Thorium (Th)

Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only three radioactive elements that still occur naturally in large quantities as a primordial element.

Atomic Number

90

Atomic Mass

232.04 u

Category

actinide

Phase

solid

Density

11.7 g/cm³

Electron Shells

2, 8, 18, 32, 18, 10, 2

Atomic Structure

Protons: 90 • Electrons: 90 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 6d²

Discovery

1829 • Jöns Jakob Berzelius