praseodymium

Pr. Atomic number 59. A lanthanide element in group ³ of the periodic table with the electron configuration [Xe] ^4f36s2 . A member of the cerium group of rare earth elements. Atomic weight 140.90765(2). A mononuclear element with only one stable isotope, mass 141 (100%). Radioactive isotopes with mass numbers between 121 and 159 are known. In 1842, C.G. Mosander discovered a new element in the mineral in which he had found lanthanum, with properties very similar to lanthanum, and named it Dydimium, from the Greek word διδυμο (didymos), meaning twin. In 1885, CF Auer von Welsbach of Austria further separated didymium into two elements, one of which he named the "new twin" Neodymium, and the other of which he named Praseodimium, the "green twin" after the Greek word πρασιο (prasios), meaning green, because it gives green salt. The Japanese name for the element is a transliteration of the German name Praseodym.
It is found in monazite and bastnaesite. Its abundance in the earth's crust is 3.9 ppm. China ranks first in both rare earth reserves (30%) and production (98%) in 2007. After rare earth separation by solvent extraction, the metal obtained by electrolysis of a mixture of molten chlorides and fluorides with alkali metal chlorides and fluorides is silvery white. There are two types of metal: the α form with a hexagonal close-packed structure, and the β form with a body-centered cubic structure above 792 °C. Its melting point is 931 °C, and its boiling point is 3512 °C. The densities are α form: 6.773 g cm ^-3 , β form: 6.64 g cm ^-3 . Hardness is 6.5. It is easily soluble in acid and hot water, and generates H _2. First ionization energy is 5.464 eV. Oxidation states are 3 and 4. As with other rare earths, trivalent compounds such as carbonates, oxalates, and fluorides are insoluble in water. The salts, both as crystals and in aqueous solution, are green. The electron configurations of _Pr3 ⁺ and Pr4 ⁺ are ^4f2 and ^4f1 , making _them paramagnetic. ^PrⅣ compounds are very rare, and the black oxide obtained when ^PrⅢ2O3 is heated in air is called ^PrⅣO2 _, but is close to being a non-stoichiometric compound.
The standard electrode potential of Pr4 ⁺ /Pr3 ⁺ is 2.86 V, making _it a strong oxidizing agent that decomposes water to generate oxygen. In addition, _Na2PrIVF6 can be obtained ^by heating Pr salts to 300-500°C in an _F2 atmosphere. It is one of the components of ignition alloys for lighters. The oxide is a component of carbon electrodes for arc lamps. The salt is used to color glass. Alloys with magnesium are used in jet engine parts due to their high tensile and low creep properties. [CAS 7440-10-0]

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

Pr．原子番号59の元素．電子配置[Xe]4f ³6s²の周期表3族ランタノイド元素．希土類元素セリウム族の一つ．原子量140.90765(2)．安定同位体が質量数141(100％)のみの単核種元素．質量数121～159の放射性同位体が知られている．1842年，C.G. Mosanderはランタンを発見した鉱物中に，さらにランタンと性質がよく似た新元素を発見し，ギリシア語の双子を意味するδιδυμο(didymos)からDydimium(ジジム)と命名した．1885年に至り，オーストリアのC.F. Auer von Welsbach(ウェルスバッハ)がジジムをさらに二元素に分離し，一方を“新しい双子”Neodymium(ネオジム)，他方を緑色の塩を与えることから，ギリシア語の緑を意味するπρασιο(prasios)と合わせて“緑の双子”Praseodimiumと命名した．日本語の元素名はドイツ語の元素名Praseodymの音訳．
モナズ石，バストネス石に含まれる．地殻中の存在度3.9 ppm．中国では全希土類の埋蔵量(30％)・生産量(98％)でともに一位(2007年)．溶媒抽出法で希土類相互分離後，塩化物・フッ化物のアルカリ金属塩化物・フッ化物との混合溶融塩電解により得られる金属は銀白色．六方最密構造のα態と，792 ℃ 以上の体心立方構造のβ態がある．融点931 ℃，沸点3512 ℃．密度はα態：6.773 g cm^－3，β態：6.64 g cm^－3．硬さ6.5．酸と熱水に易溶で，H₂ を発生する．第一イオン化エネルギー5.464 eV．酸化数3，4．三価の化合物はほかの希土類と同じく，炭酸塩，シュウ酸塩，フッ化物などが水に不溶．塩類は結晶，水溶液ともに緑色．Pr^3＋，Pr^4＋ の電子配置は4f ²，4f ¹で常磁性．Pr^Ⅳ化合物は非常に少なく，Pr^Ⅲ₂O₃を空気中で加熱すると得られる黒色の酸化物はPr^Ⅳ O₂と表されるが不定比化合物に近い．
Pr^4＋/Pr^3＋ の標準電極電位は2.86 V と強力な酸化剤で，水を分解して酸素を発生させる．このほか，Na₂Pr^Ⅳ F₆はPr塩を F₂ 雰囲気中で300～500 ℃ に加熱すると得られる．ライター用発火合金の成分の一つ．酸化物はアーク灯炭素電極の成分．塩はガラスの着色に使われる．マグネシウムとの合金は，高張力・低クリープ特性でジェットエンジン部品に使用される．[CAS 7440-10-0]

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