Thulium
[Xe] 4f¹³ 6s² · 2 · 8 · 18 · 31 · 8 · 2
The rarest of the stable lanthanides and one of the dearest. Thulium is named after Thule, the mythical land at the edge of the world beyond which the ancients believed no ship sailed.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
Drag to rotate, scroll to zoom
Atomic properties
- Atomic number
- 69
- Atomic mass
- 168.934 а.е.м.
- Electron configuration
- [Xe] 4f¹³ 6s²
- Electrons per shell
- 2 · 8 · 18 · 31 · 8 · 2
- Block
- f-block
- Group
- no data
- Period
- 6
- Electronegativity (Pauling)
- 1.25
- Electronegativity (Allen)
- 1.11
- Atomic radius
- 227 pm
- Covalent radius
- 190 pm
- Van der Waals radius
- 227 pm
- Ionisation energy 1
- 596.7 kJ/mol
- Ionisation energy 2
- 1 160 kJ/mol
- Ionisation energy 3
- 2 285 kJ/mol
- Ionisation energy 4
- 4 120 kJ/mol
- Electron affinity
- 50 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 9.32 g/cm³
- Melting point
- 1 818 K · 1 544.9 °C
- Boiling point
- 2 223 K · 1 949.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 16.84 kJ/mol
- Heat of vaporisation
- 247 kJ/mol
- Specific heat capacity
- 0.16 J/(g·K)
- Thermal conductivity
- 16.9 W/(m·K)
Mechanical properties
- Young's modulus
- 74 GPa
- Shear modulus
- 30.5 GPa
- Bulk modulus
- 44.5 GPa
- Poisson ratio
- 0.21
- Mohs hardness
- no data
- Brinell hardness
- 471 MPa
Electrical and magnetic properties
- Electrical resistivity
- 676 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- 32 K
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 353.75 pm · c = 555.4 pm
Abundance
- In the crust
- 0.52 mg/kg
- In the ocean
- 1.7·10⁻⁷ mg/L
- In the universe
- 0.01 mg/kg
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 169Tm | 100 % | stable | — |
Thulium-169 is the only stable isotope. Thulium-170, half-life 128 days, emits soft X-rays and powers portable radiography sets.
Discovery
- Year of discovery
- 1879
- Discovered by
- Per Teodor Cleve
- Where
- Sweden
- Origin of the name
- from Thule, the mythical land of the far north
History
Per Cleve isolated thulium oxide in 1879 while continuing to take apart Mosander's erbium earth. Pure metal waited until 1911, after tens of thousands of recrystallisations.
Where it occurs
0.52 mg/kg of the crust — the scarcest lanthanide by mass fraction, though there is more of it in the crust than of gold.
How it is produced
By ion-exchange separation of heavy rare earths. Output is a few tonnes a year.
Role in living things
No biological role.
Safety
Of low toxicity, but thulium-170 needs radiation shielding: it is that isotope, not the element, that sets the safety requirements for working with it.
Uses
- Thulium-170 as a portable X-ray source for field radiography
- Thulium fibre lasers in surgery and industrial materials processing
- Doping scintillators and dosimeters
- Blue phosphor for the security marks on euro banknotes
Curiosities
- Thulium is the rarest lanthanide, artificial promethium aside.
- A thulium-170 X-ray set needs no power supply and works in the field.
- The name comes from Ultima Thule, the limit of the world known to the ancients.
- Thulium fibre lasers are displacing holmium ones in urology thanks to sharper absorption in water.