Quick answerThulium (Tm) is a lanthanide with atomic number 69 and an atomic mass of 168.93 (2023), in period 6. It was discovered by Per Teodor Cleve in 1879. It is used for surgical lasers and portable X-ray sources. Its electron configuration is [Xe] 4f13 6s2.
Thulium is the rarest stable lanthanide, and its lasers cut tissue in surgery while its isotopes X-ray welds.
Key facts
| Symbol | Tm |
|---|---|
| Atomic number | 69 |
| Atomic mass | 168.93 (IUPAC standard atomic weight, 2023) |
| Category | lanthanide |
| Group | — (f-block element, no group number) |
| Period | 6 |
| Block | f-block |
| Electron configuration | [Xe] 4f13 6s2 |
| Discovered | Per Teodor Cleve, 1879 |
| Uses | surgical lasers, portable X-ray sources, lasers, ceramics, high-temperature superconductors |
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Keep exploring
- Periodic table — all 118 elements
- Promethium (Pm) — another lanthanide, atomic number 61
- Samarium (Sm) — another lanthanide, atomic number 62
- Europium (Eu) — another lanthanide, atomic number 63
- Gadolinium (Gd) — another lanthanide, atomic number 64
- Terbium (Tb) — another lanthanide, atomic number 65
- Dysprosium (Dy) — another lanthanide, atomic number 66
- Holmium (Ho) — another lanthanide, atomic number 67
- Erbium (Er) — another lanthanide, atomic number 68
- Ytterbium (Yb) — another lanthanide, atomic number 70
- Lutetium (Lu) — another lanthanide, atomic number 71
- All lanthanide elements — on the periodic table
Sources & last updated
- CIAAW — Standard Atomic Weights
- PubChem Periodic Table
- Wikipedia — Timeline of chemical element discoveries
Last updated: . Figures are shown with their year; where sources disagree, the value is left out rather than estimated.