Atomic number 69
Thulium
Lanthanide
In the real world
Quick facts
- Atomic mass
- 168.93
- Group
- –
- Period
- 6
- State (STP)
- solid
- Electronegativity
- 1.25
- Common ox. states
- +3
Properties
Electron configuration
[Xe] 4f¹³ 6s²
- Ionization energy
- 596.7 kJ/mol
- Electron affinity
- 50.0 kJ/mol
- Melting point
- 1818.00 K (1544.8 °C)
- Boiling point
- 2223.00 K (1949.8 °C)
How dangerous is it?
1/5 · Low risk
The rarest of the stable rare earths, used in portable X-ray sources and certain lasers. Low toxicity, with the same flammable-powder note as its neighbors.
- FlammableImmediate
Thulium filings can ignite in air; the solid metal stays stable. (as filings or powder, not the solid)
Handle powder away from flame; the solid metal needs no special precautions.
How it bonds· family overview
Thulium (Tm) is a lanthanide - a soft, silvery metal that almost always loses 3 electrons to form a +3 ion (Ln³⁺). Its 4f electrons sit deep below the valence shell, so chemistry across the lanthanide row is remarkably similar: oxide, fluoride, chloride salts, all in the +3 state.
