The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
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The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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Most students of chemistry study the first four members of the halogen family-- fluorine, chlorine, bromine, and iodine --but hear little or nothing about the last member, astatine. Chemists searched long and hard for this element in nature, but without success. Finally, the element was created artificially in 1940 by D. R. Corseon, K. R. MacKenzie (b.1912), and Emilio Segrè working at the University of California at Berkeley. These scientists bombarded bismuth with alpha particles to obtain element #85. They named their discovery astatine (chemical symbol: At) after the Greek word for unstable, astatos.
Astatine is the only halogen with no stable isotopes. Of the 24 isotopes known, the two most stable have half lives of about 8 hours. Because it decays so rapidly, there may be no more than about 25 grams of the element in the Earth's crust.
Astatine appears to have the properties expected of the heaviest halogen element. It is a solid with a melting point of 302°C and an estimated boiling point of 337°C. It is more metallic than iodine and, according to some chemists, should be classified as a metalloid rather than as a non-metal. Definitive information about the element is somewhat difficult to obtain since scientists must work with samples weighing less than a microgram.
One interesting discovery is that astatine appears to behave like iodine in the human body, accumulating in the thyroid. Scientists speculate that, because it is so radioactive, the element might be used to treat hyperthyroidism. When given to a person with an overactive thyroid gland, the element may go to the thyroid and destroy some excess thyroid tissue by irradiation.