Substance simple, gazeuse, d'un jaune verdâtre, et d'une odeur suffocante (symbole : Cl, nombre atomique 17).
Sinonimi: Cl | atomic number 17
ETYM Greek, pale green, greenish yellow. So named from its color.
A common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent; occurs naturally as a salt (as in sea water); SYN. Cl, atomic number 17.
Greenish-yellow, gaseous, nonmetallic element with a pungent odor, symbol Cl, atomic number 17, atomic weight 35.453. It is a member of the halogen group and is widely distributed, in combination with the alkali metals, as chlorates or chlorides.
In nature it is always found in the combined form, as in hydrochloric acid, produced in the mammalian stomach for digestion. Chlorine is obtained commercially by the electrolysis of concentrated brine and is an important bleaching agent and germicide, used for both drinking and swimming-pool water. As an oxidizing agent it finds many applications in organic chemistry. The pure gas (Cl2) is a poison and was used in gas warfare in World War I, where its release seared the membranes of the nose, throat, and lungs, producing pneumonia. Chlorine is a component of chlorofluorocarbons (CFCs) and is partially responsible for the depletion of the ozone layer; it is released from the CFC molecule by the action of ultraviolet radiation in the upper atmosphere, making it available to react with and destroy the ozone. Chlorine was discovered 1774 by the German chemist Karl Scheele, but English chemist Humphry Davy first proved it to be an element 1810 and named it after its color.
Some typical reactions are given below.
When dry chlorine is passed over a heated metal, the chloride is formed.
Zn + Cl2 ® ZnCl2 2Fe + 3Cl2 ® 2FeCl3.
The same reaction occurs with certain nonmetals, when the dry gas is passed over the heated element.
2P + 5Cl2 ® 2PCl5.
With water, chlorine forms a bleaching solution.
H2O + Cl2 ® HCl + HOCl 2OCl- ® 2Cl- + O2.
Iron (II) salts are oxidized to iron (III) salts.
2FeCl2 + Cl2 ® 2FeCl3.
Organic compounds undergo halogenation.
C2H6 + Cl2 ® C2H5Cl + HCl C2H4 + Cl2 ® C2H4Cl2.
Alkalis form chlorides, chlorates, and water.
2NaOH + Cl2 ® NaCl + NaOCl + H2O.
Other halogens are displaced in a redox reaction.
2KBr + Cl2 ® 2KCl + Br2.