Promethium

Promethium, ₆₁Pm
Promethium
Pronunciation	/proʊˈmiːθiəm/ (proh-MEE-thee-əm)
Appearance	metallic
Mass number	[145]
Promethium in the periodic table
	neodymium ← promethium → samarium
Atomic number (Z)	61
Group	f-block groups (no number)
Period	period 6
Block	f-block
Electron configuration	[Xe] 4f5 6s2
Electrons per shell	2, 8, 18, 23, 8, 2
Physical properties
Phase at STP	solid
Melting point	1315 K (1042 °C, 1908 °F)
Boiling point	3273 K (3000 °C, 5432 °F)
Density (at 20° C)	α-145Pm: 7.149 g/cm3; α-147Pm: 7.247 g/cm3
Heat of fusion	7.13 kJ/mol
Heat of vaporization	289 kJ/mol
Atomic properties
Oxidation states	+2, +3 (a mildly basic oxide)
Electronegativity	Pauling scale: 1.13 (?)
Ionization energies	1st: 540 kJ/mol ; 2nd: 1050 kJ/mol ; 3rd: 2150 kJ/mol ; ;
Atomic radius	empirical: 183 pm
Covalent radius	199 pm
	Spectral lines of promethium
Other properties
Natural occurrence	from decay
Crystal structure	double hexagonal close-packed (dhcp) (hP4)
Lattice constants	a = 0.36393 pm; c = 1.1739 pm (at 20 °C)
Thermal expansion	9.0×10−6/K (at r.t.)
Thermal conductivity	17.9 W/(m⋅K)
Electrical resistivity	est. 0.75 µΩ⋅m (at r.t.)
Magnetic ordering	paramagnetic
Young's modulus	α form: est. 46 GPa
Shear modulus	α form: est. 18 GPa
Bulk modulus	α form: est. 33 GPa
Poisson ratio	α form: est. 0.28
CAS Number	7440-12-2
History
Discovery	Charles D. Coryell, Jacob A. Marinsky, Lawrence E. Glendenin (1945)
Named by	Grace Mary Coryell (1945)
Isotopes of promethium v; e;
α	141Pr
β−	146Sm
	Category: Promethium; view; talk; edit; \| references

Promethium is a chemical element; it has symbol Pm and atomic number 61. All of its isotopes are radioactive; it is extremely rare, with only about 500–600 grams naturally occurring in Earth's crust at any given time. Promethium is one of only two radioactive elements that are followed in the periodic table by elements with stable forms, the other being technetium. Chemically, promethium is a lanthanide. Promethium shows only one stable oxidation state of +3.

In 1902 Bohuslav Brauner suggested that there was a then-unknown element with properties intermediate between those of the known elements neodymium (60) and samarium (62); this was confirmed in 1914 by Henry Moseley, who, having measured the atomic numbers of all the elements then known, found that atomic number 61 was missing. In 1926, two groups (one Italian and one American) claimed to have isolated a sample of element 61; both "discoveries" were soon proven to be false. In 1938, during a nuclear experiment conducted at Ohio State University, a few radioactive nuclides were produced that certainly were not radioisotopes of neodymium or samarium, but there was a lack of chemical proof that element 61 was produced, and the discovery was not generally recognized. Promethium was first produced and characterized at Oak Ridge National Laboratory in 1945 by the separation and analysis of the fission products of uranium fuel irradiated in a graphite reactor. The discoverers proposed the name "prometheum" (the spelling was subsequently changed), derived from Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to humans, to symbolize "both the daring and the possible misuse of mankind's intellect". However, a sample of the metal was made only in 1963.

The two sources of natural promethium are rare alpha decays of natural europium-151 (producing promethium-147) and spontaneous fission of uranium (various isotopes). Promethium-145 is the most stable promethium isotope, but the only isotope with practical applications is promethium-147, chemical compounds of which are used in luminous paint, atomic batteries and thickness-measurement devices. Because natural promethium is exceedingly scarce, it is typically synthesized by bombarding uranium-235 (enriched uranium) with thermal neutrons to produce promethium-147 as a fission product.

^ ^a ^b ^c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
^ Cverna, Fran (2002). "Ch. 2 Thermal Expansion". ASM Ready Reference: Thermal properties of metals (PDF). ASM International. ISBN 978-0-87170-768-0.
^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

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[Arblaster_2018-1] Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.

[2] Cverna, Fran (2002). "Ch. 2 Thermal Expansion". ASM Ready Reference: Thermal properties of metals (PDF). ASM International. ISBN 978-0-87170-768-0.

[magnet-4] Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.

[NUBASE2020-5] Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

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