Chlorine

Chlorine belongs to the halogen family and reacts readily with many other elements. At room temperature, it is a yellow-green, poisonous gas. In nature, chlorine is found mainly as chloride in compounds, including sodium chloride, the familiar table salt. Huge amounts of chloride are dissolved in seawater, and chloride salts also form underground deposits. Industry produces chlorine by electrolysis of brine: electricity drives chemical reactions in concentrated salt water, releasing chlorine gas. Chlorine and certain chlorine compounds are used to disinfect water, while much industrial chlorine goes into making PVC plastic. The contrast is striking: chlorine gas is toxic, but chloride ions are essential for life.