Promethium
Chemical element
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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. Wikipedia
Symbol: Pm
Discovered: 1945
Atomic number: 61
Electron configuration: [Xe] 4f⁵ 6s²
Atomic mass: 145 u
Discoverers: Jacob A. Marinsky, Charles D. Coryell, and Lawrence E. Glendenin
Melting point: 1,907°F (1,042°C)