91
Pa
231.04
Protactinium
Element 91 · 231.04 u · f-block
actinide
One of the rarest and most expensive naturally occurring elements. Highly radioactive and toxic.
Phase (STP)
Solid
Melting Point
1572 °C
Boiling Point
4000 °C
Density
15.37 g/cm³
Electronegativity
1.5
Atomic Radius
180 pm
Ionization Energy
568 kJ/mol
Electron Affinity
—
Discovered
1913 · Kasimir Fajans
Electron Configuration
[Rn] 5f2 6d1 7s2
Electron Orbitals
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