properties of materials

• Why does graphite conduct electricity?

  Graphite only has 3 carbon bonds, meaning there is a free bond. This means that there are delocalised electrons, which carry a charge and can therefore conduct electricity.
• allotropes - two substances made from the same element, that are in the same physical state but have different structures
• diamond


  has high melting and boiling points due to the strong covalent bonds. each carbon atom is bonded to 4 other carbon atoms, therefore it cannot conduct electricity because it has no delocalised electrons.
• graphite


  is weaker than diamond because of the weak intermolecular forces, which allow the layers of graphene to slide over each other.
• fullerenes


  are allotropes of carbon, made by bending sheets of graphene into hollow structures (spheres). nanotubes made from fullerenes are useful in electronics
• fullerenes


  they are useful because they have a high surface area to volume ration
• alloy - a metal combined with one or more elements
• nanoparticles


  have a diameter of 1 to 100 nanometres.
• nanoparticles


  have a very large surface area to volume ratio.

  use them as catalysts.
• nanoparticles


  silver nanoparticles have antibacterial properties
• nanoparticles - risks


  still relatively new, their effects on our bodies isn't clear yet.
• nanoparticles - sunscreens

  more effective against harmful UV rays, they provide better skin coverage. but it is not clear if they can be absorbed by the skin and damage our cells.
• polymers are formed when lots of small molecules called monomers are joined together
• plastic is an example of a polymer
• strong covalent bonds hold the atoms together in polymer chains. but the forces [intermolecular] between the chains determine the properties.
• polymers: weak forces


  if the plastic is made up of chains that are only held together by weak intermolecular forces, then the chains will be free to slide over each other. this means that the plastic wcan be stretched easily, and will have a low melting point [because weak intermolecular forces require less energy to be broken down.]
• polymers: strong forces


  some plastic have stronger bond between polymer chains [e.g. covalent bonds or cross-links]. these plastics have higher melting points, are rigid and can't be strectehd as the cross-links hold the chains firmly together.