chemistry

• giant ionic lattice

  has billions of electrostatic forces working in all directions once they form oppositely charged ions the ions can be attracted to each other
• describe bonding of sodium chloride

  • it is a giant ionic lattice made of positive sodium ions and negative chlorine ions
  • ions are oppositely charged
  • held together by electrostatic force of attraction
  • force acts in all direction
• properties of ionic substances:

  • high melting points - break lots of strong ionic bonds, needs lots of energy
  • conducting electricity when liquid - charged electrons free to move
• covalent structures


  eg.

  diamond, graphite, silicon dioxide or simple substances (eg. hyrogen, water, carbon dioxide)
• covalent structures never conduct electricity as they have no free electrons or charged particles in these structures
• graphite propertise:


  • layers of carbon - covalently bonded to 3 others
  • electrons are free to travel through the graphite they are delocalised - conducts electricty
  • layers themselves are strong but free to slide over each other - soft and slippery
• simple molecular substances


  have weak intermolecular force - low melting points, cannot conduct electricity

  • there are strong covalent bonds within the molecule (intramolecular) but weak forces between molecules (intermolecular) so easy to pull away
• graphene


  one layer of graphite

  uses - electronics, very effective conductor of electricity due to free electrons, very strong so useful in advanced materials (composites)
• fullerene


  a hollow cage of carbon atoms

  uses - drugs delivery for medical applications, lubricants (weak forces between cages so easy for cages to slip over each other), catalysts
• nanotube


  a hollow tube of carbon atoms

  uses - high tensile strength so can be used in composite materials eg. tennis rackets, high electrical conductivity
• chemical bonding involves either transferring or sharing electrons in the highest occupied energy levels (outer shells) of atoms in order to achieve the electron arrangement of a noble gas
• when atoms form chemical bonds, they form ions
• compounds formed from metals and non-metals consists of ions
• examples of covalently bonded substances:

  H2, Cl2, O2, N2, HCl, H20, NH3, CH4

  and diamond and silicon dioxide
• substances that consist of simple molecules have only weak forces between molecules (intermolecular forces). it is there intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils
• intermolecular forces are weak compared with covalent bonds
• in graphite one electron from each carbon atoms is delocalised, these electrons allows graphite to conduct heat and electricity
• fullerenes can be used for drug delivery into the body, in lubricants, as catalysts and in nanotubes for reinforcing materials
• nanoparticles

  show properties different from those for the same materials in bulk and have a high surface area to volume ratio. which may lead to the development of new computers, new catalysts, new coatings, highly selective sensors, stronger and lighter construction materials, and new cosmetic such as suntan creams and deodorants.
• copper good for electrical wiring and plumbing:

  • good conductor of heat and electricity
  • can be bent but is hard enough to be used to make pipes or tanks
  • does not react with water
• metals that are more reactive than carbon. eg. aluminium, are extracted by electrolysis of molten compounds. the use of large amounts of energy in the extraction of these metals makes them expensive
• copper can be extracted by phytomining or bioleaching
• phytomining uses plants to absorb metal compounds that the plants are burned to produce ash that contains the metal compounds
• bioleaching uses bacteria to produce leachate solutions that contain metal compounds
• copper can be obtained from solutions of copper salts by electrolysis
• copper can be obtained from solutions of copper salts by displacement using scrap iron
• we should recycle metals because extracting them uses limited resources, and it is expensive in terms of energy and in terms of effects on the environment