Tellurium - chemistry.

Tellurium - chemistry. I INTRODUCTION Tellurium (Latin tellus, "earth"), symbol Te, silver-white, brittle, semimetallic element. The atomic number of tellurium is 52. Tellurium was first discovered in 1782 by the German scientist Franz Joseph Müller von Reichenstein; it was recognized as an element and given its name in 1798 by the German chemist Martin Heinrich Klaproth. II PROPERTIES AND OCCURRENCE Tellurium is a comparatively stable element, insoluble in water and hydrochloric acid but soluble in nitric acid and aqua regia. Tellurium reacts with an excess of chlorine to form tellurium dichloride, TeCl2, and tellurium tetrachloride, TeCl4. It is oxidized by nitric acid to produce tellurium dioxide, TeO2, and by chromic acid to produce telluric acid, H2TeO4. In combination with hydrogen or certain metals, it forms tellurides such as hydrogen telluride, H2Te, and sodium telluride, Na2Te. Tellurium melts at about 450°C (about 842°F), boils at about 988°C (about 1810°F), and has a specific gravity of 6.25. The atomic weight of tellurium is 127.60. Tellurium is quite rare; it ranks about 78th in natural abundance among the elements in Earth's crust. It occurs in the pure state or is found in combination with gold, silver, copper, lead, and nickel in such minerals as sylvanite, petzite, and tetradymite. Occasionally it is found in rocks as tellurite (or tellurium dioxide), TeO2. The slime from lead and copper refineries and the flue dust from telluride-gold deposits are the principal commercial sources. It is also prepared by reduction of telluric oxide, forming a grayish-white, metallic powder. Tellurium deposits are found in Mexico, South America, western Australia, and Ontario, Canada. In the United States, small amounts of the element are obtained from rocks in Colorado and California. III USES Tellurium is used in the manufacture of rectifiers and thermoelectric devices and in semiconductor research. With other organic substances, it is employed as a vulcanizing agent in the processing of natural and synthetic rubber; and in antiknock compounds for gasoline. It is used also to impart a blue color to glass. Colloidal tellurium is an insecticide, germicide, and fungicide. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.