Tm
Thulium
Element 69 · Lanthanide
Thulium (Tm)
Thulium is the second rarest naturally occurring lanthanide. It is used in portable X-ray machines and lasers.
- Lanthanide
- Period 6
- f-block series
- f-block
- solid at room temperature
Key properties
- Atomic mass
- 168.9342
- u
- Electron configuration
- [Xe] 4f13 6s2
- Melting point
- 1,544.9 °C
- 1,818 K
- Boiling point
- 1,949.9 °C
- 2,223 K
- Density
- 9.32 g/cm³
- Electronegativity
- 1.25
- Pauling
- Atomic radius
- 227 pm
- van der Waals
- 1st ionisation energy
- 6.184 eV
Compare with every element:Electronegativity chartAtomic radius chartIonisation energy chartDensity chart of the elementsMelting point chartElectron configuration chart
Did you know?
Notable facts about thulium
- 01
Pure thulium was not made until 1911, after about 15,000 recrystallisations.
- 02
Euro banknotes use thulium’s blue fluorescence under UV light.
- 03
Thulium-170 is used as a radiation source in portable X-ray devices.
Applications
What is thulium used for?
- Portable X-ray sources
- Surgical lasers
- Anti-counterfeiting inks
- Ceramic superconductors
History
Discovery & name origin
Discovered by
Year
Where
Sweden
Name origin
From Thule, an ancient name for the far north.
Atomic structure
Atomic properties
Atomic structure
Atomic properties
- Atomic number
- 69
- Atomic mass
- 168.9342 u
- Group
- Lanthanides (3)
- Period
- 6
- Block
- f-block
- Electron configuration
- [Xe] 4f13 6s2
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f13
- Electrons per shell
- 2, 8, 18, 31, 8, 2
- Electronegativity (Pauling)
- 1.25
- Electron affinity
- —
- Atomic radius (van der Waals)
- 227 pm
- Stable isotopes
- 1
Oxidation states
Highlighted: common oxidation states (+3).
Successive ionisation energies
Energy to remove each electron in turn (kJ/mol). Big jumps show where a new, inner shell begins.
- 1st596.7
- 2nd1,160
- 3rd2,285
- 4th4,120
Physical
Physical properties & colour
Physical
Physical properties & colour
- State at 20 °C
- Solid
- Melting point
- 1,818 K · 1,544.9 °C · 2,812.7 °F
- Boiling point
- 2,223 K · 1,949.9 °C · 3,541.7 °F
- Density
- 9.32 g/cm³
- Molar heat capacity
- 27.03 J/(mol·K)
- Appearance
- Silvery grey
- CPK model colour
- Copied
The CPK colour is the convention used for this element’s atoms in molecular models.
FAQ
Thulium questions
What is Tm on the periodic table?
Tm is the symbol for thulium, element 69 on the periodic table. It sits in period 6, in the f-block, in the lanthanide category, and has an atomic mass of 168.9342.
What is the atomic number of thulium?
Thulium has atomic number 69, so every thulium atom has 69 protons in its nucleus. Its symbol is Tm and its atomic mass is 168.9342.
Who discovered thulium?
Thulium was discovered by Per Teodor Cleve in 1879 (Sweden). The name comes from from Thule, an ancient name for the far north.
What is thulium used for?
Thulium is used for: portable X-ray sources; surgical lasers; anti-counterfeiting inks; ceramic superconductors.
Is thulium a metal?
Yes. Thulium is a lanthanide, one of the metallic elements.
What is the electron configuration of thulium?
The electron configuration of thulium is [Xe] 4f13 6s2. Its 69 electrons are arranged in shells as 2, 8, 18, 31, 8, 2.