Chlorine
The most common compound of chlorine, sodium chloride, has been known since ancient times. Around 1630 chlorine gas was first synthesized in a chemical reaction, but not recognized as a fundamentally important substance. Characterization of chlorine gas was made in 1774 by Carl Wilhelm Scheele, who supposed it 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 from Ancient green".
Nearly all chlorine in the Earth's crust occurs as chloride in various ionic compounds, including table salt. It is the second most abundant halogen and 21st most abundant chemical element in Earth's crust. Elemental chlorine is commercially produced from brine by electrolysis. The high oxidizing potential of elemental chlorine led commercially to free chlorine's bleaching and disinfectant uses, as well as its many uses of an essential reagent in the chemical industry. Chlorine is used in the manufacture of a wide range of consumer products, about two-thirds of them organic chemicals such as polyvinyl chloride, as well as many intermediates for production of plastics and other end products which do not contain the element. As a common disinfectant, elemental chlorine and chlorine-generating compounds are used more directly in swimming pools to keep them clean and sanitary.
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 the immune response against bacteria. Elemental chlorine at high concentrations is extremely dangerous and poisonous for all living organisms, and was historically used in World War I as the first gaseous chemical warfare agent.
Occurrence
In the interstellar medium, chlorine is produced in supernovae via the r-process.
In meteorites and on Earth, chlorine is found primarily as the chloride ion which occurs in minerals. In the Earth's crust, chlorine is present at average concentrations of about 126 parts per million, predominantly in such minerals as halite (sodium chloride), sylvite (potassium chloride), and carnallite (potassium magnesium chloride hexahydrate).
Chloride is a component of the salt that is deposited in the earth or dissolved in the oceans — about 1.9% of the mass of seawater is chloride ions. Even higher concentrations of chloride are found in the Dead Sea and in underground brine deposits. Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground.
Over 2000 naturally occurring organic chlorine compounds are known.
| Symbol | Cl | |
| Atomic Number | 17 | |
| Atomic Weight | 35.4527 | |
| Oxidation States | +1,+5,+7,-1 | |
| Electronegativity, Pauling | 3.16 | |
| State at RT | Gas, Nonmetal | |
| Melting Point, K | 172.2 | |
| Boiling Point, K | 238.6 |
Interesting Facts about Chlorine
- The first chain reaction discovered was not a nuclear reaction; it was a chemical chain reaction. It was discovered in 1913 by Max Bodenstein, who saw a mixture of chlorine and hydrogen gases explode when triggered by light. The chain reaction mechanism was fully explained in 1918 by Walther Nernst.
- Earth’s oceans contain a large amount of chlorine. If this chlorine were released as a gas, its weight would be 5x greater than Earth’s total current atmosphere. (Our oceans contain about 2.6 x 1016 metric tons of chlorine, mostly as sodium chloride.)
- Chlorine is not only abundant in our oceans; it is the sixth most abundant element in Earth’s crust.
- Exposure to small amounts of chlorine, even for a short time, can be deadly. Fatalities are expected at 1 part in a thousand chlorine in air (or sometimes at even lower concentrations).
- Chlorine is heavier than air. When released, it forms a poisonous blanket that drifts along with the wind. Chlorine was used as a chemical weapon in World War I, first in 1915 by the German army and then by the Western Allies. It was not as ‘effective’ as had been hoped, because chlorine is easily detected by its strong smell. It is also water soluble, and so soldiers could protect themselves from the worst of its effects by breathing through damp cloths.
Appearance and Characteristics
Harmful effects:
Chlorine is a toxic gas that irritates the skin, the eyes and the respiratory system.
Characteristics:
- Chlorine is a greenish-yellow, diatomic, dense gas with a sharp smell (the smell of bleach).
- It is not found free in nature as it combines readily with nearly all other elements.
- Chlorine occurs in nature mainly as common salt (NaCl), carnallite [ KMgCl2.6(H20) ], and sylvite (KCl).
- In its liquid and solid form it is a powerful bleaching, oxidizing and disinfecting agent.
Uses of Chlorine
- Chlorine is used for producing safe drinking water.
- Chlorinated compounds are used mostly for sanitation, pulp bleaching, disinfectants, and textile processing.
- Chlorine is also used for the manufacture of chlorates and it is important in organic chemistry, forming compounds such as chloroform, carbon tetrachloride, polyvinyl chloride, and synthetic rubber.
- Other uses of chlorine compounds include dyestuffs, petroleum products, medicines, antiseptics, insecticides, foodstuffs, solvents, paints and plastics.
Sodium Choride is table salt. You’ve run out? Here’s one way of getting more!
Chlorine made by reacting hydrochloric acid with potassium permanganate
