The first isotope of protactinium 234mPa was discovered by Kasimir Fajans and Otto Gohring in 1913 in Germany. The isotope 231Pa of protactinium was discovered by Austrian physicist Lise Meitner and by Otto Hahn, a German physical chemist in 1917/1918 and simultaneously by Frederick Soddy and John Cranston of Great Britain.
Name: Protactinium
Symbol: Pa
Atomic number: 91
Atomic weight: 231.04
State: solid
Group, period, block: n/a, 7, f
Color: bright, silvery metallic luster
Classification: actinide
Electron configuration: 5f2 6d1 7s2
2,8,18,32,20,9,2
Physical properties
Density: 15.37 g/cm-3
Melting point: 1841 K,1568 °C,2854 °F
Boiling point: 4300 K,4027 °C,7280 °F
Atomic properties
Oxidation states: 2, 3, 4, 5
Electronegativity: 1.5 (Pauling scale)
Ionization energies: 1st: 568 kJ·mol-1
Covalent radius: 200 pm
Van der Waals radius: no data
- Pa
Electron Configuration
Isotopes
Protactinium has no stable isotopes. 29 radioisotopes of protactinium have been characterized, with the most stable being 231Pa with a half-life of 32,760 years.