Group 7

• Florine (F2)


  Yellow gas
• Chlorine (Cl2)

  Green gas
• Bromine (Br2)


  Orange liquid
• Iodine (I2)


  Black solid

  Purple gas

  Orange solution
• Testing for halides

  • halide solution + nitric acid to react with anion impurities (e.g. hydroxide, carbonate)
  • + silver nitrate to form the precipitate (silver halide)

  AgCl- white

  AgBr- cream

  AgI- yellow

  
  

  Add dilute NH3- AgCl redissolves

  Add concentrated NH3- AgBr redissolves
• The best oxidising agent is F2 as it most easily gains electrons
• The best reducing agent is I- as it most easily loses electrons
• NaCl + H2SO4 -> HCl(g) + NaHSO4


  HCl(g) gives white/steamy fumes

  Acid/base reaction, not redox as Cl- is a weak reducing agent

  same reaction and observations with F-
• NaBr + H2SO4 -> HBr(g) + NaHSO4

  2HBr(aq) + H2SO4 -> SO2(g) + H2O + Br2(g)


  HBr(g) gives white/steamy fumes

  Br- is a better reducing agent than Cl- or F- so there's an extra step

  SO2(g) is a choking gas

  Br2(g) gives off brown fumes
• NaI + H2SO4 -> HI(g) + NaHSO4

  8HI + H2SO4 -> H2S(g) + 4H2O + 4I2(s)


  HI(g) gives off white/steamy fumes

  I- is a very good reducing agent so extra step

  H2S(g) has a foul/eggy smell

  I2 is a black solid/purple gas
• Electronegativity decreases as you go down Group 7.

  • This is because atomic radius increases and so electrons experience less attraction to the nucleus.
  • Electrons become further away from the nucleus and so experience a lower attraction.
  • This means that the electronegativity is lower.
• Boiling points increase down the group. At room temperature:

  • Fluorine and chlorine are gases.
  • Bromine is a liquid.
  • Iodine is a solid.
  • This is because elements have more electrons as you go down Group 7.
  • This causes an increase in van der Waals forces.
  • Stronger van der Waals forces means greater intermolecular forces.
  • This means a higher boiling point.
• Boiling points increase down the group. At room temperature:

  • Fluorine and chlorine are gases.
  • Bromine is a liquid.
  • Iodine is a solid.
  • This is because elements have more electrons as you go down Group 7.
  • This causes an increase in van der Waals forces.
  • Stronger van der Waals forces means greater intermolecular forces.
  • This means a higher boiling point.
• All silver halides precipitate out of aqueous solution.

  • When ammonia is added, they may dissolve again.
  • Solubility in ammonia decreases as you go down Group 7.
• Halides react differently with sulfuric acid depending on their reducing ability:

  • Reaction with a fluoride or chloride produces HCl or HF.
  • Reaction with a bromide produces some Br2 and some SO2.
  • Reaction with an iodide produces I2 immediately and will reduce the sulfur to H2S - a toxic molecule that smells like eggs.