Chlorine and Iodine

Both are part of the Halogen Group (Group 7) on the periodic table.
Chlorine
- It’s a greenish-yellow gas at room temperature which is poisonous if inhaled.
- It has a strong oxidising ability.
- It forms acidic solutions in water.
Iodine
- It’s a dark grey solid at room temperature which can sublimate directly to a violet vapour when heated
- It’s less reactive than chlorine.
- It also forms acidic solutions in water.
Both chlorine and iodine will form salts with metals.
Displacement reactions involving halogens are determined by the reactivity of the halogen: A more reactive halogen will displace a less reactive halogen from its compounds. For example, chlorine can displace iodide ions (from an iodide salt solution), but iodine cannot displace chloride ions (from a chloride salt solution).
Test for halides: add dilute nitric acid followed by silver nitrate solution. Chloride ions give a white precipitate of silver chloride, while iodide ions give a yellow precipitate of silver iodide.
Uses: Chlorine is used in water treatment and manufacturing a wide range of consumer products. Iodine is used as a disinfectant, in photography and in the treatment of thyroid conditions.
Key points to remember: reactivity in group 7 decreases down the group, therefore Chlorine is more reactive than Iodine. Test results in a displacement reaction can show this.