Uranium
Uranium is a actinide series, rare earth element denoted by the atomic symbol, U. It has an atomic number of 92 and the atomic weight of its isotopes is 238.0289. The element is a silvery-white, lustrous metal with a melting point of 3070° F (1132.3° C) and a boiling point of 6904° F (3818° C). Three naturally occurring isotopes of the element exist; uranium-238 is by far the most abundant (99.276%), followed by uranium-235 (0.718%) and uranium-234 (0.0056%). Another eleven isotopes, all radioactive, have been produced artificially. Uranium-238 and uranium-235 are the first members of radioactive decay families. Each isotope decays to produce a daughter isotope, which is also radioactive and that also decays to produce another daughter isotope. This process is repeated about a dozen times in each case until a stable isotope results.
Uranium has been said to be the metal that has changed the face of modern civilization. Evidence suggests that It was probably used as far back as a.d. 79. Green glass taken from a Roman mural and dated to that period contains about 1 percent uranium oxide. Archaeologists believe that the oxide was intentionally added to color the glass. Ancient technicians certainly had no understanding of the chemical nature of the material with which they were working. In fact, the existence of uranium and its compounds was not acknowledged until the late 1700s. Before that time, most chemists thought that pitchblende, the most common ore of uranium, was an ore of iron and zinc.
In 1789, however, Martin Heinrich Klaproth analyzed pitchblende and obtained an unfamiliar yellow powder. He guessed that it contained a new element, which he named uranium in honor of the newly discovered planet, Uranus. By heating the yellow powder with charcoal, he hoped to obtain the pure metal. The black, lustrous powder he obtained in the reaction looked like the product he expected and was acknowledged as the pure element for over half a century.
Then, in 1841, the French chemist, Eugène-Melchior Peligot, proved that Klaproth's black powder was an oxide of uranium and not the pure metal itself. Peligot heated uranium chloride with potassium metal, a method that proved successful. He obtained another black powder that looked like Klaproth's but that had very different properties. It was, in fact, almost pure uranium.
Uranium was of relatively little interest until 1896, when Henri Becquerel discovered that pitchblende emitted a form of radiation similar to that of X-rays. Further research showed that the radioactivity was produced by uranium and related elements in the pitchblende. The discovery opened a new era in chemistry and physics that was to transform not only the sciences but the whole of human society as well.
Uranium is found naturally in minerals such as pitchblende, uraninite, carnotite, and autunite. It is mined from a variety of sources. It is purified by a reduction reaction with alkaline earth metals or by electrolysis.
The discovery of nuclear fission in the late 1930s revealed a special property of the uranium-235 isotope. When bombarded with neutrons, the atomic nucleus of uranium-235 splits into two roughly equal parts and releases large amounts of energy and additional neutrons. This reaction has made it possible to use nuclear energy for peaceful purposes as well as for military applications.
Although uranium compounds were once used to a limited extent as toners in photography, as mordants in the dyeing of silk and wool, in color glazes, and in the leather industry, the element's most important uses today are all in the nuclear power industry. This is either in reactors at the core of nuclear power plants or in nuclear weapons.
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