Promethium (Pm)

Promethium is a chemical element with symbol Pm and atomic number 61. All of its isotopes are radioactive; it is one of only two such elements that are followed in the periodic table by elements with stable forms.

Atomic Number

61

Atomic Mass

145 u

Category

lanthanide

Phase

solid

Density

7.26 g/cm³

Electron Shells

2, 8, 18, 23, 8, 2

Atomic Structure

Protons: 61 • Electrons: 61 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁵

Discovery

1945 • Jacob A. Marinsky, Lawrence E. Glendenin, Charles D. Coryell