About

Promethium is an extremely rare, radioactive rare-earth metal, with all its isotopes being unstable. It is one of only two radioactive elements followed in the periodic table by stable elements. It is used in luminous paints for watches and signs that glow in the dark without external energy, and in specialized atomic batteries for spacecraft and missiles where long life is required.

Atomic Properties

Atomic Number61

Atomic Weight144.913 u

Neutrons (common)84

Electron Configuration[Xe] 4f⁵ 6s²

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁵ 5s² 5p⁶ 6s²

Electrons per Shell2, 8, 18, 23, 8, 2

Electronegativity1.13

Electron Affinity12.4 kJ/mol

Oxidation States+3

Ionic Radius97.9 pm

Periodic Table Position

Group3

Period6

BlockF

Chemical SeriesLanthanoids

Physical Properties

State at STPsolid

AppearanceSilvery white metallic

Density at STP7.26 g/cm³

Crystal Structurehexagonal

Magnetic Orderingparamagnetic

Thermal Properties

Melting Point1,315 K

Boiling Point3,273 K

Thermal Conductivity15 W/(m·K)

Specific Heat0.185 J/(g·K)

Molar Heat26.8 J/(mol·K)

Heat of Fusion7.13 kJ/mol

Heat of Vaporization289 kJ/mol

Abundance

In Earth's Crust0 ppm

Discovery

Discovered byJacob A. Marinsky, Lawrence E. Glendenin, Charles D. Coryell

Discovery Year1,945

Occurrencesynthetic

CAS Number7440-12-2

Electron Configuration

Energy

↿⇂

↿

Isotopes of Promethium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
¹⁴⁵Pm	144.912740	—	17.7 y	Electron Capture
¹⁴⁶Pm	145.914690	—	5.53 y	Electron Capture, Beta Minus Decay
¹⁴⁷Pm	146.915130	Trace	2.6234 y	Beta Minus Decay

Interactive Visualization

Explore the 3D Bohr model of Promethium in our interactive viewer.

View 3D Model of Promethium