Protactinium (Pa)

Protactinium is a chemical element with symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids.

Atomic Number

91

Atomic Mass

231.04 u

Category

actinide

Phase

solid

Density

15.37 g/cm³

Electron Shells

2, 8, 18, 32, 20, 9, 2

Atomic Structure

Protons: 91 • Electrons: 91 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f² 6d¹

Discovery

1917 • Lise Meitner, Otto Hahn