Promethium

Chaitra 26/06/2026 19:58:08 Updated 26/06/2026 19:58:08

Property	Value
Atomic Number	61
Element	Promethium
Symbol	Pm
Atomic Mass	[145] (most stable isotope)
Number of Neutrons	84 (Promethium-145)
Number of Protons	61
Number of Electrons	61
Period	6
Group	Lanthanide (no fixed group number)
Phase	Solid
Radioactive	Yes
Natural	No (trace amounts occur in uranium ores)
Metal	Yes
Nonmetal	No
Metalloid	No
Type	Lanthanide
Atomic Radius	236 pm
Electronegativity	1.13 (Pauling scale)
First Ionization Energy	5.582 eV
Density	7.26 g/cm³ (estimated)
Melting Point	1042 °C
Boiling Point	3000 °C (estimated)
Number of Isotopes	No stable isotopes (Pm-145 most stable)
Discoverer	Jacob A. Marinsky, Lawrence E. Glendenin, Charles D. Coryell
Year	1945
Specific Heat	— (data not well established)
Number of Shells	6
Number of Valence Electrons	3