The name protactinium means "before actinium". This is because a uranium atom decays to form a protactinium atom, which then rapidly decays into an actinium atom. Small amounts of protactinium are found in ancient sands and muds. Geologists use Geiger counters to conduct research to calculate the age of sands.

Summary of properties (Pa)

Atomic weight231.03588(1)
Discoverer (year)Soddy, Frederick; Cranston, John & Hahn, Otto (1913)
Natural formmetallic solid (tetragonal)
Electron configuration[Rn] 52 6d1 7s2
Melting point (ºC)1568
Boiling point (ºC)
Abundance in earth's crust (ppm)<0.001
Isotope (abundance)231Pa (100)
Density g/cm311.72
Van der Waals radius (pm)243
Covalent radius (pm)184
Electronegativity (Pauling)1.5
Vaporization enthalpy (kJ/mol)481.00
Enthalpy of fusion (kJ/mol)12.34
Specific heat capacity (J/g·K) at 25ºC and 1 atm-
Thermal conductivity (W/cm·K) at 25ºC and 1 atm-
Oxidation state+5, +4
Electron affinity (eV)
1st Ionization potential (eV)5.8900

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