69 Tm 168.93
Thulium
Lanthanide
Thulium (Tm) is a chemical element with atomic number 69, classified as a lanthanide. At room temperature it is a solid. It was discovered in 1879 by Per Teodor Cleve.
Properties
- Atomic number
- 69
- Atomic mass
- 168.93 u
- Category
- Lanthanide
- Group
- 0
- Period
- 6
- Block
- f-block
- Electron configuration
- [Xe] 4f¹³ 6s²
- Phase at STP
- Solid
- Density
- 9.321 g/cm³
- Melting point
- 1818 K (1544.8 °C)
- Boiling point
- 2223 K (1949.8 °C)
- Electronegativity
- 1.25
- Atomic radius
- 222 pm
- Ionization energy
- 6.184 eV
- Discovery
- 1879 · Per Teodor Cleve
Common uses
Medical X-rays, lasers, research, portable X-ray machines
Did you know?
Least abundant rare earth element and used in portable X-ray devices.