Chlorine

Chlorine (from the Greek language Chloros, meaning "pale green"), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17. As part of common salt and other compounds, it is abundant in nature and necessary to most forms of life, including the human body. As chlorine gas, it is greenish yellow, is two and one half times as heavy as air, has an intensely disagreeable suffocating odor, and is exceedingly poisonous. In its liquid and solid form it is a powerful oxidizing, bleaching, and disinfecting agent.

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*10-15 to 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.

Related Topics:
Isotope - Atom - Radioactive - Spallation - Ar - Cosmic ray - Proton - Neutron capture - Muon capture - Ca - S - Half-life - Hydrophilic - Geologic dating - Seawater - Nuclear weapon - Soil - Ground water

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