|Name, symbol, number||promethium, Pm, 61|
|Group, period, block||n/a, 6, f|
|Standard atomic weight|| g·mol−1|
|Electron configuration||[Xe] 4f5 6s2|
|Electrons per shell||2, 8, 18, 23, 8, 2 (Image)|
|Density (near r.t.)||7.26 g·cm−3|
|Melting point||1315 K, 1042 °C, 1908 °F|
|Boiling point||3273 K, 3000 °C, 5432 °F|
|Heat of fusion||7.13 kJ·mol−1|
|Heat of vaporization||289 kJ·mol−1|
|Oxidation states||3 (mildly basic oxide)|
|Electronegativity||? 1.13 (Pauling scale)|
|Ionization energies||1st: 540 kJ·mol−1|
|2nd: 1050 kJ·mol−1|
|3rd: 2150 kJ·mol−1|
|Atomic radius||183 pm|
|Covalent radius||199 pm|
|Electrical resistivity||(r.t.) est. 0.75 µΩ·m|
|Thermal conductivity||(300 K) 17.9 W·m−1·K−1|
|Thermal expansion||(r.t.) (α, poly)
est. 11 µm/(m·K)
|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 registry number||7440-12-2|
|Most stable isotopes|
|Main article: Isotopes of promethium|
Promethium (pronounced /prɵˈmiːθiəm/, pro-MEE-thee-əm) is a chemical element with the symbol Pm and atomic number 61. It is notable for being the only other exclusively radioactive element besides technetium which is followed by chemical elements that have stable isotopes.
The existence of promethium was first predicted by Bohuslav Brauner in 1902. During his research on the chemical properties of rare earth elements he found that the difference between neodymium and samarium is larger than between the other lanthanides. This prediction was supported in 1914 by Henry Moseley who, having discovered that atomic number was an experimentally measurable property of elements, found that no known element had atomic number 61. With the knowledge of a gap in the periodic table several groups started to search for the new element in natural environment.
The first discovery was published by Italian scientists Luigi Rolla and Lorenzo Fernandes from Florence. After separating a didymium nitrate concentrate from the Brazilian mineral monazite, which contained 70% dysprosyium and neodymium with the other lantanoides making up the additional 30%, by fractionated crystallisation, they yielded a solution containing mostly samarium. This solution gave x-ray spectra attributed to samarium and element 61. In honor of their city they named element 61 Florentium. The results were published in 1926, but the scientists claimed that the experiments were done in 1924. In the same year 1926 a group of scientists University of Illinois at Urbana-Champaign Smith Hopkins and Len Yntema published the discovery of element 61. They named it after the university illinium. Neither of the two discoveries could be verified.
So several groups claimed to have produced the element, but they could not confirm their discoveries because of the difficulty of separating promethium from other elements. Promethium was first produced and proved to exist at Oak Ridge National Laboratory (ORNL) in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell by separation and analysis of the fission products of uranium fuel irradiated in the Graphite Reactor; however, being too busy with defense-related research during World War II, they did not announce their discovery until 1947. The name promethium is derived from Prometheus, the Titan, in Greek mythology, who stole the fire from Mount Olympus and brought it down to mankind. The name was suggested by Grace Mary Coryell, Charles Coryell's wife, who felt that they were stealing fire from the gods.
Today, promethium is still recovered from the byproducts of uranium fission; it can also be produced by bombarding 146Nd with neutrons, turning it into 147Nd which decays into 147Pm through beta decay with a half-life of 11 days.
Promethium can be formed in nature as a product of spontaneous fission of uranium-238 and alpha decay of europium-151. Only trace amounts can be found in naturally occurring ores: a sample of pitchblende has been found to contain promethium at a concentration of four parts per quintillion (1018) by mass. It was calculated that the equilibrium mass of promethium in the earth's crust is about 560 g due to uranium fission and about 12 g due to the recently observed alpha decay of europium-151.
Promethium's longest lived isotope 145Pm is a soft beta emitter with a half-life of 17.7 years. It does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays, and a sample of 145Pm does produce some such soft X-ray radiation in addition to beta particles.
Pure promethium exists in two allotropic forms, and its chemistry is similar to other lanthanides. Promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity. Promethium can be found in traces in some uranium ores, as a fission product. Newly made promethium is also seen in the spectra of some stars.
Promethium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form promethium hydroxide:
Promethium metal reacts with all the halogens:
Thirty-six radioisotopes of promethium have been characterized, with the most stable being 145Pm with a half-life of 17.7 years, 146Pm with a half-life of 5.53 years, and 147Pm with a half-life of 2.6234 years. All of the remaining radioactive isotopes have half-lives that are less than 364 days, and the majority of these have half lives that are less than 27 seconds. This element also has 11 meta states with the most stable being 148Pmm (T½ 41.29 days), 152Pmm2 (T½ 13.8 minutes) and 152Pmm (T½ 7.52 minutes).
The isotopes of promethium range in atomic weight from 127.9482600 u (128Pm) to 162.9535200 u (163Pm). The primary decay mode before the longest-lived isotope, 145Pm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 145Pm are neodymium (Nd) isotopes and the primary products after are samarium (Sm) isotopes.
Along with technetium, promethium is one of only two elements with atomic number less than 83 that have only unstable isotopes, which is a rarely occurring effect of the liquid drop model and stabilities of neighbor element isotopes.
Uses for promethium include:
Promethium must be handled with great care because of its high radioactivity. In particular, promethium can emit X-rays during its beta decay. Its half-life is less than that of plutonium-239 by a factor of about 1350, and its biological toxicity is correspondingly higher. Promethium has no biological role.
Promethium compounds include:
Promethium is a chemical element that has the symbol Pm on the periodic table. It has the atomic number 61 which means it has 61 protons in its atom. It is a Lanthanide. All its isotopes are radioactive. Together with Technetium, these are the only two radioactive elements below lead. Most Promethium is artificially produced, and has between 141 and 156 protons. The longest-living promethium is 145Pm, with a half-life of 17.7 years.
Promethium is used in the illuminated digits of some clocks, its beta radiation may be used to measure thickness.