Covalent substances: Giant Covalent

Covalent substances: Giant Covalent

  • These are similar to giant ionic structures – but no charged ions
  • All the atoms are bonded to each other by strong covalent bonds
  • This means they have very high melting and boiling points
  • They don’t conduct electricity – except for granite
  • The main examples are diamond and graphite – which are made from carbon atoms and silicon dioxide


  • Each carbon atom forms four covalent bonds in a very rigid giant covalent structure
  • This structure makes the diamond the hardest natural substance


  • Each carbon atom forms three covalent bonds- this creates layers which are free to slide over each other – this makes the graphite soft and slippery
  • The layers are held together so weakly that they can be rubbed off onto paper – this is because of the weak intermolecular forces between the layers
  • Graphite is the only non-metal which is a good conductor of heat and electricity – each carbon atom has one delocalised free electron and these free electrons conduct heat and electricity

Silicon Dioxide

  • What sand is made from
  • Each grain of sand is one giant structure of silicon and oxygen


Metallic Structures

Metal Properties are all due to the sea of free electrons

  • Metals also consist of a giant structure
  • Metallic bonds involve the all-important ‘free electrons’ which produce all the properties of metals. These delocalised electrons come from the outer shell of every metal atom in the structure
  • These electrons are free to move through the whole structure and so metals are good conductors of heat and electricity
  • These electrons also hold the atoms together in a regular structure – there are strong forces of electrostatic attraction between the positive metal ions and the negative electrons
  • They also allow the layers of atoms to slide over each other allowing metals to be bent and shaped
  • Alloys are harder than pure metals – this is a mix of two or more metals together, creating the properties that they want
  • Different elements have different sized atoms – when they are mixed the new atoms will distort the layers of metal atoms – this making it more difficult for them to slide over each other – alloys are harder

New Materials

  • Smart materials have some really weird properties
    • Smart materials behave differently depending on the conditions
    • g. ‘Nitinol’ – a shape memory alloy – It’s a metal alloy (half nickel half titanium) that when cool can be bended and twisted like rubber. But when heated it goes back to a remembered shape. – This is useful for glasses frames because if you bend them out of shape and then they will jump back into shape
  • Nanoparticles are really tiny
    • They are around 1-100 nanometres across (1nm – 0.000000001m)
    • Nanoparticles contain a few hundred atoms
    • Nanoparticles include fullerenes – molecules of carbon shaped like and hollow sound or closed tubes. The carbon atoms are arranged in hexagon rings – different fullerenes contain different numbers of carbon atoms
    • Fullerenes can be joined together to make very small but very strong tubes – e.g. they can be used to hold the graphite in tennis rackets together
  • Nanoparticles are becoming more and more widely used
    • They have a large surface area to volume ratio – so they could help make new industrial catalysts
    • You can use nanoparticles to detect a certain molecule
    • Nanotubes can be used to make stronger and lighter building materials
    • Sunscreen and deodorant have been made using nanoparticles so that they do their job but don’t leave white marks on your skin
    • Nano medicine is tiny fullerenes that can be more easily absorbed more easily by the body – so that they can deliver drugs straight into the body where it is needed
    • New lubricant coatings – developed using fullerenes – reduce friction
    • Nanotubes conduct electricity – tiny electric circuits for computer chips


  • Forces between molecules determine the properties of plastics
    • Strong covalent bonds hold atoms together in long chains – these bonds determine the properties of plastics
  • Weak Forces
    • Individual tangled chains of polymers held together by weaker intermolecular forces and are free to slide over each other
    • g. Thermo- softening polymer don’t have cross linking between chains – so the forces are easy to overcome and so easy to melt. When it cools the polymer hardens into shape
    • You can melt and remould these plastics
  • Strong Forces
    • These polymers have strong intermolecular forces between the polymer chains called crosslinks that hold it strongly together
    • g. Thermosetting polymers have crosslinks – these chains hold together in a solid structure, so the polymer doesn’t soften when heated – thermosetting polymers are strong, hard and rigid
  • How you make the polymer will affect its properties
    • The starting materials and reaction conditions will both affect the properties of a polymer
    • g. two types of polythene can be made using different conditions
      • Low density polythene which is flexible (used for bottles) – ethane is heated to a high temperature and put under high pressure
      • High density polythene (used for water tanks and drainpipes) – is made at a lower temperature and pressure