Praseodymium

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Praseodymium

Praseodymium is one of the rare earth elements found in Row 6 of the periodic table. The elements in this group are not especially rare, although they are quite difficult to separate from each other. Praseodymium has an atomic number of 59, an atomic mass of 140.9077, and a chemical symbol of Pr.

Properties

Praseodymium is a soft, malleable, ductile metal with a yellowish, metallic shine. It has a melting point of 1,710°F (930°C), a boiling point of about 5,800°F (about 3,200°C), and a density about 6.78-6.81 grams per cubic centimeter. Two allotropes of the element exist, accounting for the slight variation in densities.

Praseodymium is a moderately active element that reacts with oxygen in moist air to form a greenish yellow scale of praseodymium oxide (Pr₂O₃) that acts to protect the metal from further corrosion. Praseodymium also reacts with water and with acids with the production of hydrogen gas.

Occurrence and Extraction

Praseodymium is one of the more common rare earth elements with an abundance of about 3.5-5.5 parts per million in the Earth's crust. It occurs primarily with the other rare earth elements in two minerals, monazite and bastnasite. The element is extracted from its ores by converting the ore first to praseodymium fluoride (PrF₃) and then electrolyzing the fluoride: 2PrF₃ --electric current 2Pr + 3F₂.

Discovery and Naming

Praseodymium was one of seven new elements discovered in a mineral known as cerite first discovered in 1751 near the Swedish town of Bastnas. The discovery of praseodymium is credited to the Austrian chemist Carl Auer (Baron von Welsbach; 1858-1929) who found that a previously discovered element, didymium, was actually a mixture of two other new elements. Auer named the two new elements neodymium (for "new twin") and praseodymium (for "green twin"), the latter name because of the color of many of praseodymium's compounds.

Uses

One of the oldest uses for praseodymium is in the manufacture of misch metal, a pyrophoric metal (a metal that gives sparks when struck) used to make lighter flints and tracer bullets. Compounds of praseodymium are also used to give color to glass, ceramics, enamels, and other materials. The characteristic color provided by compounds of praseodymium in such cases is a bright yellow. Praseodymium is also added to the carbon in carbon arc lamps to produce a more brilliant white light.