Praseodymium

Carl Auer Von Welsbach
 * Praseodymium** is a chemical element that has the symbol **Pr** and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating. It is a soft and silver colored chemical element. The element was named for the color of its primary oxide. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare earth oxide residue he called "didymium" from a residue he called "lantana," in turn separated from cerium salts. In 1885, the Austrian chemist Baron Carl Auer von Welsbach separated didymium into two salts of different colors, which he named praseodymium and neodymium. The name praseodymium comes from the Greek //abrasions// (πράσιος), meaning green, and //didymos// (δίδυμος), twin. Like most rare earth elements, praseodymium most readily forms trivalent Pr(III) ions. These are yellow-green in water solution, and various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its use to filter yellow light from light sources.

Discovery of Praseodymium
Author: Dr. Doug Stewart Praseodymium was first identified in 1885 by Carl Auer von Welsbach. It was discovered in 'didymium' a substance incorrectly said by Carl Mosander to be a new element in 1841. (1) The nonexistent 'didymium' was even given the symbol Di in Mendeleev's first edition of the periodic table in 1869. In 1879 Lecoq de Boisbaudran detected and separated samarium from 'didymium.' (1a) After samarium had been discovered, it was noted that 'didymium's' absorption spectrum gave different results depending on which mineral it had been sourced from. (2) Bohuslav Brauner published a paper on atomic weight determinations in 1882 for rare earth elements and his data for 'didymium' were variable. Brauner became convinced that 'didymium' was a mixture of elements; he attempted to separate them, but he was not successful. (2) In 1885 Carl Welsbach, who had discovered 'didymium' 14 years earlier, realized it was actually a mixture of two entirely new elements. He named these praseodymium and neodymium. Welsbach reacted 'didymium' to form nitrate salts, which he then fractionally crystallized from nitric acid to yield greenish-brown praseodymium and pink neodymium salts. The fractional crystallization experiments were very time consuming, involving more than one hundred crystallization operations, each lasting up to 48 hours. Praseodymium was named using the Greek words 'prasios didymos' meaning 'green twin,' reflecting its green salts and the close association with neodymium. Pure metallic praseodymium was first produced in 1931. (3)


 * Uses**
 * used as a core material for carbon arc lights used by the motion picture industry
 * salts used to colour glasses and enamels; when mixed with certain other materials, praseodymium produces an intense clean yellow colour in glass. Component of didymium glass which is a colorant for welder's goggles
 * Misch metal, used in making cigarette lighters, contains about 5% praseodymium metal
 * alloys

Isotopes
Main article: [|Isotopes of praseodymium] Naturally occurring praseodymium is composed of one stable [|isotope], praseodymium-141, [|[5]] which is of use in [|NMR] and [|EPR spectroscopy]. [|[6]] 38 [|radioisotopes] have been characterized, with the most stable being praseodymium-143 with a [|half-life] of 13.57 days and praseodymium-142 with a half-life of 19.12 hours. [|[5]] All of the remaining [|radioactive] isotopes have half-lives that are less than six hours, and the majority of these have half lives that are less than 10 minutes. [|[5]] This element also has 15 [|nuclear isomers], with the longest-lived being praseodymium-138m, praseodymium-134m, and praseodymium-142m. [|[5]] The nuclei of nuclear isomers exist in a delicate equilibrium or [|metastability] due to at least one nucleon having an [|excited energy state]. The isotopes of praseodymium range in [|mass number] from 121 to 159. [|[5]] The most common [|decay mode] of 20 isotopes with mass numbers lower than the most abundant stable isotope, praseodymium-141 is [|beta+ decay], primarily forming cerium isotopes (58 protons) as [|decay products]. [|[5]] The most common decay mode for 18 isotopes with mass numbers higher than praseodymium-141 is [|beta- decay], primarily forming neodymium isotopes (60 protons) as decay products. [|[5]]