Chlorine is a chemical element; it has 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 revised Pauling scale, behind only oxygen and fluorine.
Chlorine played an important role in the experiments conducted by medieval alchemists, which commonly involved the heating of chloride salts like ammonium chloride (sal ammoniac) and sodium chloride (common salt), producing various chemical substances containing chlorine such as hydrogen chloride, mercury(II) chloride (corrosive sublimate), and aqua regia. However, the nature of free chlorine gas as a separate substance was only recognised around 1630 by Jan Baptist van Helmont. Carl Wilhelm Scheele wrote a description of chlorine gas in 1774, supposing it to be an oxide of a new element. In 1809, chemists suggested that the gas might be a pure element, and this was confirmed by Sir Humphry Davy in 1810, who named it after the Ancient Greek χλωρός (khlōrós, "pale green") because of 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 (after fluorine) and 20th most abundant element in Earth's crust. These crystal deposits are nevertheless dwarfed by the huge reserves of chloride in seawater.
Keywords
1774 supposing
chlorine gas
huge reserves
crystal deposits
earths crust
great reactivity
pure element
1809 chemists suggested
separate substance
aqua regia
chemical substances
chloride salts
commonly involved
medieval alchemists
experiments conducted
important role
thirdhighest electronegativity
room temperature
yellowgreen gas
atomic number 17
symbol cl
chemical element
abundant element
periodic table
fluorine chlorine played
free chlorine gas
ionic chloride compounds
extremely reactive element
secondmost abundant halogen
includes table salt
sir humphry davy
revised pauling scale
highest electron affinity
strong oxidising agent
