Chlorine is a poisonous greenish-yellow gas with a strong, bad smell. In nature, it can only be found together with other elements, especially in minerals. Together with sodium it forms salt (NaCl).

Chlorine is used to make water clearer and purer. In swimming pools, it kills bacteria. We also use chlorine to clean metal. The industry uses chlorine compounds to produce paper, plastic, medicine and paint.

Chlorine often combines with other elements because it easily accepts free electrons from them. It has 17 protons and an atomic mass of 35.