Thulium (Tm)
Lanthanide · f-block · period 6
Soft, silvery-grey, workable metal.
Thulium (symbol Tm) is chemical element number 69, a lanthanide in the lanthanide series (f-block), period 6 of the periodic table. Its standard atomic weight is 168.93 and its electron configuration is [Xe] 4f13 6s2. At room temperature it is a solid. The rarest of the stable rare earths, named after Thule, a mythical far-northern land.
Properties
| Atomic number | 69 |
|---|---|
| Atomic mass | 168.93 |
| Category | Lanthanide |
| Block | f-block |
| Group · Period | f-block series · 6 |
| Electron configuration | [Xe] 4f13 6s2 |
| Electrons per shell | 2, 8, 18, 31, 8, 2 |
| State at 25 °C | solid |
| Melting point | 1818 K |
| Boiling point | 2223 K |
| Density | 9.32 g/cm³ |
| Electronegativity (Pauling) | 1.25 |
| Radioactive | No |
| Origin | primordial |
| Discovered | 1879 · Per Teodor Cleve |
Key facts about Thulium
- The rarest of the stable rare earths, named after Thule, a mythical far-northern land.
- When irradiated in a reactor it becomes a portable X-ray source for field radiography.
- Thulium fibre lasers are compact and efficient, used in surgery and materials processing.
- Was once the most expensive rare earth because it was so hard to separate.
What Thulium is used for
Portable X-ray sources, high-efficiency surgical lasers, blue phosphors, high-temperature superconductors.
Where it sits in the periodic table
Thulium is in the lanthanide series, period 6, of the f-block. Its electron configuration [Xe] 4f13 6s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Thulium on the interactive table →
Thulium — frequently asked questions
What is Thulium used for?
Portable X-ray sources, high-efficiency surgical lasers, blue phosphors, high-temperature superconductors.
Is Thulium radioactive?
No. Thulium has at least one stable isotope and is not radioactive.
What is the electron configuration of Thulium?
Thulium has the electron configuration [Xe] 4f13 6s2, which is 2, 8, 18, 31, 8, 2 electrons per shell.
What group and period is Thulium in?
Thulium is in the lanthanide series (f-block), period 6, in the f-block. Its outer shell holds 2 electrons.
Who discovered Thulium?
Thulium was discovered in 1879 by Per Teodor Cleve.