Protactinium

Chaitra 26/06/2026 19:58:09 Updated 26/06/2026 19:58:09

Property	Value
Atomic Number	91
Element	Protactinium
Symbol	Pa
Atomic Mass	231.036 u
Number of Neutrons	140 (most common isotope, Protactinium-231)
Number of Protons	91
Number of Electrons	91
Period	7
Group	Actinide (no fixed group number)
Phase	Solid
Radioactive	Yes
Natural	Yes (found in uranium ores)
Metal	Yes
Nonmetal	No
Metalloid	No
Type	Actinide
Atomic Radius	~243 pm (estimated)
Electronegativity	1.50 (estimated)
First Ionization Energy	5.89 eV (estimated)
Density	15.37 g/cm³
Melting Point	1568 °C
Boiling Point	4027 °C (estimated)
Number of Isotopes	No stable isotopes (Pa-231 most notable)
Discoverer	Kasimir Fajans, Oswald Helmuth Göhring
Year	1913
Specific Heat	— (not well established)
Number of Shells	7
Number of Valence Electrons	5