over each other easily
  • Weak intermolecular forces between chains


  • Polymer chains with cross links between them
  • Do not soften or melt when heated

Properties of polymers depend on monomers used and reaction conditions. LDPE (low density poly(ethene)) and HDPE (high-density poly(ethene)) are made at different temperatures and pressures with different catalysts, so have different properties and uses 

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C2.2.6 Nanoscience

Refers to structures 1-100nm in size (1nm is one millionth of a mm) 


  • Have:
    • Only a few hundred atoms
    • A high surface area to volume ratio
    • Properties different from the same substance in larger pieces
  • Can be used as:
    • Computers, catalysts, coatings
    • Highly selective sensors to detect substances
    • Stronger and lighter construction materials
    • Cosmetics such as sunscreens and deodorants


  • Made of carbon
  • Structure similarnto a graphite layer rolled into a tube
  • Very strong
  • Conduct electricity
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