Halogens

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  • Created by: KatieL
  • Created on: 29-12-12 18:33
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  • Halogens
    • Group 7
      • Flourine; Chlorine; Bromine; Iodine; Astatine
        • Flourine- highly reactive   not counted in all the trends
        • Astatine- radioactive
      • All have 7 electrons in their outer shell
      • Found as  X2  simple covalent molucles
    • Trends
      • Reactivity
        • Decreases as you down the group
          • Distance from the nucleus increases, harder to gain an extra electron
      • Atomic Radius
        • Increases as you go down the group
          • More electrons, so more energy levels
      • Melting/ Boiling Point
        • Increases as you go down the group
          • More electrons so the dipole is larger and the Van der Walls forces are larger
      • Reducing power
        • Displace  other halide ions
          • Decreaes down the group
            • Reactivity  decreases
    • Testing for Halides
      • Cyclohexance
        • Cyclohexane layer changes colour
          • Chlorine- yellow/green
          • Bromine- Orange/Brown
          • Iodine- Purple
      • Silver Nitrate
        • Forms a precipitate
          • Chlorine- White ppt. dissolves in dilute ammonia
          • Bromine-  Cream ppt. Dissolves in conc. ammonia
          • Iodine- Yellow ppt. Insoluble
        • Ag+  + X-  -->  AgX
    • Disproportionation
      • Both oxidised and reduced in the same reaction
        • Reaction with  Sodium Hydroxide
          • Cold
            • X2 + 2 NaOH --> NaXO + NaX + H2O
          • Hot
            • 3X2 + 6NaOH --> NaX03 + 5NaX + 3H2O
    • Uses
      • Chlorine is  used to clean water as it kills most bacteria
        • Flouride is put in toothpaste
          • Hydrogen Floride is used to etch glass

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