Periodic table › Thulium
Thulium — Tm
Lanthanoid · Group Lanthanoid (f-block) · Period 6
Open the 3D atom, orbital and crystal lab →1. Identity and classification
Silvery-white, malleable, electropositive rare-earth metal that tarnishes in air
- Name and symbol
- Thulium (Thulium) · Tm
- Atomic number
- 69
- Relative atomic weight / mass number
- 168.93 ± 0.01
- Group · period · block
- Lanthanoid (f-block) · 6 · f
- Category
- Lanthanoid
- State near room temperature
- Solid
- Stable isotopes
- At least one stable isotope
- CAS number
- 7440-30-4
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 69 · 69
- Neutrons in reference isotope
- 100 (169Tm)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹³ 6s²- Abbreviated configuration
[Xe]6s² 4f¹³- Electrons per shell
- 2, 8, 18, 31, 8, 2
- Listed oxidation states
- +3
- Electronegativity
- 1.25 (Pauling)
- First ionization energy
- 596.665 kJ/mol · 6.184 eV
- Electron affinity
- Not established
- Covalent radius
- 190 pm
- van der Waals radius
- 227 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- 9.32 g/cm³
- Melting point
- 1818 K · 1544.85 °C · 2812.73 °F
- Boiling point
- 2223 K · 1949.85 °C · 3541.73 °F
- Crystal structure
- HCP
- Specific heat
- 0.16 J/(g·K)
- Thermal conductivity
- 16.9 W/(m·K)
- Enthalpy of fusion
- 16.84 kJ/mol
- Enthalpy of vaporization
- 247 kJ/mol
- Magnetic ordering
- Paramagnetic
- Mohs hardness
- Not established
- Speed of sound
- Not established
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The +3 state is common in this series, with important element-specific exceptions.
Selected compounds: TmO / Tm₂O₃ (Oxide) · TmClₙ (Chloride) · TmFₙ (Fluoride)
Reaction reference
Many members oxidize in air; behavior depends on the element and oxidation state.
Water reactivity varies across this series and with surface conditions.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 169Tm | Stable | 100% | Stable |
| 170Tm | Radioactive | — | 128.6 d |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- 1879 CE
- Scientists associated with discovery
- Per Teodor Cleve
- Location
- Sweden (Uppsala)
- Origin
- Natural
- Listed crustal abundance
- Not established
Minerals and naming reference
Xenotime, Monazite (rarest stable rare-earth element)
Named from scientific/historical roots associated with Thulium (Tm), discovered or characterized by Per Teodor Cleve.
7. Applications
Portable medical/industrial X-ray sources (¹⁷⁰Tm), Thulium fiber surgical lasers, Euro banknote UV security fluorescence
Detailed applications by field
- everyday
- Portable medical/industrial X-ray sources (¹⁷⁰Tm), Thulium fiber surgical lasers, Euro banknote UV security fluorescence
- industry
- Used in lanthanoid processing, specialized alloys, and chemical manufacturing (Portable medical/industrial X-ray sources (¹⁷⁰Tm), Thulium fiber surgical lasers, Euro banknote UV security fluorescence).
- electronics
- Applied in electronic components, semiconductors, or functional coatings where Thulium's electronic structure ([Xe] 4f¹³ 6s²) provides target conductivity.
- medicine
- Diagnostic imaging, biomedical instrumentation, or pharmaceutical synthesis research.
- energy
- Utilized in power generation, battery materials, catalysts, or nuclear technology involving Thulium.
- aerospace
- High-performance materials, structural alloys, or space instrumentation utilizing Thulium.
- agriculture
- Soil geochemistry analysis, trace micronutrient research, or analytical environmental monitoring.
- science
- Spectroscopic standard, crystallography, and quantum chemistry studies of Period 6 f-block elements.
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Classified as non-essential in human and biological systems.