3.1.3 - the halogens

• Group 7 elements are referred to as the halogens
• Halogens exist as diatomic molecules and have low melting and boiling points
• Boiling point increases down group 7 because:

  number of electrons of the atoms increases, so there are stronger london forces and more energy is required to overcome the forces
• Oxidising ability decreases down a group with Cl being the strongest and I being the weakest
• Oxidising ability decreases down a group because Cl has the fewest occupied electron shells, greatest force of attraction between outer electrons and nucleus and thus is the easiest to gain electrons and be reduced.
• Reducing ability increases down the group with Cl- being the weakest and I- being the strongest
• Reducing ability increases down the group because I- has the most occupied electron shell so outer electrons are further from the nucleus, weakest force of attraction so is most easily oxidised.
• Chlorine displaces both bromine and iodine

  bromine displaces iodine

  iodine doesnt displace either
• at room temp chlorine is a pale green gas
• At room temp fluorine is a pale yellow gas
• At room temp iodine is a dark grey solid
• As a gas, iodine is a purple gas
• In water, chlorine is pale green
• In water bromine is orange
• In cyclohexane chlorine is pale green
• In cyclohexane bromine is orange
• In cyclohexane iodine is violet
• The ionic equation for chlorine oxidising bromine atoms is:

  Cl2 (aq) + 2Br- (aq) —> 2Cl- (aq) + Br2 (aq)
• The ionic equation for chlorine oxidising iodine is:

  Cl2 (aq) + 2I- (aq) —> 2Cl- (aq) + I2 (aq)
• The ionic equation for bromine oxidising iodide ions is:

  Br2 (aq) + 2I- (aq) —> 2Br- (aq) + I2 (aq)
• The equation for the reaction of Cl2 with water:

  Cl2 (g) + H2O (l) —> HClO (aq) + HCl (aq)
• The reaction of chlorine with water is a Disproportionation reaction where chlorine is both oxidised and reduced
• Chlorine is added to drinking water as it kills bacteria in the water making it safer to drink

  os it is involved in the purification of water
• the chemical formula of bleach is NaClO
• The equation for forming bleach is:

  Cl2 (aq) + 2NaOH (aq) —> NaCl (aq) + NaClO (aq) + H2O (l)
• The two forms of the chlorate ion are

  ClO- chlorate (I)

  ClO3- chlorate (V)