Thulium
Definition and meaning of Thulium in chemistry.
Thulium is a chemical element with the symbol Tm and atomic number 69. It is the second least abundant of the lanthanides and is a bright, silvery-gray metal that can be easily worked and cut with a knife. The metal is reasonably stable in air but must be protected from moisture to prevent slow degradation.
In more detail
Thulium is primarily extracted from monazite and bastnasite ores alongside other rare earths, though it occurs in extremely low concentrations (about 0.5 parts per million in the Earth's crust). Located late in the f-block of the periodic table, it behaves similarly to its neighboring lanthanides, forming compounds almost exclusively in the +3 oxidation state. The element burns in air at high temperatures to form thulium(III) oxide and dissolves readily in dilute acids to form pale green solutions. When bombarded in a nuclear reactor, natural thulium-169 produces the radioactive isotope thulium-170, which emits X-rays. Because of its scarcity and high extraction cost, the metal has very few commercial applications outside of specialized research. However, its unique emission spectrum makes it valuable for anti-counterfeiting features in currency and in specialized laser systems.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Tm |
| Atomic number | 69 |
| Atomic mass | 168.93 u |
| Category | Lanthanide |
| State at room temperature | Solid |
| Crustal abundance | 0.5 ppm |
| Year discovered | 1879 |
Radioactive thulium-170 is used as a portable radiation source in small X-ray devices for medical diagnostics and non-destructive materials testing in remote locations.
Frequently asked questions
Why is thulium so rarely used?
It is extremely scarce and expensive to isolate from other rare earth elements, limiting its use to highly specialized applications.
How is thulium used in anti-counterfeiting?
Thulium compounds fluoresce blue under ultraviolet light, a property utilized in Euro banknotes to prevent forgery.