Halogens

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  • Halogens
    • Trend in melting/boiling points
      • Gas, gas, liquid, solid
      • Increases as you go down the group
        • As you go down the group the atomic radius increases
          • Each extra shell contains more electrons
            • Larger van der waals forces
              • Needs more energy to break
                • Increases as you go down the group
                  • As you go down the group the atomic radius increases
                    • Each extra shell contains more electrons
                      • Larger van der waals forces
                        • Needs more energy to break
      • Trend in electronegativity
        • The relative tendency of an atom to attract electrons in a covalent bond
        • Decreases down the group
          • Atomic radius increases
            • Nucleus is less able to attract a bonding pair of electrons
      • Displacement reactions
        • Between halide ions and halogens
        • Oxidising strength decreases down the group
          • Electron accepters that are themselves reduced
          • A halogen that has strong oxidising strength will displace a halogen with less oxidisation strength
            • Chlorine will displace both bromide and iodide ions
              • Very pale green solution turns yellow in the presence of Bromide ions
              • Very pale green solution turns brown in the presence of iodide ions
            • Bromine will displace iodide ions
              • Yellow solution turns brown with iodide ions present
            • Iodine won't displace anything
              • Solution stays brown
      • Reactions of halide ions with silver nitrate
        • Used to identify which halide ion is present
        • 1) Add Nitric acid
          • Reacts any carbonates to prevent formation of AgCO3
            • This would mask the desires observations
        • 2) Add silver nitrate in drops
          • Fluoride won't form a precipitate
          • Chloride will form a white precipitate
          • Bromide will form a cream precipitate
          • Iodide will form a pale yellow precipitate
        • 3) Add ammonia solution
          • This is done because it is hard to tell the difference between white cream and pale yellow
          • Dilute ammonia dissolves silver chloride precipitate
          • Concentrated ammonia dissolves silver bromide precipitate
          • Silver iodide won't dissolve
      • Reaction of halide salts with concentrated sulphuric acid
        • Reducing power increases down the group
          • A reducing agent donates electrons
          • Because atomic radius increases down the group
            • Outer electrons are easier to give away as the nucleus has less of a pull on them
        • Fluride and Chloride aren't strong enough reducing agent's to reduce S in H2SO4
          • Mean's only acid base reactions occur
            • No redox reactions
            • Gives off white steamy fumes
        • Bromide has an inital acid based reaction and then a redox
          • Reduces the sulphur in H2SO4 from +6 to +4 in SO2
        • Iodide is the strongest reducing agent
          • Reduces sulphur from +6 to +4 in SO2
            • Then reduces it to O in S and -2 in H2S
          • Bad egg smell
      • Disproportionation reactions of chlorine and chlorate(l)
        • A reaction where an element simultaneously oxidises and reduces
        • Chlorine with water
          • Chlorine is both reducing and oxidising
            • Add a universal indicator and it will first turn red due to acidity
              • It will then turn colourless as HClO bleaches the colour
        • Chlorine with water in sunlight has a different reaction
          • Will react the same up until equilibrium
            • Greenish colour of chlorine fades as Cl2 reacts to form O2
        • Chlorine is used to treat drinking water and swimming pools
          • It kills bacteria
          • It's health benefits outweigh it's toxic effects
      • Reactions of chlorine with cold/dilute sodium hydroxide
        • Chlorine and bromine/iodine will react with cold sodium hydroxide
          • NaOH
        • The colour of the halogen will fade to colourless
        • Mixture of NaCl and NaClO are used in bleach
          • Also kills bacteria and disinfects

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