Protactinium
Chemical element
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Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, silvery-gray actinide metal which readily reacts with oxygen, water vapor, and inorganic acids. Wikipedia
Symbol: Pa
Atomic number: 91
Atomic mass: 231.03588 u
Discoverers: Kazimierz Fajans and Oswald Helmuth Göhring
Electron configuration: Rn 5f2 6d1 7s2
Melting point: 2,854°F (1,568°C)
Discovered: 1913