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Metal Cation Identification
Information on CERIUM
- General Information
- Occurence Uses and Properties
- History of the Metal
- Compounds
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General Information
Cerium(Ce), chemical element, most abundant of the rare-earth metals of transition Group IIIb of the periodic table. Cerium is iron gray in colour and about as soft and ductile as tin. It oxidizes slowly in air, rapidly reacts with water to yield hydrogen, and burns brilliantly when heated. Cerium as the oxide (ceria) was discovered (1803) by Jöns Jacob Berzelius and Wilhelm Hisinger working together, and independently by Martin Klaproth. It was named after the asteroid Ceres, which was discovered in 1801.
atomic number = 58
atomic weight = 140.120
melting point = 798 C
boiling point = 3,257 C
specific gravity = 6.771 (25 C)
valence = 3, 4
electronic config. 2-8-18-20-8-2 or (Xe)4f 25d06s2
Occurrence, uses, and properties.
Ceria, the second rare earth to be discovered (yttria was first), turned out to be a mixture of oxides from which seven elements were separated during the course of the next century. These other elements were the lighter rare-earth metals, from lanthanum (atomic number 57) to gadolinium (atomic number 64), with the exception of promethium. Cerium occurs in monazite, bastnaesite, and many other minerals. It also is found among the fission products of uranium, plutonium, and thorium. Cerium is about as abundant as copper and nearly three times as abundant as lead in the igneous rocks of Earth's crust. Four stable isotopes occur in nature: cerium-140 (88.48 percent), cerium-142 (11.07 percent), cerium-138 (0.250 percent), and cerium-136 (0.193 percent). The metal itself is prepared by electrolysis of the anhydrous fused halides or by thermoreduction of the halides with alkali or alkaline-earth metals. It exists in four allotropic (structural) forms.
History.
In 1794, Johan Gadolin, a Finnish chemist, while investigating a rare Swedish mineral, discovered a new earth in impure form, which he believed to be a new element and to which he gave the name ytterbia, from Ytterby, the village where the ore was found. The name, however, was soon shortened to yttria. In 1803, from the same mineral, later named gadolinite in Gadolin's honour, another new earth was reported in the literature independently by several chemists. The new earth became known as ceria, from the asteroid Ceres, which had just been discovered (1801). Since yttria and ceria had been discovered in a rare mineral, and they closely resembled other known earths, they were referred to as the rare earths. Not until 1808 did Sir Humphry Davy demonstrate that the earths as a class were not elements themselves but were compounds of oxygen and metallic elements. Later, a number of chemists verified the existence of ceria and yttria in gadolinite and found that these oxides were also present in a wide variety of other rare minerals. The elements of which yttria and ceria were the oxides were then given the names yttrium and cerium, respectively.
Chemical Compounds.
Cerium and its compounds have a number of practical appliCATions. The dioxide is employed in the optics industry for fine polishing of glass (replacing rouge); it is also used as an opacifier in porcelain coatings and as a decolorizer in glass manufacturing. Cerium nitrate has been used in the manufacture of incandescent-gas mantles; other salts are employed in the ceramic, photographic, and textile industries. The metal serves as an ingredient in the carbon-impregnated arc lamps that have been used for illumination in the motion-picture, television, and related industries. Together with the other rare-earth metals, cerium is a constituent of numerous ferrous and nonferrous alloys; a superior high-temperature alloy for jet engines contains about 3 percent cerium with magnesium. Misch metal (50 percent cerium) is used for cigarette-lighter flints, in tracer bullets, and in electron-tube manufacture as a getter, which removes traces of oxygen.
Along with praseodymium and terbium, cerium is different from the other trivalent rare earths in that it forms compounds in which it is tetravalent; it is the only rare earth that exhibits a +4 oxidation state in solution. Tetravalent (ceric) salts, which are powerful but stable oxidizing agents, are used in analytical chemistry to determine oxidizable substances such as iron(II). Most cerium(IV) salts are orange to yellow in colour, as are solutions containing the Ce4+ ion. Cerium(III) behaves as a typical rare earth; its compounds are usually white.
Reference: Encyclopædia Britannica, Inc. 1994-2000 ©
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