halogens

• Fluorine (F2)


  Very pale yellow gas, highly reactive
• Chlorine (Cl2)


  Greenish, reactive gas, poisonous in high concentrations
• Bromine (Br2)


  Red liquid, gives off dense brown/orange poisonous fumes
• Iodine (I2)


  Shiny grey solid, sublimes to purple gas
• All halogens exist as diatomic molecules
• Electronic configuration of group 7 elements

  Outer shell s2p5
• Group 7 elements will often react by gaining of one electron in redox reactions to form 1– ions
• Displacement reactions of halide ions by halogens

  1. A halogen that is more reactive will displace a halogen that has a lower reactivity from one of its compounds

  2. Chlorine will displace both bromide and iodide ions; bromine will displace iodide ions
• The reactivity of the halogens decreases down the group as the atoms get bigger with more shielding so they less easily attract and accept electrons. They therefore form -1 ions less easily down the group
• Observations if an organic solvent is added

  • Chlorine = colourless, Bromine = yellow, Iodine = purple
• Disproportionation reactions of chlorine

  Cl2(g) + H2O(l) → HClO(aq) + HCl(aq)

  Cl2(aq) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H2O(l)
• Chlorine is used in water treatment to kill bacteria
• Reactions of halide ions with silver nitrate

  Fluorides produce no precipitate

  Chlorides produce a white precipitate

  Bromides produce a cream precipitate

  Iodides produce a pale yellow precipitate
• If the hot sodium hydroxide is used a different disproportionation reaction occurs forming sodium chlorate(V)