What is chlorine?

The element chlorine (Cl) is one of the 92 natural elements found on our planet. Have you ever heard of 'Mendelev's Table'? Well, officially this table is called Periodic Table of the Elements. It shows all today's known chemical elements. As such, you'll find chlorine in the 17th column of this famous Table. Chlorine gas was first isolated in 1774 by the Swedish-German chemist, C. W. Scheele.
More information about C. W. Scheele on chemistryexplained.com

Is the element chlorine abundant? Yes. Only 16 elements constitute 99,6% of the earth crust. In this group of elements, chlorine ranks 11th. Chlorine is one of the most common elements in nature. Chlorinated compounds occur naturally in humans and are found in blood, skin and teeth. Even white blood cells need chlorine to enable them to fight off infections. In nature, chlorine is more plentiful than carbon. It occurs in both plants and animals and makes up 2.9% of the world's oceans and 0.045% of the earth's crust.

Scientists have identified more than 2,000 naturally-occurring chlorine-based compounds. These perform a range of useful functions in a wide range of organisms, from the Ecuadorian tree frog to Mediterranean jellyfish and from wood-rotting fungi to tropical sea slugs.

At room temperature, the molecule chlorine (Cl₂) is a greenish gas or (when pressurized) green liquid (see picture). You will never find it as such in nature, because it is highly reactive. Instead, all the chlorine we find on the planet is bound in compounds, like naturally-occurring organochlorine compounds and salts. Kitchen salt (which is sodium chloride) is the best example. Plain good old salt, dissolved in water to give brine, is the source we produce chlorine gas (Cl₂) from.

Where do we get our salt from?

About 50 quadrillion tonnes of dissolved sodium chloride (common salt) are found in the world's oceans and seas. However, less than a third of salt production stems from seawater. The majority comes from rock saltmines hundreds of meters below the surface of the Earth.
Read more about how we dig the salt up.

What do we use chlorine for?

Today, chlorine is used in a vast range of processes to create thousands of often indispensable products that serve our everyday needs at work, home and play. Examples include pharmaceuticals, medical devices, windows, flooring and insulation material and pipes, pure silicon for the production of photovoltaic cells. Water and swimming pool disinfection are of course the best-known applications, although they only account for a very modest percentage of total chlorine production.
Read more about uses of chlorine.

Chlorine's co-product caustic soda is essential in many industrial applications, among which the production of useful organic chemicals (more than 30 % of caustic production goes into this application), inorganic chemicals like paints, glass and ceramic, fuel cell production, cosmetics, the paper, pulp and cellulose industries, the food industry, soaps and detergents, textiles, aluminum production and rubber recycling.
Read more about the uses of caustic soda.

Is there a 'chlorine family'?

Yes: chlorine belongs to a group of five chemicals called ' halogens': fluorine, chlorine, bromine, iodine and astatine. The word 'halogen' originates from Greek roots: hal means 'salt' and gen means 'to produce'. All the chemicals in this group produce sodium salts with similar properties. The best known is of course sodium chloride (common salt).

Last update : 02/2012