Praseodymium

Praseodymium is a chemical element with symbol Pr and atomic number 59. It is the third member of the lanthanide series and is traditionally considered to be one of the rare-earth metals. Praseodymium is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.

Praseodymium always occurs naturally together with the other rare-earth metals. It is the fourth most common rare-earth element, making up 9.1 parts per million of the Earth's crust, an abundance similar to that of boron. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare-earth oxide residue he called didymium from a residue he called "lanthana", in turn separated from cerium salts. In 1885, the Austrian chemist Baron Carl Auer von Welsbach separated didymium into two elements that gave salts of different colours, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasinos (πράσινος), meaning "green", and didymos (δίδυμος), "twin".

Like most rare-earth elements, praseodymium most readily forms the +3 oxidation state, which is the only stable state in aqueous solution, although the +4 oxidation state is known in some solid compounds and, uniquely among the lanthanides, the +5 oxidation state is attainable in matrix-isolation conditions. Aqueous praseodymium ions are yellowish-green, and similarly praseodymium results in various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its ability to filter yellow light from light sources.

Praseodymium,  59Pr
Praseodymium
Pronunciation	/ˌpreɪziːəˈdɪmiəm/[1] ​(PRAY-zee-ə-DIM-ee-əm)
Appearance	grayish white
Standard atomic weight Ar, std(Pr)	140.90766(1)[2]
Praseodymium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ Pr ↓ Pa cerium ← praseodymium → neodymium
Atomic number (Z)	59
Group	group n/a
Period	period 6
Block	f-block
Element category	lanthanide
Electron configuration	[Xe] 4f3 6s2
Electrons per shell	2, 8, 18, 21, 8, 2
Physical properties
Phase at STP	solid
Melting point	1208 K ​(935 °C, ​1715 °F)
Boiling point	3403 K ​(3130 °C, ​5666 °F)
Density (near r.t.)	6.77 g/cm3
when liquid (at m.p.)	6.50 g/cm3
Heat of fusion	6.89 kJ/mol
Heat of vaporization	331 kJ/mol
Molar heat capacity	27.20 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1771 1973 (2227) (2571) (3054) (3779)
Atomic properties
Oxidation states	+1,[3] +2, +3, +4, +5 (a mildly basic oxide)
Electronegativity	Pauling scale: 1.13
Ionization energies	1st: 527 kJ/mol 2nd: 1020 kJ/mol 3rd: 2086 kJ/mol
Atomic radius	empirical: 182 pm
Covalent radius	203±7 pm
Spectral lines of praseodymium
Other properties
Natural occurrence	primordial
Crystal structure	​double hexagonal close-packed (dhcp)
Speed of sound thin rod	2280 m/s (at 20 °C)
Thermal expansion	α, poly: 6.7 µm/(m·K) (at r.t.)
Thermal conductivity	12.5 W/(m·K)
Electrical resistivity	α, poly: 0.700 µΩ·m (at r.t.)
Magnetic ordering	paramagnetic[4]
Magnetic susceptibility	+5010.0·10−6 cm3/mol (293 K)[5]
Young's modulus	α form: 37.3 GPa
Shear modulus	α form: 14.8 GPa
Bulk modulus	α form: 28.8 GPa
Poisson ratio	α form: 0.281
Vickers hardness	250–745 MPa
Brinell hardness	250–640 MPa
CAS Number	7440-10-0
History
Discovery	Carl Auer von Welsbach (1885)
Main isotopes of praseodymium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 141Pr 100% stable 142Pr syn 19.12 h β− 142Nd ε 142Ce 143Pr syn 13.57 d β− 143Nd

Characteristics

Physical

Praseodymium is the third member of the lanthanide series. In the periodic table, it appears between the lanthanides cerium to its left and neodymium to its right, and above the actinide protactinium. It is a ductile metal with a hardness comparable to that of silver.^[6] Its 59 electrons are arranged in the configuration [Xe]4f³6s²; theoretically, all five outer electrons can act as valence electrons, but the use of all five requires extreme conditions and normally, praseodymium only gives up three or sometimes four electrons in its compounds. Praseodymium is the first of the lanthanides to have an electron configuration conforming to the Aufbau principle, which predicts the 4f orbitals to have a lower energy level than the 5d orbitals; this does not hold for lanthanum and cerium, because the sudden contraction of the 4f orbitals does not happen until after lanthanum, and is not strong enough at cerium to avoid occupying the 5d subshell. Nevertheless, solid praseodymium takes on the [Xe]4f²5d¹6s² configuration, with one electron in the 5d subshell like all the other trivalent lanthanides (all but europium and ytterbium, which are divalent in the metallic state).^[7]

