Thulium (Tm)
Stable Isotopes of Thulium
| Isotope | Z(p) | N(n) | Atomic Mass | Natural Abundance | Nuclear Spin |
| Tm-169 | 69 | 100 | 168.934211 | 100.00% | 1/2+ |
Thulium was discovered in 1879 by Per Theodore Cleve. Its name derives from Thule, an ancient name for Scandinavia.
Thulium is a silvery-white metal with a metallic luster and a hexagonal, close-packed structure. Its salts are colored green. It has an effective magnetic moment of 7.62 Bohr magneton. It is insoluble in water and dissolves in concentrated acids. It is relatively stable in air at ambient temperatures. Reactions with halogens are slow at ordinary temperatures, but vigorous above 200 ºC, forming halides. Thulium reacts with concentrated mineral acids, forming corresponding salts and liberating hydrogen.
The metal has very few commercial applications because of its high cost and low relative abundance. Thulium metal pellets containing natural isotope Thulium-169 and radioactive isotope Thulium-170 are used in portable x-ray equipment as medical and dental diagnostic tools. These pellets are also used to detect flaws in small, inaccessible parts of mechanical and electrical devices. Radioactive Thulium-171 is a beta emitter with a half-life of two years and is potentially useful as an energy source. Natural thulium is used in ceramic magnetic materials (ferrites) for microwave devices.
Properties of Thulium
| Name | Thulium |
| Symbol | Tm |
| Atomic number | 69 |
| Atomic weight | 168.9342 |
| Standard state | Solid at 298 ºK |
| CAS Registry ID | 7440-30-4 |
| Group in periodic table | N/A |
| Group name | Lanthanoid |
| Period in periodic table | 6 (Lanthanoid) |
| Block in periodic table | f-block |
| Color | Silvery white |
| Classification | Metallic |
| Melting point | 1545 °C |
| Boiling point | 1947 °C |
| Vaporization point | 1947 °C |
| Thermal conductivity | 16.9 W/(m·K) at 298.2 ºK |
| Electrical resistivity | 79.0 µΩ·cm at 25 ºC |
| Electronegativity | 1.2 |
| Specific heat | 0.16 kJ/kg K |
| Heat of vaporization | 250 kJ·mol-1 |
| Heat of fusion | 16.8 kJ·mol-1 |
| Density of liquid | 8.56 g/cm3 at 1545 °C |
| Density of solid | 9.32 g/cm3 |
| Electron configuration | [Xe]4f136s2 |
| Atomic radius | 1.73 Å |
| Ionic radius | Tm3+: 1.09 Å (coordination number 7) |
| Oxidation states | +2, +3 |
| Most stable oxidation state | +3 |
