G7

• Fluorine is pale yellow gas
• Chlorine is pale green gas
• Bromine is brown- orange liquid
• Iodine is a grey solid
• Boiling point for group 7 increases because atoms get bigger which means larger van der waals forces due to increase in size
• Electronegativity for group 7 decreases down the group. This is because as the atom gets bigger there is more shielding and more distance between the positive nucleus and the bonding electrons
• Reactivity in halogens decrease down the group
• Halogens are less oxidising as you go down the group
• Halogen will displace a halide if halide is lower in the periodic table
• Cl2 + 2Br- -> 2Cl- +Br2

  Br is displaced, solution will be colourless to orange
• Cl2 + 2I- -> 2CL- + I2

  I2 is displaced, solution turns from colourless to brown
• Br2 + 2I- -> 2Br- + I2

  I2 is displaced solution goes from colourless to brown
• Bleach made by using a disproportionation reaction
• chlorine + sodium hydroxide = sodium chlorate I (bleach)
• 2NaOH + Cl2 --> NaClO + NaCl + H20
• Uses of sodium chlorate (NaClO)

  • cleaning agents
  • treating water
  • Bleaching paper and fabrics
• adding water to chlorine will make chlorate ions which are useful in killing bacteria

  used for drinking water and pools
• H20 + Cl2 --> 2H+ +Cl- + ClO-
• Sunlight can decompose chlorinated water too

  No ClO- is made

  2H20 + Cl2 --> 4H+ +2Cl- + O2
• Advantages of chlorinating water:

  • Destroy microorganisms
  • reduces bacteria build up
  • Reduces growth of algae that can discolour water and give it a bad taste
• Disadvantages of chlorinating drinking water:

  • Chlorine gas is toxic
  • Liquid chlorine causes severe chemical burns
  • Chlorine can react with organic compounds that could potentially cause cancer
  • But chlorinating water would result in a cholera epidemic
• Halide ions lose electrons so they are reducing agents
• As we go down the group the ionic radius increases

  Distance between nucleus and outer electron increase also an increase in shielding

  This means the attractive force is weaker

  Outer electron is lost more readily so this means I- is a stronger reducing agent compared to F-
• Test with

  • sulfuric acid
  • silver nitrate solution

  to prove the strength of reducing agents increases down the group
• some halide ions can reduce CONCENTRATED sulfuric acid
• NOT REDOX REACTIONS :

  • NaCl + H2SO4 --> NaHSO4 + HCL (white misty fumes)
  • NaBr + H2SO4 --> NaHSO4 + HBr (can be reduced further)
  • NaI + H2SO4 --> NaHSO4 + HI (can be reduced further)
• 2Br --> Br2 + 2e-

  H2SO4 + 2H+ --> SO2 + 2H20

  overall ionic equation : H2SO4 + 2H+ + 2Br --> Br2+ SO2 + 2H2O

  
  

  orange fumes produced
• Iodide can reduce sulfur further than bromide
• further reduction of sulfure with iodide :

  6I- --> 3I2 + 6e-

  H2SO4 + 6H+ + 6e- --> S + 4H2O

  Overall ionic equation : H2SO4 + 6I - +6H+ --> 3I2 + S+ 4H20

  
  

  yellow solid of sulfur produced
• Reducing S further to make H2S

  8I- --> 4I2 + 8e-

  H2SO4 + 8H+ + 8e- --> H2S + 4H2O

  Overall ionic equation: H2SO4 + 8I- + 8H+ --> 4I2+ H2S + 4H2O

  
  

  rotten egg smell of H2S
• Test for halides using silver nitrate and confirm with ammonia solution
• To test halides with silver nitrate add nitric acid first then silver nitrate

  
  

  Chloride forms white precipitate

  Bromide forms cream precipitate

  Iodide forms yellow precipitate

  
  

  Nitric acid reacts with any other carbonate or anions
• You can further test halide and silver nitrate by adding ammonia

  Chlorine - the white precipitate will dissolve in dilute NH3

  Bromine - the cream precipitate will dissolve in concentrated NH3

  Iodine - the yellow precipitate will be insoluble in concentrated NH3