Unit 3: Chemistry in Society

• Metallic bonding


  The electrostatic force of attraction between positively charged ions and delocalised electrons
• Metallic elements


  • They are conductors of electricity because they contain delocalised electrons
• Reactions of metals


  1. Metal + oxygen → metal oxide

  2. Metal + water → metal hydroxide + hydrogen

  3. Metal + dilute acid → salt + hydrogen
• Metals can be arranged in order of reactivity


  • By comparing the rates at which they react
• Producing soluble salts from metals

  Excess metal is added to the appropriate acid, the mixture is filtered and the filtrate evaporated to dryness
• Reduction


  A gain of electrons by a reactant in any reaction
• Oxidation


  A loss of electrons by a reactant in any reaction
• In a redox reaction, reduction and oxidation take place at the same time
• Ion-electron equations


  1. Can be written for reduction and oxidation reactions

  2. Can be combined to produce redox equations
• Extraction of metals


  1. Metal ions are reduced forming metal atoms

  2. The method used depends on the position of the metal in the reactivity series

  3. Methods used: heat alone, heating with carbon or carbon monoxide, electrolysis
• Electrolysis


  The decomposition of an ionic compound into its elements using electricity
• A d.c. supply must be used if the products of electrolysis are to be identified
• Positive ions gain electrons at the negative electrode and negative ions lose electrons at the positive electrode
• Electrolytes


  Electrically conducting solutions containing ions
• Electrochemical cells


  • A simple cell can be made by placing two metals in an electrolyte
  • Another type of cell can be made using two half-cells (metals in solutions of their own ions)
  • An ion bridge (salt bridge) can be used to link the half-cells for ions to move across the bridge to complete an electrical circuit
  • Electricity can be produced in cells where at least one of the half-cells does not involve metal atoms (e.g. graphite rod)
• Factors affecting voltage in electrochemical cells

  • Different pairs of metals produce different voltages
  • The further apart elements are in the electrochemical series, the greater the voltage produced
• Electrons flow in the external circuit from the species higher in the electrochemical series to the one lower in the electrochemical series
• Ion-electron equations for electrochemical cells

  Can be written for the oxidation reaction, the reduction reaction, and the overall redox reaction
• The direction of electron flow can be deduced for electrochemical cells including those involving non-metal electrodes
• Polymers


  Long chain molecules formed by joining together a large number of small molecules called monomers
• Addition polymerisation


  A chemical reaction in which unsaturated monomers are joined, forming a polymer
• Repeating unit


  The shortest section of polymer chain which, if repeated, would yield the complete polymer chain (except for the end-groups)
• The structure of a polymer can be drawn given either the structure of the monomer or the repeating unit
• From the structure of a polymer, the monomer or repeating unit can be drawn
• Fertilisers


  Substances which restore elements, essential for healthy plant growth, to the soil
• Ammonia production


  1. Ammonia is produced by the Haber process: N2(g) + 3H2(g) ⇌ 2NH3(g)

  2. An iron catalyst is used to increase the reaction rate

  3. Ammonia is the starting material for the commercial production of nitric acid
• Nitric acid production


  The Ostwald process uses ammonia, oxygen and water to produce nitric acid, with a platinum catalyst
• Radioactive decay


  Changes in the nuclei of atoms, where unstable nuclei (radioisotopes) can become more stable nuclei by giving out alpha, beta or gamma radiation
• Alpha particles


  • Consist of two protons and two neutrons, carry a double positive charge, have a short range in air, and are stopped by paper
• Beta particles


  • Electrons ejected from the nucleus, able to travel further in air, but can be stopped by a thin sheet of aluminium, attracted to a positively charged plate
• Gamma rays


  • Electromagnetic waves emitted from within the nucleus, able to travel great distances in air, can be stopped by lead or concrete, not deflected by an electric field
• Balanced nuclear equations


  1. The sum of the atomic numbers on the left equals the sum on the right

  2. The sum of the mass numbers on the left equals the sum on the right
• Half-life


  The time for half of the nuclei of a particular radioisotope to decay
• The half-life of an isotope is a constant, unaffected by chemical or physical conditions
• Radioactive isotopes can be used to date materials
• Determining half-life


  From a graph showing a decay curve
• Calculations using half-life


  Relating number of half-lives, time, and proportion of radioisotope remaining
• Uses of radioactive isotopes


  • In medicine
  • In industry