Like most lanthanides, praseodymium usually only uses three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: this is because the 4f orbitals penetrate the most through the inert xenon core of electrons to the nucleus, followed by 5d and 6s, and this increases with higher ionic charge. Praseodymium nevertheless can continue losing a fourth and even occasionally a fifth valence electron because it comes very early in the lanthanide series, where the nuclear charge is still low enough and the 4f subshell energy high enough to allow the removal of further valence electrons.^[8] Thus, similarly to the other early trivalent lanthanides, praseodymium has a double hexagonal close-packed crystal structure at room temperature. At about 560 °C, it transitions to a face-centered cubic structure, and a body-centered cubic structure appears shortly before the melting point of 935 °C.^[9]

Praseodymium, like all of the lanthanides (except lanthanum, ytterbium, and lutetium, which have no unpaired 4f electrons), is paramagnetic at room temperature.^[10] Unlike some other rare-earth metals, which show antiferromagnetic or ferromagnetic ordering at low temperatures, praseodymium is paramagnetic at all temperatures above 1 K.^[4]

Isotopes

Praseodymium has only one stable and naturally occurring isotope, ¹⁴¹Pr. It is thus a mononuclidic element, and its standard atomic weight can be determined with high precision as it is a constant of nature. This isotope has 82 neutrons, a magic number that confers additional stability.^[11] This isotope is produced in stars through the s- and r-processes (slow and rapid neutron capture, respectively).^[12]

All other praseodymium isotopes have half-lives under a day (and most under a minute), with the single exception of ¹⁴³Pr with a half-life of 13.6 days. Both ¹⁴³Pr and ¹⁴¹Pr occur as fission products of uranium. The primary decay mode of isotopes lighter than ¹⁴¹Pr is inverse beta decay or electron capture to isotopes of cerium, while that of heavier isotopes is beta decay to isotopes of neodymium.^[11]

Chemistry

Praseodymium metal tarnishes slowly in air, forming a spalling oxide layer like iron rust; a centimetre-sized sample of praseodymium metal corrodes completely in about a year.^[13] It burns readily at 150 °C to form praseodymium (III,IV) oxide, a nonstoichiometric compound approximating to Pr₆O₁₁:^[14]

12 Pr + 11 O₂ → 2 Pr₆O₁₁

This may be reduced to praseodymium(III) oxide (Pr₂O₃) with hydrogen gas.^[15] The dark-coloured praseodymium(IV) oxide, PrO₂, is the most oxidised product of the combustion of praseodymium and is only obtained by reaction of praseodymium metal with pure oxygen at 400 °C and 282 bar.^[15] The reactivity of praseodymium conforms to periodic trends, as it is one of the first and thus one of the largest lanthanides.^[8] At 1000 °C, many praseodymium oxides with composition PrO_2−x exist as disordered, nonstoichiometric phases with 0 < x < 0.25, but at 400–700 °C the oxide defects are instead ordered, creating phases of the general formula Pr_nO_2n−2 with n = 4, 7, 9, 10, 11, 12, and ∞. These phases PrO_y are sometimes labelled α and β′ (nonstoichiometric), β (y = 1.833), δ (1.818), ε (1.8), ζ (1.778), ι (1.714), θ, and σ.^[16]

Praseodymium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form praseodymium(III) hydroxide:^[14]

2 Pr (s) + 6 H₂O (l) → 2 Pr(OH)₃ (aq) + 3 H₂ (g)

Praseodymium metal reacts with all the halogens to form trihalides:^[14]

2 Pr (s) + 3 F₂ (g) → 2 PrF₃ (s) [green]

2 Pr (s) + 3 Cl₂ (g) → 2 PrCl₃ (s) [green]

2 Pr (s) + 3 Br₂ (g) → 2 PrBr₃ (s) [green]

2 Pr (s) + 3 I₂ (g) → 2 PrI₃ (s)

The tetrafluoride, PrF₄, is also known, and is produced by reacting a mixture of sodium fluoride and praseodymium(III) fluoride with fluorine gas, producing Na₂PrF₆, following which sodium fluoride is removed from the reaction mixture with liquid hydrogen fluoride.^[17] Additionally, praseodymium forms a bronze diiodide; like the diiodides of lanthanum, cerium, and gadolinium, it is a praseodymium(III) electride compound.^[17]

Praseodymium dissolves readily in dilute sulfuric acid to form solutions containing the chartreuse Pr³⁺ ions, which exist as [Pr(H₂O)₉]³⁺ complexes:^[14][18]

2 Pr (s) + 3 H₂SO₄ (aq) → 2 Pr³⁺ (aq) + 3 SO²⁻
₄ (aq) + 3 H₂ (g)

Dissolving praseodymium(IV) compounds in water results in solutions containing the yellow Pr⁴⁺ ions;^[19] because of the high positive standard reduction potential of the Pr⁴⁺/Pr³⁺ couple at +3.2 V, these ions are unstable in aqueous solution, oxidising water and being reduced to Pr³⁺. The value for the Pr³⁺/Pr couple is −2.35 V.^[7]

