covalent bonding

• A covalent bond is the electrostatic attraction between two nuclei and a shared pair of electrons.
• covalent bonding forms molecules
• simple molecular structure and boiling point

  contains many individual covalently bonded molecules held together by weak intermolecular forces of attraction

  low boiling point as the weak intermolecular forces need to be broken

  as the mass of the structure increases (mr increases) the intermolecular forces get stronger and boiling point gets higher
• giant covalent structureand boiling point

  many atoms all covalently bonded together

  eg. diamond, graphite, silicon dioxide

  very high boiling points as you need to separate the strong covalent bonds

  no ions or delocalized electrons so poor conductors

  apart from graphite
• graphite


  layers of giant covalent structures (hexagonal lattice structures of carbon) (called graphenes) with weak forces of attraction holding them together so they can slide over eachother - making it soft and why it is used as a lubricant

  layers have delocalised electrons between them which are free to move so can conduct electricity

  high melting point because of strong covalent bonds
• do covalent structures conduct electricity

  
  

  covalent structures generally don't conduct electricity as they lack ions or delocalized electrons
• how are covalent bonds formed

  Covalent bonds are formed when two non-metal atoms share pairs of electrons to achieve a full outer shell.
• diamond

  tetrahedral lattice of carbon atoms

  giant covalent structure

  high melting point as many (because of tetrahedral shape) strong (covalent) bonds need to be broken.

  hard as lots of energy required to scratch and break strong covalent bonds
• c60 (buckminster) fullerene

  Its molecules are made up of 60 carbon atoms joined together by strong covalent bonds in a hollow sphere.

  There are weak intermolecular forces between molecules of buckminsterfullerene, so is slippery and has a low melting point.

  can't conduct electricity as delocalized electrons can't move across molecules
• allotrope

  different form of same element