Halogens

• The Halogens


  • The most reactive nonmetals in the periodic table
  • Chlorine (gas) is green, bromine (liquid) is orange, and iodine (solid) is purple
  • Halogens form diatomic molecules joined by a single covalent bond (seven outer electrons in each shell)
  • They have a simple covalent structure, resulting in weak van der waals forces between the molecules, meaning very low boiling points
  • Halogens get bigger in size and darker in colour down the group
  • The state of the halogen (whether it is liquid, solid or gas) is a result of the strength of the London dispersion forces
  • The more electrons, the greater the forces, and so the higher the melting/boiling point
  • Halogens are all in the p block as their highest energy electron is in the p shell (all end in p5)
  • They are all oxidising agents (electron acceptors)
• Oxidation of halogens


  X2 + 2e- -> 2X-
• Disproportionation


  Simultaneous oxidation and reduction of the same species
• Disproportionation reactions


  • Blue litmus is turned red in chlorine water
  • Chlorine is reacts with water to form hydrochloric and chloric (I) acid
  • Chlorine is added to water in tiny amounts to kill the bacteria (such as the bacteria that cause cholera)
  • Chlorine reacts with organic compounds to form halogenated organic molecules, which are carcinogenic
  • Chlorine can be reacted with cold, aqueous sodium hydroxide to produce Salt (NaCl), Bleach (NaOCl- sodium chlorate 1) and water
  • Chlorine can also be reacted with hot concentrated sodium hydroxide, which produces Salt, water, and Sodium chlorate (V)
• Elements in a period have the same number of atomic orbitals


  There is decreasing oxidising power down the group
• Oxidising power of halogens

  • Chlorine has more oxidising power than bromine because it has a smaller atomic radius and less shielding, which outweigh its lesser nuclear charge
• Displacement reactions of halogens

  1. Chlorine and aqueous potassium bromide-> yellow solution, orange bromine layer (Br2) can be separated out by cyclohexane

  2. Bromine appears yellow in water as it is non-polar, so doesn't dissolve well in polar substances (aqueous), dissolves well in cyclohexane as it is non-polar and can form van der waal forces with the cyclohexane and fully dissolve into it, allowing it to be its true colour

  3. The next reaction is between chlorine and aqueous iodide ions, the solution turns brown, and the cyclohexane layer goes violet/purple, showing iodine has been displaced

  4. Bromine and aqueous iodide react to form a brown aqueous solution, and a purple cyclohexane layer, showing that iodine has been displaced

  5. Iodine and aqueous chloride ions do not react as iodine cannot displace chlorine