Chlorine
Chlorine Cl is an element of period 3, the main subgroup of group VII, atomic number 17, shells 2, 8, 7; its molecule Cl₂ has a nonpolar covalent bond (Cl–Cl). In nature it occurs only in compounds: rock salt NaCl, sylvite KCl, carnallite and others. In industry chlorine is made by electrolysis of a salt solution: 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂. Chlorine is a yellowish-green, sharp-smelling, choking, poisonous gas; about 2.5 times heavier than air, partly soluble in water (chlorine water). Being a strong oxidizing agent it reacts with sodium 2Na + Cl₂ → 2NaCl, with iron 2Fe + 3Cl₂ → 2FeCl₃ (Fe is oxidized to +3) and with hydrogen H₂ + Cl₂ → 2HCl. With water and alkali one atom is the oxidizing and the other the reducing agent: Cl₂ + H₂O → HCl + HClO. Chlorine is used to disinfect drinking water, bleach cloth, and make plastics and hydrochloric acid. Only a teacher or specialist works with chlorine in a fume cupboard; it must never be smelled.
“Chlorine safety poster”: on A3 paper draw and write chlorine’s properties, uses and safety rules (goggles, gloves, fume cupboard, never smell, hazard sign). No experiment with chlorine is done at home, and cleaning products (chlorine bleach) are never mixed.