Group 7

• Trends in group 7:

  melting points increase as van der waals increases

  ionisation energy decreases

  oxidising power decreases

  electronegativity decreases
• Uses of chlorine:

  Forms chlorate ions which are used in water purifcation and bleach production
• Identifying Halides:

  1. dissolve halide in water
  2. add nitric acid to remove impurities like Carbonates
  3. Add silver , if no precipitate forms, the halide is fluorine
  4. If a precipitate forms: white = chlorine, cream = bromine, yellow = iodine
  5. Add dilute ammonia, if the precipitate dissolves then the halide is chloride
  6. Otherwise add concentrated ammonia: if the precipitate dissolved then the halide is bromide and otherwise is Iodide
• Down group 7, electronegativity decreases
• Down group 7, Boiling points increase as there are more electrons and a greater surface area leading to stronger van der waals
• Water purification:

  Cl2 + H2O <-> HCL + HClO, where the ClO- ions are responsible for killing pathogens

  The reaction does not occur when UV is present and instead:

  2Cl2 + 2H2O -> 4HCl + O2
• Bleach production reaction:

  Cl2 (aq) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)
• why is chlorine added water?

  Chlorine kills pathogens in water and prevents deaths from water-borne disease and is not that harmful in low concentrations
• Appearance at room temperature:

  F2 - pale yellow gas

  Cl2 - Green gas

  Br2 - Red-brown liquid

  I2 - grey solid