I.

Introduction

Chlorine, symbol Cl, greenish-yellow gaseous element. In group 17 (or VIIa) of the periodic table, chlorine is one of the halogens. The atomic number of chlorine is 17.

Chlorine was first isolated in 1774 by the Swedish chemist Carl Wilhelm Scheele, who thought that the gas was a compound; it was not until 1810 that the British chemist Sir Humphry Davy proved that chlorine was an element and gave it its present name.