| Tecken | Pm |
| Atomnummer | 61 |
| Grupp | - |
| Period | 6 |
| Block | f |
| Ämnesklass | Lantanoid |
| Utseende | Metallic |
| Färg | Silver |
| Antal protoner | 61 p+ |
| Antal neutroner | 84 n0 |
| Antal elektroner | 61 e- |
| Fas vid STP | Fast |
| Densitet | 7.26 g/cm3 |
| Relativ atommassa | 145 u |
| Smältpunkt | 1315 K 1041.85 °C 1907.33 °F |
| Kokpunkt | 3273 K 2999.85 °C 5431.73 °F |
| Ångbildningsvärme | 289 kJ/mol |
| Elektronegativitet (Paulingskalan) | 1.13 |
| Elektronaffinitet | 12.45 kJ/mol |
| Oxidationstal | +2, +3 (a mildly basic oxide) |
| Jonisationspotential |
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| Upptäckt | Charles D. Coryell, Jacob A. Marinsky, Lawrence E. Glendenin (1945) |
| Namngivare | Grace Mary Coryell (1945) |
Upptäckten av prometium 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. | |