Although praseodymium(V) in the bulk state is unknown, the existence of praseodymium in its +5 oxidation state (with the stable electron configuration of the preceding noble gas xenon) under noble-gas matrix isolation conditions was reported in 2016. The species assigned to the +5 state were identified as [PrO₂]⁺, its O₂ and Ar adducts, and PrO₂(η²-O₂).^[20]

Organopraseodymium compounds are very similar to those of the other lanthanides, as they all share an inability to undergo π backbonding. They are thus mostly restricted to the mostly ionic cyclopentadienides (isostructural with those of lanthanum) and the σ-bonded simple alkyls and aryls, some of which may be polymeric.^[21] The coordination chemistry of praseodymium is largely that of the large, electropositive Pr³⁺ ion, and is thus largely similar to those of the other early lanthanides La³⁺, Ce³⁺, and Nd³⁺. For instance, like lanthanum, cerium, and neodymium, praseodymium nitrates form both 4:3 and 1:1 complexes with 18-crown-6, whereas the middle lanthanides from promethium to gadolinium can only form the 4:3 complex and the later lanthanides from terbium to lutetium cannot successfully coordinate to all the ligands. Such praseodymium complexes have high but uncertain coordination numbers and poorly defined stereochemistry, with exceptions resulting from exceptionally bulky ligands such as the tricoordinate [Pr{N(SiMe₃)₂}₃]. There are also a few mixed oxides and fluorides involving praseodymium(IV), but it does not have an appreciable coordination chemistry in this oxidation state like its neighbour cerium.^[22]

History

In 1751, the Swedish mineralogist Axel Fredrik Cronstedt discovered a heavy mineral from the mine at Bastnäs, later named cerite. Thirty years later, the fifteen-year-old Vilhelm Hisinger, from the family owning the mine, sent a sample of it to Carl Scheele, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with Jöns Jacob Berzelius and isolated a new oxide, which they named ceria after the dwarf planet Ceres, which had been discovered two years earlier.^[23] Ceria was simultaneously and independently isolated in Germany by Martin Heinrich Klaproth.^[24] Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist Carl Gustaf Mosander, who lived in the same house as Berzelius; he separated out two other oxides, which he named lanthana and didymia.^[25] He partially decomposed a sample of cerium nitrate by roasting it in air and then treating the resulting oxide with dilute nitric acid. The metals that formed these oxides were thus named lanthanum and didymium.^[26] While lanthanum turned out to be a pure element, didymium was not and turned out to be only a mixture of all the stable early lanthanides from praseodymium to europium, as had been suspected by Marc Delafontaine after spectroscopic analysis, though he lacked the time to pursue its separation into its constituents. The heavy pair of samarium and europium were only removed in 1879 by Paul-Émile Lecoq de Boisbaudran and it was not until 1885 that Carl Auer von Welsbach separated didymium into praseodymium and neodymium.^[27] Since neodymium was a larger constituent of didymium than praseodymium, it kept the old name with disambiguation, while praseodymium was distinguished by the leek-green colour of its salts (Greek πρασιος, "leek green").^[28] The composite nature of didymium had previously been suggested in 1882 by Bohuslav Brauner, who did not experimentally pursue its separation.^[29]

Occurrence and production

Praseodymium is not particularly rare, making up 9.1 mg/kg of the Earth's crust. This value is between those of lead (13 mg/kg) and boron (9 mg/kg), and makes praseodymium the fourth-most abundant of the lanthanides, behind cerium (66 mg/kg), neodymium (40 mg/kg), and lanthanum (35 mg/kg); it is less abundant than the rare-earth elements yttrium (31 mg/kg) and scandium (25 mg/kg).^[28] Instead, praseodymium's classification as a rare-earth metal comes from its rarity relative to "common earths" such as lime and magnesia, the few known minerals containing it for which extraction is commercially viable, as well as the length and complexity of extraction.^[30] Although not particularly rare, praseodymium is never found as a dominant rare earth in praseodymium-bearing minerals. It is always preceded by cerium, lanthanum and usually also by neodymium.^[31]

The Pr³⁺ ion is similar in size to the early lanthanides of the cerium group (those from lanthanum up to samarium and europium) that immediately follow in the periodic table, and hence it tends to occur along with them in phosphate, silicate and carbonate minerals, such as monazite (M^IIIPO₄) and bastnäsite (M^IIICO₃F), where M refers to all the rare-earth metals except scandium and the radioactive promethium (mostly Ce, La, and Y, with somewhat less Nd and Pr).^[28] Bastnäsite is usually lacking in thorium and the heavy lanthanides, and the purification of the light lanthanides from it is less involved. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, evolving carbon dioxide, hydrogen fluoride, and silicon tetrafluoride. The product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.^[28]

