Group 7

• The group 7 elements are highly reactive non-metals that react to form a 1- ion to achieve a full outer shell.
• The atomic radius increases down the group due to addition electron shells.
• Reactivity decreases down the group as nuclear attraction becomes weaker due to increased shielding and distance so it becomes more difficult to attract an electron.
• Ionisation energy decreases down the group due to a greater atomic radius and increased shielding.
• Melting point increases down the group as group 7 elements are simple covalent molecules and the strength of the van der waals forces between them increase with increased Ar.
• Oxidising power decreases down the group as their ability to attract electrons decreases.
• A halogen will displace any halide beneath it in the periodic table.
• Halide ions are good reducing agents, and this increases down the group as electrons are easier to lose.
• All halide ions can react with sulfuric acid as a sodium halide to form sodium hydrogen sulfate and and a hydrogen halide (NaX + H2SO4 -> NaHSO4 + HX).
• Halide ions from bromine down can react with sulfuric acid as a hydrogen halide to form a halogen, sulfur dioxide and water (2 HX + H2SO4 -> X2 + SO2 + 2 H2O).
• Halide ions from iodine down can react with sulfur dioxide as a hydrogen halide to form a halogen, hydrogen sulfide and water (6HX + SO2 -> H2S + 3 X2 + 2 H2O).
• The greater the reducing power of a halide, the longer the reaction with H2SO4 as the halide can reduce more species.
• Acidified silver nitrate and ammonia are used to test for halide ions.
• In acidified silver nitrate, Cl- forms a white precipitate, Br- forms a cream precipitate and I- forms a yellow precipitate.
• In dilute NH3, Cl- dissolves but Br- and I- don't.
• In conc. NH3, CL- and Br- dissolves, but I- doesn't.
• Chlorine reacts with cold water to produce chlorate (I) ions (ClO-), Cl- ions and H+ ions. This is a disproportionation reaction as the chlorine is both oxidised and reduced.
• In the presence of UV light, chlorine decomposes water to produce oxygen and hydrochloric acid. The chlorine is reduced.
• Chlorine is toxic and an irritant but is used to kill bacteria in water treatment processes as the benefits outweigh the risks.
• Chlorine can be mixed with cold, aqueous sodium hydroxide to produce sodium hypochlorite (NaCLO), a key ingredient in bleach, as well as sodium chloride and water.