BOILING POINT: 2,480°C
DENSITY: 8.253g/cm 3
MOST COMMON IONS: Tb 3+ , Tb 4+
In 1787, near Ytterby, Sweden, Swedish army officer Karl Axel Arrhenius discovered a mineral that he named ytterite. In 1794 Finnish chemist Johan Gadolin, working with ytterite, isolated a mixture of oxides (yttria) from which Carl G. Mosander in 1843 isolated three fractions: the oxide of the element yttrium (Y) and two other mixtures of oxides (old erbia and old terbia). In 1878 Swiss chemist Marc Delafontaine worked with "old erbia" but called it new new terbia. Also in 1878 J. C. Galissard de Marignac and Delafontaine, working with "new terbia," isolated an oxide of a new element, terbium. The element has an abundance of 0.91 × 10 −5 percent (by weight) in the igneous rocks of Earth's crust. Terbium's ground state electronic configuration is [Xe]4f 9 6s 2 . It has an atomic radius of 1.782 angstroms. Terbium has two crystallographic structures: α -Tb (room temperature to 1,310 ° C) and β -Tb (> 1,310 ° C). Bastnasite (fluorocarbonates), monazite, and xerotime (phosphates) are the principal terbium-containing minerals.
Terbium has two oxidation states: 3+, the most important, and 4+. Tb 4+ is a strong oxidizing agent. Tb 3+ salts are generally colorless or very pale pink. The Tb 3+ halides, except the fluoride compound, are soluble in water as well as in nitric acid, perchloric acid, and acetic acid. The hydroxide, oxide, phosphate, carbonate, and oxalate compounds are insoluble. A Tb 4+ oxide with a composition approaching Tb 4 O 7 (brown) is obtained via the calcination of several salts: carbonate, nitrate, and oxalate. The Tb 4+ compounds TbO 2 , with a fluorite-type lattice , and TbF 4 also exist.
Tb 3+ compounds and complexes in most cases exhibit strong luminescence in the green portion of visible light. Ternary compounds such as La 1− x − y Ce x Tb y PO 4 exhibit strong green emission radiation. Such kinds of compounds are called "phosphors" and are used to display color in television. Terbium is also used as an alloy material in compact discs.
Lea B. Zinner
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