69168.93TmThulium
Thulium (Tm) — element 69lanthanide · period 6
Thulium is a chemical element with the symbol Tm and atomic number 69. It is a lanthanide in period 6 of the periodic table (the f-block), with a standard atomic mass of 168.93 u. At room temperature (25 °C) thulium is a solid.
💡 Known for: One of the rarest lanthanides; used in portable X-ray devices and lasers.
# Thulium properties
| Symbol | Tm |
|---|---|
| Atomic number | 69 |
| Atomic mass | 168.93 u |
| Category | lanthanide |
| Group | — (f-block, no group number) |
| Period | 6 |
| Block | f-block |
| Electron configuration | [Xe] 4f¹³ 6s² |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹³ 5s² 5p⁶ 6s² |
| Electrons per shell | 2, 8, 18, 31, 8, 2 |
| Protons / electrons | 69 / 69 |
| State at 25 °C | solid |
| Melting point | 1818 K (1544.8 °C, 2812.7 °F) |
| Boiling point | 2223 K (1949.8 °C, 3541.7 °F) |
| Density | 9.321 g/cm³ |
| Electronegativity (Pauling) | 1.25 |
| First ionization energy | 6.184 eV |
| Atomic radius | 222 pm |
| Discovered | 1879 |
# Electron configuration of thulium
The electron configuration of thulium is [Xe] 4f¹³ 6s², written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹³ 5s² 5p⁶ 6s². Its 69 electrons fill 6 shells as 2, 8, 18, 31, 8, 2, so the outermost shell holds 2 electrons.
# Related elements
ErErbiumprevious elementYbYtterbiumnext elementLaLanthanumlanthanideCeCeriumlanthanidePrPraseodymiumlanthanideNdNeodymiumlanthanidePmPromethiumlanthanideSmSamariumlanthanideEuEuropiumlanthanideGdGadoliniumlanthanide
# Thulium FAQ
What is the atomic number of thulium?
The atomic number of thulium is 69: every thulium atom has 69 protons in its nucleus. Its symbol is Tm.
What is the atomic mass of thulium?
The standard atomic mass of thulium is 168.93 u.
What is the electron configuration of thulium?
Thulium's electron configuration is [Xe] 4f¹³ 6s² (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹³ 5s² 5p⁶ 6s²), with 2, 8, 18, 31, 8, 2 electrons per shell.
Is thulium a metal?
Yes. Thulium is a lanthanide, one of the metals.
What is the melting point of thulium?
Thulium melts at 1818 K (1544.8 °C, 2812.7 °F) and boils at 2223 K (1949.8 °C, 3541.7 °F).
What is thulium used for / known for?
One of the rarest lanthanides; used in portable X-ray devices and lasers.