group 17 halogens

• Physical properties of halogens

  • Exist as diatomic molecules
  • Low melting and boiling points
  • Coloured (element itself)
  • Poor conductors of electricity
• Chemical properties of halogens

  • Reaction of metals with halogens
  • Forms ionic metal halides (solids)
  • Reacts with most metals to form halide salts
  • Displacement reaction
• More reactive halogen


  Greater tendency to gain electrons to become halide
• Fluorine does not undergo displacement reaction
• Fluorine reacts violently with water -> hydrogen fluoride gas + mixture of oxygen and ozone
• Reaction of halide ions with silver nitrate solution (test for halides)


  When silver nitrate solution is added to a halide solution, ppt of silver halide is formed
• Down the group


  Melting and boiling point increases

  • explanation: molecular mass and size of each molecule increases ⇒ strength of intermolecular forces of attraction increases ⇒ more energy needed to overcome IMF between molecules
  • a larger electron cloud (larger molecules) translates to stronger IMF due to a higher electron cloud density
• Down the group


  Color intensities increase
• Halogen colours


  • Chlorine: yellow green vapour
  • Bromine (Br2): red brown liquid (rtp;l), red brown/brown aqueous solution (aq), red brown/brown vapour (g)
  • Iodine: purple black solid (rtp) (s), brown aqueous solution (aq), violet in organic solvent, violet vapour (g)
• All halogen vapour is poisonous
• Iodine cannot be in liquid state (sublimes; solid ⇒ gas)
• Down the group


  Density increases
• Down the group


  Reactivity decreases

  • number of filled principal quantum shells increases
  • distance between nucleus and valence electrons increases
  • EFOA between nucleus and valence electrons decreases
  • harder for the atom to attract another electron and more difficult to form the X- ion
• displacement reaction explanation

  • explanation:
  • as A is more reactive than B and gains electrons more readily than B, A displaces B from aqueous CB
  • colourless aqueous CA and red brown aqueous B are formed