4.9 - Reactions of the Halogens

• trend in oxidising ability

  falls down the group

  fluorine is such a powerful Oxidising aagent that you can't reasonably do solution reactions with it

  more reactive halogen Oxidises a less reactive one
• reaction with metals


  group 1: 2Li+X2→2LiX

  group 2: Mg+ X2→ MgX2

  form halide salts - metal is oxidised, halogen is reduced
• reaction of iodine with metals

  form iodides but due to polarisibility of the larger iodide ions the iodides form either small cations the like Li+ or highly charged cations like Al 3+ - essentially covalent
• reaction of fluorine with iron

  Oxidises iron to an iron (III) compound
• reaction of Chlorine with iron

  pass chlorine gas over hot iron & iron burns to form iron (Ill) Chloride
• reaction of bromine with iron

  less vigorous than with chlorine

  produces iron (IlI) bromide

  reddish-brown solid
• reaction of iodine with iron

  less vigorous

  produces grey iron (II) iodide - iodine Isn't a powerful Oxidising agent
• reaction of fluorine with aqueous Fe2+ ions

  whenever in solution fluorine reacts with water so doesn't react with Fe2+ ions
• reaction of chlorine and bromine with aqueous Fe2+ ions

  strong enough Oxidising agents to Oxidise iron (lI) ions to iron (Ill) ions
• reaction of iodine with aqueous Fe2+ ions

  not strong enough Oxidising agent so can't oxidise iron (II) compounds
• reaction of chlorine with non-metals

  reacts with most to form molecular Chlorides

  eg: PCl3 or PCl4 depending on supply of gas

  doesn't react directly with carbon, oxygen or nitrogen
• reaction of bromine with non-metals

  Oxidises non-metals to form molecular bromides

  eg: bromine vapour & hydrogen react smoothly with a pale bluish flame
• reaction of iodine with hydrogen

  H2 + I2 → 2HI

  it's a reversible reaction