Thulium (Tm)

Thulium is a chemical element with symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series.

Atomic Number

69

Atomic Mass

168.93 u

Category

lanthanide

Phase

solid

Density

9.32 g/cm³

Electron Shells

2, 8, 18, 31, 8, 2

Atomic Structure

Protons: 69 • Electrons: 69 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹³

Discovery

1879 • Per Teodor Cleve