The procedure for monazite, which usually contains all the rare earths, as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralised with sodium hydroxide to pH 3–4, during which thorium precipitates as a hydroxide and is removed. The solution is treated with ammonium oxalate to convert rare earths to their insoluble oxalates, the oxalates are converted to oxides by annealing, and the oxides are dissolved in nitric acid. This last step excludes one of the main components, cerium, whose oxide is insoluble in HNO₃.^[30] Care must be taken when handling some of the residues as they contain ²²⁸Ra, the daughter of ²³²Th, which is a strong gamma emitter.^[28]

Praseodymium may then be separated from the other lanthanides via ion-exchange chromatography, or by using a solvent such as tributyl phosphate where the solubility of Ln³⁺ increases as the atomic number increases. If ion-exchange chromatography is used, the mixture of lanthanides is loaded into one column of cation-exchange resin and Cu²⁺ or Zn²⁺ or Fe³⁺ is loaded into the other. An aqueous solution of a complexing agent, known as the eluant (usually triammonium edtate), is passed through the columns, and Ln³⁺ is displaced from the first column and redeposited in a compact band at the top of the column before being re-displaced by NH⁺
₄. The Gibbs free energy of formation for Ln(edta·H) complexes increases along the lanthanides by about one quarter from Ce³⁺ to Lu³⁺, so that the Ln³⁺ cations descend the development column in a band and are fractionated repeatedly, eluting from heaviest to lightest. They are then precipitated as their insoluble oxalates, burned to form the oxides, and then reduced to the metals.^[28]

Applications

Leo Moser (son of Ludwig Moser, founder of the Moser Glassworks in what is now Karlovy Vary in the Czech Republic, not to be confused with the mathematician of the same name) investigated the use of praseodymium in glass colouration in the late 1920s, yielding a yellow-green glass given the name "Prasemit". However, at that time far cheaper colourants could give a similar colour, so Prasemit was not popular, few pieces were made, and examples are now extremely rare. Moser also blended praseodymium with neodymium to produce "Heliolite" glass ("Heliolit" in German), which was more widely accepted. The first enduring commercial use of purified praseodymium, which continues today, is in the form of a yellow-orange "Praseodymium Yellow" stain for ceramics, which is a solid solution in the zircon lattice. This stain has no hint of green in it; by contrast, at sufficiently high loadings, praseodymium glass is distinctly green rather than pure yellow.^[32]

As the lanthanides are so similar, praseodymium can substitute for most other lanthanides without significant loss of function, and indeed many applications such as mischmetal and ferrocerium alloys involve variable mixes of several lanthanides, including small quantities of praseodymium. The following more modern applications involve praseodymium specifically, or at least praseodymium in a small subset of the lanthanides:^[33]

• In combination with neodymium, another rare-earth element, praseodymium is used to create high-power magnets notable for their strength and durability.^[34] In general, most alloys of the cerium-group rare earths (lanthanum through samarium) with 3d transition metals give extremely stable magnets that are often used in small equipment, such as motors, printers, watches, headphones, loudspeakers, and magnetic storage.^[33]
• As an alloying agent with magnesium to create high-strength metals that are used in aircraft engines; yttrium and neodymium are also viable substitutes.^[35][36]
• Praseodymium is present in the rare-earth mixture whose fluoride forms the core of carbon arc lights, which are used in the motion picture industry for studio lighting and projector lights.^[37]
• Praseodymium compounds give glasses and enamels a yellow color.^[6]
• Praseodymium is used to color ceramics yellow.^[33]
• Praseodymium is a component of didymium glass, which is used to make certain types of welder's and glass blower's goggles.^[6]
• Silicate crystals doped with praseodymium ions have been used to slow a light pulse down to a few hundred meters per second.^[38]
• Praseodymium alloyed with nickel (PrNi₅) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero.^[37]
• Doping praseodymium in fluoride glass allows it to be used as a single-mode fiber optical amplifier.^[39]
• Praseodymium oxide in solid solution with ceria or ceria-zirconia has been used as an oxidation catalyst.^[40]
• Pr³⁺ ions are used as activators in some red, green, blue, and ultraviolet phosphors.^[33]

Biological role and precautions

Praseodymium
Hazards
GHS pictograms
GHS signal word	Danger
GHS hazard statements	H250
GHS precautionary statements	P222, P231, P422[41]
NFPA 704	4 0 4

