8.2 Halogens

• Halogens exist as diatomic molecules in the gaseous state
• In the solid state halogens form simple molecular lattices with weak London forces
• Down the group the molecules contain more electrons and have stronger London forces
• Boiling point increases down the group
• In redox reactions halogens act as strong oxidising agents
• Reactivity decreases down the group

  • shielding increases
  • atomic radius increases
  • attraction between nucleus and outer shell decreases
• Redox reactions between halogens and aqueous halides can be used to show the reactivity of halogens decrease down the group
• Chlorine reacts with bromide and iodide ions
• Bromine reacts with iodide ions
• Disproportionation is when an element is both oxidised and reduced in the same reaction
• Chlorine reacts with water in a redox reaction to form two acids = chloric acid (HClO) and hydrochloric acid

  • this reaction is used in water treatment to kill bacteria
• Chlorine reacts with cold, dilute sodium hydroxide to form sodium chloride, sodium chlorate (NaClO) and water
• Sodium chlorate is used in household bleach
• At room temperature

  • Fluorine is a yellow gas
  • Chlorine is a pale green gas
  • Bromine is a red-brown liquid
  • Iodine is a dark grey solid
• Oxidising agent = substance that removes electrons from other species and gains electrons itself
• Colour of chlorine in water = pale green
• Colour of chlorine in cyclohexane = pale green
• Colour of bromine in water = orange
• Colour of bromine in cyclohexane = orange
• Colour of iodine in water = brown
• Colour of iodine in cyclohexane = violet