C2.3

• Carbon


  Can form four covalent bonds
• Organic compounds


  • Occur due to carbon's ability to form families of similar compounds, chains and rings
• Diamond


  Each carbon is joined to 4 other carbons covalently. It's very hard, has a very high melting point and does not conduct electricity.
• Graphite


  Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings with no covalent bonds between the layers. The layers can slide over each other due to weak intermolecular forces, making graphite soft and slippery. One electron from each carbon atom is delocalised, allowing graphite to conduct electricity.
• Fullerenes


  • Molecules of carbon atoms with hollow shapes, based on hexagonal rings of carbon atoms that may also contain rings with five or seven carbon atoms. The first fullerene discovered was Buckminsterfullerene (C60), which has a spherical shape.
• Carbon nanotubes


  • Cylindrical fullerenes with very high length to diameter ratios. Their properties make them useful for nanotechnology, electronics and materials.

  
• Graphene


  A single layer of graphite. Has properties that make it useful in electronics and composites.
• Energy transferred TO a compound

  Melting, boiling
• Energy transferred FROM a compound

  Condensing, freezing
• Covalent bonds


  Very strong
• Ionic bonds


  Very strong - electrostatic forces of attraction
• Intermolecular forces


  Simple molecules are melted/boiled easily as the weak intermolecular forces are overcome and not the covalent bonds. Ionic compounds have higher melting and boiling points as the electrostatic forces of attraction are harder to overcome. Macromolecular substances do not have intermolecular forces and are very hard to break down as the covalent bonds must be overcome.
• Different temperatures at which substances change state are due to the factors of energy transfer, relative strength of chemical bonds, and intermolecular forces.
• Temperature below melting point: solid
• Temperature between melting and boiling point: liquid
• Temperature above boiling point: gas
• Ionic compounds, simple molecules, giant covalent structures, polymers, metals


  • Their bulk properties are related to the different types of bonds they contain, their bond strengths in relation to intermolecular forces, and the ways in which their bonds are arranged.
• Nanoparticles


  1. 100 nanometers across, containing a few hundred atoms. Smaller than fine particles (PM2.5) which have diameters between 100 and 2500 nm, and coarse particles (PM10) which have diameters between 1 x 10^-5 m and 2.5 x 10^-6 m.

  
• As the side of a cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10.
• Nanoparticles


  • Have a very large surface area to volume ratio. Atoms on the surface of a material are often more reactive than those in the centre, so a larger surface area means the material is more reactive.
• Uses of nanoparticulate materials

  • Good catalysts due to high surface area to volume ratio
  • Produce highly selective sensors
  • Stronger, lighter building materials (nanotubes)
  • New cosmetics that make no white marks
  • Lubricant coatings that reduce friction (for artificial joints and gears)
  • Electrical circuits (nanotubes conduct electricity)
• Possible risks associated with nanoparticulate materials