The early lanthanides have been found to be essential to some methanotrophic bacteria living in volcanic mudpots, such as Methylacidiphilum fumariolicum: lanthanum, cerium, praseodymium, and neodymium are about equally effective.^[42] Praseodymium is otherwise not known to have a biological role in any other organisms, but is not very toxic either. Intravenous injection of rare earths into animals has been known to impair liver function, but the main side effects from inhalation of rare-earth oxides in humans come from radioactive thorium and uranium impurities.^[33]

References

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2. ^ Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
3. ^ Chen, Xin; et al. (2019-12-13). "Lanthanides with Unusually Low Oxidation States in the PrB^3– and PrB^4– Boride Clusters". Retrieved 2019-02-13.
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5. ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
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7. ^ ^{a b} Greenwood and Earnshaw, pp. 1232–5
8. ^ ^{a b} Greenwood and Earnshaw, pp. 1235–8
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10. ^ Cullity, B. D.; Graham, C. D. (2011). Introduction to Magnetic Materials. John Wiley & Sons. ISBN 978-1-118-21149-6.
11. ^ ^{a b} Audi, Georges; Bersillon, O.; Blachot, J.; Wapstra, A.H. (2003). "The NUBASE Evaluation of Nuclear and Decay Properties". Nuclear Physics A. 729 (1): 3–128. Bibcode:2003NuPhA.729....3A. CiteSeerX 10.1.1.692.8504. doi:10.1016/j.nuclphysa.2003.11.001.
12. ^ Cameron, A. G. W. (1973). "Abundance of the Elements in the Solar System" (PDF). Space Science Reviews. 15 (1): 121–146. Bibcode:1973SSRv...15..121C. doi:10.1007/BF00172440. Archived from the original (PDF) on 2011-10-21.
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25. ^ Weeks, Mary Elvira (1932). "The Discovery of the Elements: XI. Some Elements Isolated with the Aid of Potassium and Sodium:Zirconium, Titanium, Cerium and Thorium". The Journal of Chemical Education. 9 (7): 1231–1243. Bibcode:1932JChEd...9.1231W. doi:10.1021/ed009p1231.
26. ^ See:
    • (Berzelius) (1839) "Nouveau métal" (New metal), Comptes rendus, 8 : 356–357. From p. 356: "L'oxide de cérium, extrait de la cérite par la procédé ordinaire, contient à peu près les deux cinquièmes de son poids de l'oxide du nouveau métal qui ne change que peu les propriétés du cérium, et qui s'y tient pour ainsi dire caché. Cette raison a engagé M. Mosander à donner au nouveau métal le nom de Lantane." (The oxide of cerium, extracted from cerite by the usual procedure, contains almost two fifths of its weight in the oxide of the new metal, which differs only slightly from the properties of cerium, and which is held in it so to speak "hidden". This reason motivated Mr. Mosander to give to the new metal the name Lantane.)
    • (Berzelius) (1839) "Latanium — a new metal," Philosophical Magazine, new series, 14 : 390–391.
27. ^ Fontani, Marco; Costa, Mariagrazia; Orna, Virginia (2014). The Lost Elements: The Periodic Table's Shadow Side. Oxford University Press. pp. 122–123. ISBN 978-0-19-938334-4.
28. ^ ^{a b c d e f} Greenwood and Earnshaw, p. 1229–32
29. ^ Fontani, Marco; Costa, Mariagrazia; Orna, Virginia (2014). The Lost Elements: The Periodic Table's Shadow Side. Oxford University Press. p. 40. ISBN 978-0-19-938334-4.
30. ^ ^{a b} Patnaik, Pradyot (2003). Handbook of Inorganic Chemical Compounds. McGraw-Hill. pp. 444–446. ISBN 978-0-07-049439-8. Retrieved 2009-06-06.
31. ^ Hudson Institute of Mineralogy (1993–2018). "Mindat.org". www.mindat.org. Retrieved 14 January 2018.
32. ^ Kreidl, Norbert J. (1942). "RARE EARTHS*". Journal of the American Ceramic Society. 25 (5): 141–143. doi:10.1111/j.1151-2916.1942.tb14363.x.
33. ^ ^{a b c d e} McGill, Ian, "Rare Earth Elements", Ullmann's Encyclopedia of Industrial Chemistry, 31, Weinheim: Wiley-VCH, p. 183–227, doi:10.1002/14356007.a22_607
34. ^ Rare Earth Elements 101 Archived 2013-11-22 at the Wayback Machine, IAMGOLD Corporation, April 2012, pp. 5, 7.
35. ^ Rokhlin, L. L. (2003). Magnesium alloys containing rare earth metals: structure and properties. CRC Press. ISBN 978-0-415-28414-1.
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37. ^ ^{a b} Emsley, pp. 423–5
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Bibliography

• Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements. Oxford University Press. ISBN 978-0-19-960563-7.
• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9.

