Group 7

• At room temperature, fluorine is a pale yellow gas.
• At room temperature, Chlorine is a green gas.
• At room temperature, bromine is a dark red volatile liquid or a brown vapour
• At room temperature, Iodine is a shiny black solid that sublimes to give purple vapour.
• Iodide is the best reducing agent as there is greater shielding between the positive nucleus and the electron that is being donated so it is more easily lost
• The reducing ability of the halogens increases down group 7
• Sulfur dioxide is a choking gas.
• Hydrogen sulfide smells like rotten eggs.
• Boiling point of the halogens increase down the group.
• Chlorine reacts with water in a reversible reaction producing a mixture of HCl and chlorate (I) acid (ClO- is the chlorate ion). The mixture is pale green and referred to as chlorine water.
• Give the reversible reaction equation for chlorine and water

  Cl2 (g) + H2O (l) ⇌ HCl (aq) + HClO (aq)
• The reaction between chlorine and hot water is different:

  2 Cl2 (g) + 2 H2O (l) --> 4 HCl (aq) + O2 (g)
• The reaction between chlorine and cold dilute sodium hydroxide:

  Cl2 (g) + 2NaOH (aq) ⇌ NaCl (aq) + NaClO (aq) + H2O (l)

  This is a disproportionate reaction
• The halogens can act as oxidising agents, and this decreases down the group.
• The halide ions can act as reducing agents. This increases down the group.
• As reducing ability increases down the group, the halides can further decrease the oxidation state of sulphur from +6 in H2SO4 to -2 in H2S.
• Chloride ion plus sulphuric acid:

  NaCl + H2SO4 → NaHSO4 + HCl

  Misty fumes of HCl is prodced, not a redox reaction. Chloride ion is too weak to to reduce the sulphur.
• Bromide ions plus sulphuric acid:

  NaBr + H2SO4 → NaHSO4 + HBr

  Brown fumes of bromine are also produced, as is colourless sulphur dioxide gas (choking gas)

  Bromide ions are strong enough to reduce the sulphur to +4 in sulphur dioxide.
• Iodide ions plus sulphuric acid

  NaBr + H2SO4 → NaHSO4 + HBr

  Also, a black solid of iodine, purple gas of iodine, and bad egg smell of hydrogen sulphide gas are observed. May also produce solid sulphur and sulphur dioxide.

  Iodide ions are strong enough to reduce sulphur from +6, to +4, to 0, to -2.