Chemistry: Structure and Properties 1

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  • Created by: Catherine
  • Created on: 20-04-13 14:31
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  • Chemsitry: Structure and Properties
    • Giant Ionic Structures
      • ionic compounds have giant structures
        • strong electrostatic forces hold ions together
      • they are solids at room temperature
        • lots of energy is needed to overcome ionic bonds and melt the solid
          • therefore ionic compounds have high melting and boiling points
      • when an ionic compound has been melted, ions are free to move
        • this allows them to carry electrical charge
          • so molten ionic compound conducts electricity
      • some ionic solids dissolve in water
        • this is because water molecules can split up the lattice
          • ions are free to move in solution
            • so ionic compound solution conducts electricity
    • simple molecules
      • atoms within a molecule are held together by strong covalent bonds
        • bonds only act within the molecule
          • so simple molecules have very little attraction for one another
      • substances made from simple molecules have low melting and boiling points
        • this is because little energy is needed to break the weak intermolecular  bonds
      • they do not conduct electrical charge
        • simple molecules have no overall charge so cannot carry charge
      • simple molecular substances with the smallest molecules have the weakest intermolecular  forces
        • these are gases at room temperature
      • larger molecules have stronger attractions
        • these may be liquids at room temperature or solids with low melting points
    • giant covalent structures
      • it takes an enormous amount of energy to break these lattices
        • so these substances have high melting points
      • diamond
        • regular 3D giant structure
        • every carbon atom bonds to   4 other carbon atoms
          • this makes diamond hard and transparent
      • graphite
        • each carbon atm bonds with 3 other carbon atoms
        • giant, flat 2D layers
          • no covalent bonds between layers
            • so they slide over each other, making graphite slippery and grey
      • graphite and fullerenes
        • in carbon, the layers are flat sheets of hexagons
          • one electron from each carbon atom is delocalised
            • this allows graphite to conduct heat and electricity
        • fullerenes are large molecules formed from hexagonal rings of carbon atoms
          • the rings join together to form cage-like shapes with different numbers of C aoms
        • scientists are finding many uses for fullerenes
          • e.g. drug delivery, lubricants, catalysts, reinforcing materials

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