Halogens

• The boiling points of Cl, Br and I increases as you go down the group because there are more electrons, stronger London forces so more energy is needed to break the intermolecular forces
• The electron configuration of group 7 is s2, p5
• Reactivity decreases in the reactions of Cl, Br, I with halide ions because the atomic radius increases, shielding increases and there is less nuclear attraction
• Cl is pale green in both water and cyclohexane
• Br is brown in water and orange in cyclohexane
• I is brown in water and is purple in cyclohexane
• Disproportionation in the reaction of chlorine with water is that chlorine is both oxidised and reduced
• The benefits of using chlorine in water treatment is that it kills bacteria and makes water safe to drink and without it, waterborne diseases would break out like cholera
• The risks of using chlorine in water treatment is that the chlorine can react with hydrocarbons which can cause cancer
• Precipitation reactions with aqueous silver ions is how to test for Cl-, Br- and I- ions