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.
Experiment with the elements
Thulium doesn't form any compounds in our lab yet, but the periodic table sandbox lets you combine dozens of other real elements into real compounds — water, table salt, ammonia and many more — with their true chemical formulas.