displacement

• fluorine (F2)

  colour = pale yellow

  state = gas
• Chlorine (Cl2)

  colour = green

  state = gas
• Bromine (Br2)

  colour = red-brown

  state = liquid
• Iodine (I2)

  colour = grey (sublimes to purple gas)

  state = solid
• The boiling points of halogens increase down the group

  • because the size of molecule increases so the strength of van der waals forces also increases
  • therefore more energy has to be put into breaking the forces increasing the melting and boiling points
• Electronegativity (ability to attract electrons) decreases down the group

  • the atomic radii increases as the atom gets larger so the outer electrons are further away from the nucleus decreasing effects of nuclear attraction
  • and more shielding so there is less attraction between the positive nucleus and the outer electrons
• when halogens react they gain 1 electron to become halide ions, this means they are oxidising agents

  • in this process they are reduced (gain an electron)
  • while oxidising other ions (ability to take electron from ion/ loose electrons)
• oxidising ability of halogens decrease down a group

  • atoms become larger and the outer electrons become further from the nucleus decreasing effects of nuclear attraction
  • so the ability to take electrons from halide ions decreases down a group
• a halogen will displace a halide from a solution if the halide is below it in the periodic table = the halogen will be more electronegative with a higher oxidising ability

  • chlorine > bromine > iodine

  (chlorine will displace bromide and iodide ions, bromine will displace iodide ions)
• Displacement reactions:

  A) green

  B) yellow

  C) Br

  D) brown

  E) no

  F) yellow

  G) brown

  H) brown

  I) no

  
• The colour of the solution in the test tube shows which free halogen is present in solution.

  • Chlorine =very pale green solution (often colourless)
  • Bromine = yellow solution
  • Iodine = brown solution (sometimes black solid present)
• Displacement reaction:

  Chlorine + Potassium bromide ----> Potassium chloride + Bromine

  Cl2 (aq) + 2KBr (aq) ----> 2KCl (aq) + Br2 (aq)

  = aqueous bromine is yellow

  • ionic equation

  Cl2 (aq) + 2Br– (aq) ----> 2Cl- (aq) + Br2 (aq)