Further reading

• R. J. Callow, The Industrial Chemistry of the Lanthanons, Yttrium, Thorium and Uranium, Pergamon Press, 1967.

External links

• WebElements.com—Praseodymium
• It's Elemental—The Element Praseodymium

Ap and Bp stars

Ap and Bp stars are chemically peculiar stars (hence the "p") of types A and B which show overabundances of some metals, such as strontium, chromium and europium. In addition, larger overabundances are often seen in praseodymium and neodymium. These stars have a much slower rotation than normal for A and B-type stars, although some exhibit rotation velocities up to about 100 kilometers per second.

Cerium

Cerium is a chemical element with symbol Ce and atomic number 58. Cerium is a soft, ductile and silvery-white metal that tarnishes when exposed to air, and it is soft enough to be cut with a knife. Cerium is the second element in the lanthanide series, and while it often shows the +3 oxidation state characteristic of the series, it also exceptionally has a stable +4 state that does not oxidize water. It is also considered one of the rare-earth elements. Cerium has no biological role and is not very toxic.

Despite always occurring in combination with the other rare-earth elements in minerals such as those of the monazite and bastnäsite groups, cerium is easy to extract from its ores, as it can be distinguished among the lanthanides by its unique ability to be oxidized to the +4 state. It is the most common of the lanthanides, followed by neodymium, lanthanum, and praseodymium. It is the 26th-most abundant element, making up 66 ppm of the Earth's crust, half as much as chlorine and five times as much as lead.

Cerium was the first of the lanthanides to be discovered, in Bastnäs, Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger in 1803, and independently by Martin Heinrich Klaproth in Germany in the same year. In 1839 Carl Gustaf Mosander became the first to isolate the metal. Today, cerium and its compounds have a variety of uses: for example, cerium(IV) oxide is used to polish glass and is an important part of catalytic converters. Cerium metal is used in ferrocerium lighters for its pyrophoric properties. Cerium-doped YAG phosphor is used in blue light-emitting diodes to produce white light.

Didymium

For the amoeboid genus see Didymium (genus).Didymium (Greek: twin element) is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially when a gas (propane)-powered forge is used, where it provides a filter that selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass, without having a detrimental effect on general vision, unlike dark welder's glasses. The strong infrared light emitted by the superheated forge gases and insulation lining the forge walls is also blocked thereby saving the crafters' eyes from serious cumulative damage such as glassblower's cataract. The usefulness of didymium glass for eye protection of this sort was discovered by Sir William Crookes.

Didymium photographic filters are often used to enhance autumn scenery by making leaves appear more vibrant. It does this by removing part of the orange region of the color spectrum, acting as an optical band-stop filter. Unfiltered, this group of colors tends to make certain elements of a picture appear "muddy". These photographic filters are also used by nightscape photographers as they absorb part of the light pollution caused by sodium street lights. Didymium was also used in the sodium vapor process for matte work due to its ability to absorb the yellow color produced by its eponymous sodium lighting.

Didymium is also used in calibration materials for spectroscopy.

Isotopes of neodymium

Naturally occurring neodymium (60Nd) is composed of 5 stable isotopes, 142Nd, 143Nd, 145Nd, 146Nd and 148Nd, with 142Nd being the most abundant (27.2% natural abundance), and 2 long-lived radioisotopes, 144Nd and 150Nd. In all, 33 radioisotopes of neodymium have been characterized up to now, with the most stable being naturally occurring isotopes 144Nd (alpha decay, a half-life (t1/2) of 2.29×1015 years) and 150Nd (double beta decay, t1/2 of 7×1018 years). All of the remaining radioactive isotopes have half-lives that are less than 12 days, and the majority of these have half-lives that are less than 70 seconds; the most stable artificial isotope is 147Nd with a half-life of 10.98 days. This element also has 13 known meta states with the most stable being 139mNd (t1/2 5.5 hours), 135mNd (t1/2 5.5 minutes) and 133m1Nd (t1/2 ~70 seconds).

The primary decay modes before the most abundant stable isotope, 142Nd, are electron capture and positron decay, and the primary mode after is beta decay. The primary decay products before 142Nd are element Pr (praseodymium) isotopes and the primary products after are element Pm (promethium) isotopes.

Isotopes of praseodymium

Naturally occurring praseodymium (59Pr) is composed of one stable isotope, 141Pr. Thirty-eight radioisotopes have been characterized with the most stable being 143Pr, with a half-life of 13.57 days and 142Pr, with a half-life of 19.12 hours. All of the remaining radioactive isotopes have half-lives that are less than 5.985 hours and the majority of these have half-lives that are less than 33 seconds. This element also has 15 meta states with the most stable being 138mPr (t1/2 2.12 hours), 142mPr (t1/2 14.6 minutes) and 134mPr (t1/2 11 minutes).

