What is Chlorine atom?

     

Chlorine is a chemical element with the symbol Cl and atomic number 17.  The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them.  Chlorine is a yellow-green gas at room temperature.  It is an extremely reactive element and a strong oxidising agent; among the elements, it has the highest electron affinity and the third-highest electronegativity on the pauling scale, behind only oxygen and fluorine. 

     The most common compound of chlorine, sodium chloride (common salt), has been known since ancient times.  Around 1630,chlorine gas was first synthesised in a chemical recognised  as a fundamentally important substance.  Carl Wilhelm Scheele wrote a description of chlorine gas in 17 supposing it to be an oxide of a new element.  In1809, chemists suggested that the gas might be a pure element, and this was confired by Sir Humhry Davy in 1810 who named it form Ancient Greek;'pale green' based on its colour.

     Because of its great reactivity, all chlorine in the Earth's crust is in the form of ionic chloride compounds, which includes table salt.  It is the second-most abundant halogen and twenty-first most abundant chemical element in Earth's crust.  These crustal deposits are nevertheless dwarfed by the huge reserves of chloride in seawater. 

     In the form of chloride ions, chlorine is necessary to all known species of life.  Other types of chlorine compounds are rare in living organisms, and artificially produced chlorinated organics range from inert to toxic.  In the upper atmosphere, chlorine-containing organic molecules such as chlorofluorocarbons  have been implicated in ozone depletion.  Small quantities of elemental chlorine are generated by oxidation of chloride to hypochlorite in neutrophils as part of an immune system response against becteria.