Thulium (Tm)
Thulium is element 69, a lanthanide in period 6 of the periodic table. At room temperature it is a solid.
Electron configuration [Xe] 4f13 6s2
Electrons per shell 2, 8, 18, 31, 8, 2
Thulium data
| Atomic number | 69 |
|---|---|
| Symbol | Tm |
| Atomic mass | 168.934 u |
| Category | Lanthanide |
| Group | — (f-block) |
| Period | 6 |
| Block | f |
| State at 25 °C | solid |
| Melting point | 1818 K (1544.9 °C) |
| Boiling point | 2223 K (1949.9 °C) |
| Density | 9.321 g/cm³ |
| Electronegativity (Pauling) | 1.25 |
| Atomic radius | — |
| 1st ionization energy | 597 kJ/mol |
| Electron affinity | -50 kJ/mol |
| Oxidation states | +2, +3 |
| Common ion charge | 3+ |
| Discovered | 1879 |
Orbital diagram
Each box is one orbital holding up to two electrons of opposite spin. Following Hund’s rule, electrons spread out singly across a subshell before pairing.
Work through thulium’s configuration and its ions →
Where thulium sits
Thulium belongs to the lanthanides. Its Pauling electronegativity of 1.25 is mid-range; see the electronegativity chart and periodic trends for context. To use its mass in a calculation, try the molar mass calculator.
Thulium FAQ
What is the electron configuration of thulium?
Thulium (Z = 69) has the configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f13 6s2. In noble-gas shorthand that is [Xe] 4f13 6s2.
How many valence electrons does thulium have?
2 (2 in the outer s subshell).
What is the atomic mass of thulium?
The standard atomic weight of thulium is 168.934 u, so one mole weighs 168.934 g.
Is thulium a metal?
Yes. Thulium is a lanthanide.
What is the charge of a thulium ion?
Thulium most commonly forms Tm3+.