The isotopes of praseodymium range in atomic weight from 120.955 u (121Pr) to 158.955 u (159Pr). The primary decay mode before the stable isotope, 141Pr, is electron capture and the mode after is beta decay. The primary decay products before 141Pr are element 58 (cerium) isotopes and the primary products after are element 60 (neodymium) isotopes.

Kondo effect

In physics, the Kondo effect describes the scattering of conduction electrons in a metal due to magnetic impurities, resulting in a characteristic change in electrical resistivity with temperature.

The effect was first described by Jun Kondo, who applied third-order perturbation theory to the problem to account for s-d electron scattering. Kondo's model predicted that the scattering rate of conduction electrons of the magnetic impurity should diverge as the temperature approaches 0 K. Extended to a lattice of magnetic impurities, the Kondo effect likely explains the formation of heavy fermions and Kondo insulators in intermetallic compounds, especially those involving rare earth elements like cerium, praseodymium, and ytterbium, and actinide elements like uranium. The Kondo effect has also been observed in quantum dot systems.

Major actinide

Major actinides is a term used in the nuclear power industry that refers to the plutonium and uranium present in used nuclear fuel, as opposed to the minor actinides neptunium, americium, curium, berkelium, and californium.

Neodymium

Neodymium is a chemical element with symbol Nd and atomic number 60. It is a soft silvery metal that tarnishes in air. Neodymium was discovered in 1885 by the Austrian chemist Carl Auer von Welsbach. It is present in significant quantities in the ore minerals monazite and bastnäsite. Neodymium is not found naturally in metallic form or unmixed with other lanthanides, and it is usually refined for general use. Although neodymium is classed as a rare earth, it is a fairly common element, no rarer than cobalt, nickel, or copper, and is widely distributed in the Earth's crust. Most of the world's commercial neodymium is mined in China.

Neodymium compounds were first commercially used as glass dyes in 1927, and they remain a popular additive in glasses. The color of neodymium compounds—due to the Nd3+ ion—is often a reddish-purple but it changes with the type of lighting, due to the interaction of the sharp light absorption bands of neodymium with ambient light enriched with the sharp visible emission bands of mercury, trivalent europium or terbium. Some neodymium-doped glasses are also used in lasers that emit infrared with wavelengths between 1047 and 1062 nanometers. These have been used in extremely-high-power applications, such as experiments in inertial confinement fusion.

Neodymium is also used with various other substrate crystals, such as yttrium aluminium garnet in the Nd:YAG laser. This laser usually emits infrared at a wavelength of about 1064 nanometers. The Nd:YAG laser is one of the most commonly used solid-state lasers.

Another important use of neodymium is as a component in the alloys used to make high-strength neodymium magnets—powerful permanent magnets. These magnets are widely used in such products as microphones, professional loudspeakers, in-ear headphones, high performance hobby DC electric motors, and computer hard disks, where low magnet mass (or volume) or strong magnetic fields are required. Larger neodymium magnets are used in high-power-versus-weight electric motors (for example in hybrid cars) and generators (for example aircraft and wind turbine electric generators).

Neutron number

The neutron number, symbol N, is the number of neutrons in a nuclide.

Atomic number (proton number) plus neutron number equals mass number: Z+N=A. The difference between the neutron number and the atomic number is known as the neutron excess: D = N - Z = A - 2Z.

Neutron number is rarely written explicitly in nuclide symbol notation, but appears as a subscript to the right of the element symbol. In order of increasing explicitness and decreasing frequency of usage:

Nuclides that have the same neutron number but a different proton number are called isotones. This word was formed by replacing the p in isotope with n for neutron. Nuclides that have the same mass number are called isobars. Nuclides that have the same neutron excess are called isodiaphers.Chemical properties are primarily determined by proton number, which determines which chemical element the nuclide is a member of; neutron number has only a slight influence.

Neutron number is primarily of interest for nuclear properties. For example, actinides with odd neutron number are usually fissile (fissionable with slow neutrons) while actinides with even neutron number are usually not fissile (but are fissionable with fast neutrons).

Only 57 stable nuclides have an odd neutron number, compared to 200 with an even neutron number. No odd-neutron-number isotope is the most naturally abundant isotope in its element, except for beryllium-9 which is the only stable beryllium isotope, nitrogen-14, and platinum-195.

