Covalent Bonding

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  • Covalent Bonding
    • Molecules
      • form when 2 or more atoms bond together
      • held together by strong covalent bonds
        • can be single, double or triple bonds
          • single bonds
            • 2 atoms share electrons so they have both got full outer shell
            • 1 shared pair of electrons
              • both positive nuclei are attracted electrostatically to shared electrons
            • e.g. I2, HCl, H2, CH4
          • double & triple bonds
            • shown using multiple lines
            • 1 carbon atom bonds to 2 oxygen atoms. Each carbon atom has to form 4 bonds. 2 double bonds are formed
      • simple covalent compounds
        • made up of lots of individual molecules
          • atoms in molecules held together by intermolecular forces
            • determine properties
              • in general, low melting & boiling points & electrical insulators
    • Giant Covalent Structures
      • type of crystal structure
      • huge network of covalently bonded atoms
      • aka macromolecular
      • graphite
        • carbon atoms arranged in sheets of flat hexagons covalently bonded with 3 bonds each
          • 4th outer electron of each carbon  is delocalised
          • sheets are bonded together by weak van der Waals forces
        • properties
          • slippery & used in dry lubricants
            • weak bonds between layers are easily broken so sheets can slide over eachother
          • electrical conductor
            • delocalised electrons free to move so electrical current can flow
          • high melting point - over 3900k
            • strong covalent bonds
          • insoluble in a solvent
            • covalent bonds in sheets too difficult to break
        • low density - used to make strong lightweight sports equipment
          • layers are quite far apart compared to length of covalent bonds
      • diamond
        • each carbon atom bonded to 4 other carbon atoms
        • tetrahedral shape
        • properties
          • high melting point
            • over 3800k due to lots of covalent bonds needing to be broken
          • extremely hard
            • used in diamond tipped saws & drills
          • good thermal conductor
            • vibrations travel through the stiff lattice easily
          • can't conduct electricity
            • all outer electrons are held in localised bonds
          • like graphite, won't dissolve in any solvent
    • Co-ordinate (dative covalent) bonds
      • one of the atoms provide both of the shared electrons
      • e.g. ammonium ion
        • nitrogen atom in an ammonia molecule donates a pair of electrons to a hydrogen ion
      • forms when 1 of the atoms in the bond has a lone pair of electrons & the other doesn't have any electrons available to share

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