the halogens

• Displacement reaction

  A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions
• Down the group of halides, reducing power increases.


  This trend is explained by the increasing number of electron shells.

  This causes the distance between the outer electrons and the nucleus to increase, so that attraction decreases.

  Therefore, the electron is more easily lost and donated to another atom which reduces that atom.
• Down the group, the ability of the halogens to act as an oxidising agent decreases


  This makes F2, Cl2 and Br2​ stronger oxidising agents than I2.

  Therefore, F2, Cl2, Br2​ will oxidise I− to I2.
• acid-base reaction when sodium bromide reacts with concentrated sulfuric acid

  NaBr (s) + H2SO4 (l) → NaHSO4 (s) + HBr (g)
• • At room temperature:
  • Fluorine→a pale yellow gas
  • Chlorine→pale green gas
  • Bromine→a red-brown or red or brown liquid
  • Iodine→is a solid with a black colour
  • Astatine→is a solid
• • As you go down group 7
  • full shells → increases
  • shielding → increases
  • atomic radius → increases
  • distance between shared electron pair and nucleus → increases
• • Explain trend in boiling point
  • Boiling point increases down the Group 7 halogens (fluorine to iodine) due to increased London dispersion forces
• Halogens act as → oxidising agent
• Bromine displaces → Iodide
• Chlorine displaces → Bromide and Iodide
• Fluorine displaces → Chloride, Bromide and Iodide
• Which halogens oxidise iodide ions to iodine? F, Cl, Br
• What is added to test halide ions in an aqueous solution → Silver nitrate (AgNO3) solution
• • Identifying Halides using Silver Nitrate
  • silver fluoride → no precipitate
  • silver chloride → white colour precipitate
  • silver bromide → cream coloured precipitate
  • silver iodide → yellow coloured precipitate
• • Why does AgF form no precipitate → AgF is soluble in water
• What can cause impurities in the halide solution → any carbonate and hydroxide ions as will form precipitates with silver nitrate, giving a false positive result
• How can we get rid of impurities in the halide solution → acidfy it with dilute nitric acid
• • Using Ammonia to Identify Silver Halides
  • soluble in dilute ammonia → F- and Cl-
  • soluble in concentrated ammonia → F-, Cl- and Br-
  • which is insoluble in any concentration → I-
• Examples of disproportionation reactions:

  • Chlorine + water
  • Chlorine + cold, dilute sodium hydroxide
• NaClO is used as household bleach
• Chlorine is used in water purification
• Cl2 (aq) + H2O (l) -> HClO (aq) + HCl (aq)
• HClO is called chloric (I) acid
• Chloric acid can act as a weak bleach
• Cl2 (aq) + 2NaOH (aq) -> NaClO (aq) + NaCl (aq) + H2O (l)
• Chlorine gas is toxic
• As you go down group 7

  • electronegativity → decreases
  • boiling point → increases
  • oxidising ability → decreases
  • reducing ability → increases