2.3 Group 7

• The halogens are made up of nonmetals and are located on the right-hand side of the periodic table.
• The electron configuration of fluorine and chlorine is 1s2 2s2 2p5.
• Chlorine gas is pale green and has the electron configuration bb2.
• Bromine is a brownish-orange liquid and has the electron configuration bb2.
• Iodine has a much longer electron configuration but it's just to give you an idea.
• Group two ions can be identified using flame tests, where a solid sample is placed on a nichrome wire and dipped into a Bunsen flame.
• Sulfates can be identified using barium chloride, where if sulfates are present, a white precipitate will form.
• Silver nitrate solution and nitric acid are used to identify compounds, where if a compound contains silver ions, a white precipitate will form.
• Ammonium compounds can be identified using litmus paper, where a suspected ammonium compound is added to sodium hydroxide and if ammonia gas is produced, the litmus will turn blue.
• Carbonates can be identified using hydrochloric acid, where if a carbonate is present, carbon dioxide gas will be given off.
• Hydroxides are alkaline and will turn red litmus blue.
• As we go down the group from fluorine to iodine, the boiling point increases because the molecules and the size of the atoms and the molecules are getting larger, resulting in larger van der Waals forces and requiring a higher amount of energy to turn these into the gas.
• The nitric acid is added to the ammonia solution to mop up any rogue carbonates that could precipitate out.
• The overall ionic equation is I- → I2 and sulfuric acid → solid silver and iodine ions.
• The ammonia is added to the silver nitrate solution to test for carbonates.
• The reaction with silver nitrate and ammonia is used to test for chlorides, bromides, and iodides.
• The nitric acid is added to the silver nitrate solution to react with any other halides that could precipitate out.
• The ammonia is added to the silver nitrate solution to test for halides.
• The nitric acid is added to the ammonia solution to mop up any rogue halides that could precipitate out.
• Lance water with protons and electrons, resulting in a solid silver and iodine ions.
• The electronegativity decreases as we go down the group because the ability for one of these atoms to attract electrons towards itself weakens and the atoms get larger and the distance between the positive nucleus and the bonding electrons increases, resulting in more shielding.
• Sodium bromide and sodium iodide are not as powerful reducing agents as chloride, so they cannot reduce sulfur any further.
• Sodium bromide and sodium iodide can also react with concentrated sulfuric acid to produce other products.
• Chlorides, bromides, and iodides can reduce sulfur further to produce sulfur dioxide.
• Sodium bromide and sodium iodide can reduce sulfur to produce sulfur dioxide and bromine or iodine.
• Sodium hydrogen sulfate produced in these reactions can further react with concentrated sulfuric acid to form other products.
• Reduction products of sulfuric acid include sodium hydrogen sulfate, which is not a reduction product.
• Chlorides, bromides, and iodides all produce sodium hydrogen sulfate when reacted with concentrated sulfuric acid.
• Iodide can reduce sulfur even further to produce sulfur.
• Displacement reactions are important in understanding the reactivity of halogens.
• A more reactive halogen will displace a less reactive halide ion.
• The reactivity of halogens decreases as we go down group 7.
• Bleach is used for water sterilization, as it kills bacteria and microbes that cause diseases like cholera.
• Bromine is more reactive than iodide ions, leading to a space for reaction and the formation of two BR- ions.
• Bleach is made by using a disproportionation reaction, where sodium hydroxide and chlorine form sodium chlorate one solution, also known as bleach.
• Chlorine has been simultaneously reduced and oxidized, a process known as disproportionation.
• In the absence of sodium hydroxide, chlorine and water form chlorine ions and ClO- ions, which are soluble and dissociate strongly.
• In swimming pools, sunlight can decompose chlorinated water, resulting in no CL- that kills the bacteria.
• Chlorine is more reactive than iodide ions, leading to a displacement reaction and a brown solution.
• Bromine is less reactive than chloride ions, resulting in no reaction.