Encyclopedia > Cl

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17. Chlorine gas is greenish yellow, is two and one half times as heavy as air, has an intensely disagreeable suffocating odor, and is exceedingly poisonous. It is a powerful oxidizing, bleaching[?], and disinfecting agent. As part of common salt and other compounds, it is abundant in nature and necessary to most forms of life.

Table of contents

1 Notable Characteristics

2 Applications

3 History

Notable Characteristics The pure chemical element has the physical form of a diatomic green gas. The name chlorine is derived from chloros, meaning green, referring to the color of the gas.

This element is a member of the salt-forming halogen series and is extracted from chlorides through oxidation and more commonly, by electrolysis. Chlorine is a greenish-yellow gas that combines readily with nearly all other elements. At 10 °C one liter of water dissolves 3.10 liters of chlorine and at 30 °C only 1.77 liters. Applications Chlorine is an important chemical in water purification, in disinfectants[?] in bleach and in mustard gas.

Chlorine is also used widely in the manufacture of many everyday items.

Used to kill bacteria and other microbes from drinking water supplies. Even small water supplies are now routinely chlorinated.
Used widely in paper product production, antiseptic, dyestuffs, food, insecticides, paints, petroleum products, plastics, medicines, textiles, solvents, and many other consumer products.

Organic chemistry uses this element extensively as an oxidizing agent and in substitution because chlorine often imparts many desired properties in an organic compound when it is substituted for hydrogen (synthetic rubber[?]).

Others uses are in the production of chlorates, chloroform, carbon tetrachloride, and in the bromine extraction. History Chlorine (Gr. chloros, greenish yellow) was discovered in 1774 by Carl Wilhelm Scheele, who mistakenly thought it contained oxygen. Chlorine was give its name in 1810 by Humphry Davy, who insisted that it was in fact an element. Occurrence Chlorine is manufactured by electrolysis of an aqueous solution of sodium chloride.

In nature it is only found combined with other elements chiefly sodium in the form of common salt (NaCl), but also in carnallite[?], and sylvite[?]. Compounds Chlorides Chlorites Chlorates[?] Perchlorates[?] Isotopes There are two principal stable isotopes of chlorine, of mass 35 and 37, found in the relative proportions of 3:1 respectively, giving chlorine atoms in bulk an apparent atomic weight of 35.5. Chlorine has 9 isotopes with mass numbers ranging from 32 to 40. Only three of these isotopes occur naturally: stable Cl-35 (75.77%)and Cl-37 (24.23%), and radioactive Cl-36. The ratio of Cl-36 to stable Cl in the environment is about 700 E -15 : 1. Cl-36 is produced in the atmosphere by spallation[?] of Ar-36 by interactions with cosmic ray protons. In the subsurface environment, Cl-36 is generated primarily as a result of neutron capture[?] by Cl-35 or muon capture[?] by Ca-40. Cl-36 decays to S-36 and to Ar-36, with a combined half-life of 308,000 years. The half-life of this hydrophilic nonreactive isotope makes it suitable for geologic dating[?] in the range of 60,000 to 1 million years. Additionally, large amounts of Cl-36 were produced by irradiation of seawater[?] during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of Cl-36 in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water[?], Cl-36 is also useful for dating waters less than 50 years before the present. Cl-36 has seen use in other areas of the geological sciences, including dating ice and sediments. Precautions Chlorine irritates respiratory systems especially in children and the elderly. In its gaseous state it irritates mucus membranes[?] and when a liquid it burns skin. It takes as little as 3.5 ppm to be detected as distinct odor but it takes 1000 ppm or more to be fatal. Because of this, chlorine was one ot the gases used during World War I as a war gas.

Exposure to this gas should therefore not exceed 0.5 ppm (8-hour time-weighted average - 40 hour week.).

Acute exposure to high (but non-lethal) concentrations of Chlorine can result in Pulmonary Edema, or fluid in the lungs, an extremely unpleasant condition. Chronic low-level exposeure weakens the lungs, increasing susceptibility to other lung disorders.

Chlorine gas can be formed when bleach is mixed with urine or with another cleaning product; therefore these combinations should be avoided.