No stable nuclides have neutron number 19, 21, 35, 39, 45, 61, 89, 115, 123, and ≥ 127. There are 6 stable nuclides and one radioactive primordial nuclide with neutron number 82 (82 is the neutron number with the most stable nuclides, since it is a magic number): barium-138, lanthanum-139, cerium-140, praseodymium-141, neodymium-142, and samarium-144, as well as the radioactive primordial nuclide xenon-136. Except 20, 50 and 82 (all these three numbers are magic numbers), all other neutron numbers have at most 4 stable isotopes (in the case of 20, there are 5 stable isotopes 36S, 37Cl, 38Ar, 39K, and 40Ca, and in the case for 50, there are 5 stable nuclides: 86Kr, 88Sr, 89Y, 90Zr, and 92Mo, and 1 radioactive primordial nuclide, 87Rb). All odd neutron numbers have at most one stable isotope (except 1 (2H and 3He), 5 (9Be and 10B), 7 (13C and 14N), 55 (97Mo and 99Ru) and 107 (179Hf and 180mTa). However, some even neutron numbers also have only one stable isotope; these numbers are 2 (4He), 4 (7Li), 84 (142Ce), 86 (146Nd) and 126 (208Pb).

Only two stable nuclides have fewer neutrons than protons: hydrogen-1 and helium-3. Hydrogen-1 has the smallest neutron number, 0.

Per Teodor Cleve

Per Teodor Cleve (10 February 1840 – 18 June 1905) was a Swedish chemist, biologist, mineralogist and oceanographer. He is best known for his discovery of the chemical elements holmium and thulium.Born in Stockholm in 1840, Cleve earned his BSc and PhD from Uppsala University in 1863 and 1868, respectively. After receiving his PhD, he became an assistant professor of chemistry at the university. He later became professor of general and agricultural chemistry. In 1874 he theorised that didymium was in fact two elements; this theory was confirmed in 1885 when Carl Auer von Welsbach discovered neodymium and praseodymium.

In 1879 Cleve discovered holmium and thulium. His other contributions to chemistry include the discovery of aminonaphthalenesulfonic acids, also known as Cleve's acids. From 1890 on he focused on biological studies. He developed a method of determining the age and order of late glacial and postglacial deposits from the types of diatom fossils in the deposits, and wrote a seminal text in the field of oceanography. He died in 1905 at age 65.

Praseodymium(III) bromide

Praseodymium(III) bromide is a crystalline compound of one praseodymium atom and three bromine atoms.

Praseodymium(III) chloride

Praseodymium(III) chloride is the inorganic compound with the formula PrCl3. It is a blue-green solid that rapidly absorbs water on exposure to moist air to form a light green heptahydrate.

Praseodymium(III) oxide

Praseodymium(III) oxide, praseodymium oxide or praseodymia is the chemical compound composed of praseodymium and oxygen with the formula Pr2O3. It forms white hexagonal crystals. Praseodymium(III) oxide crystallizes in the manganese(III) oxide or bixbyite structure.

Praseodymium(III) sulfate

Praseodymium(III) sulfate is a praseodymium compound with formula Pr2(SO4)3. It is an odourless whitish-green crystalline compound. The anhydrous substance readily absorbs water forming pentahydrate and octahydrate.

Praseodymium(III) sulfide

Praseodymium(III) sulfide is an inorganic chemical compound with chemical formula Pr2S3.

Conditions/substances to avoid are: heat, moisture, acids, flame and thin foils.

Praseodymium (III,IV) oxide

Praseodymium (III,IV) oxide is the inorganic compound with the formula Pr6O11 that is insoluble in water. It has a cubic fluorite structure. It is the most stable form of praseodymium oxide at ambient temperature and pressure.

Praseodymium oxide

Praseodymium oxide may refer to:

Praseodymium(III) oxide (dipraseodymium trioxide), Pr2O3

Praseodymium(IV) oxide (praseodymium dioxide), PrO2

Praseodymium(III,IV) oxide, Pr6O11

Propyl group

In organic chemistry, propyl is a three-carbon alkyl substituent with chemical formula –CH2CH2CH3 for the linear form. This substituent form is obtained by removing one hydrogen atom attached to the terminal carbon of propane. A propyl substituent is often represented in organic chemistry with the symbol Pr (not to be confused with the element praseodymium).

An isomeric form of propyl is obtained by moving the point of attachment from a terminal carbon atom to the central carbon atom, named 1-methylethyl or isopropyl. To maintain four substituents on each carbon atom, one hydrogen atom has to be moved from the middle carbon atom to the carbon atom which served as attachment point in the n-propyl variant, written as –CH(CH3)2.Linear propyl is sometimes termed normal and hence written with a prefix n- (i.e., n-propyl), as the absence of the prefix n- does not indicate which attachment point is chosen, i.e. absence of prefix does not automatically exclude the possibility of it being the branched version (i.e. i-propyl or isopropyl).In addition, there is a third, cyclic, form called cyclopropyl, or c-propyl. It is not isomeric with the other two forms, having the chemical formula -C3H5.