Thulium
Definition and meaning of Thulium in chemistry.
![Thulium element card: symbol Tm, atomic number 69, atomic mass 168.93, electron configuration [Xe] 4f¹³ 6s², oxidation states +3, Lanthanide, f-block, period 6, solid at room temperature.](/assets/images/terms/thulium-chemical-element.webp)
Thulium is a chemical element with the symbol Tm and the atomic number 69. It is a bright and silvery-gray metal belonging to the lanthanide series. It is the second least common lanthanide element found naturally on our planet. The metal is soft enough that you can easily cut it with a knife.
In more detail
Mining companies mostly extract thulium from monazite and bastnasite ores found underground. It sits mixed alongside other rare earth elements in very tiny amounts. Thulium makes up only about 0.5 parts per million of the Earth's crust.
It sits near the end of the f-block on the modern periodic table. The metal behaves very much like its closest neighboring lanthanide elements. It almost always loses three electrons to form a +3 oxidation state.
The solid metal stays reasonably stable when exposed to dry atmospheric air. However, you must carefully protect it from moisture to stop it from breaking down. Thulium will burn in the air at high temperatures to form thulium(III) oxide.
The metal also dissolves very quickly when placed into a dilute acid. This acidic reaction creates a liquid solution with a pale green color. Scientists can take natural thulium-169 and place it inside a nuclear reactor.
Bombarding the atoms with neutrons creates a radioactive isotope called thulium-170. This specific radioactive isotope constantly releases a steady stream of X-rays. Thulium is extremely scarce and costs a massive amount of money to extract.
Therefore, the pure metal has very few commercial uses outside of specialized scientific research. However, it has a unique ability to emit specific colors of bright light.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Tm |
| Atomic number | 69 |
| Atomic mass | 168.93 u |
| Category | Lanthanide |
| Crustal abundance | 0.5 ppm |
| Year discovered | 1879 |
Thulium compounds glow with a bright blue light when exposed to ultraviolet rays. Governments use this special glowing property as an anti-counterfeiting feature in their paper money. The radioactive isotope thulium-170 also works as a portable radiation source in medical tools.
Frequently asked questions
Why is thulium so rarely used in everyday products?
Thulium is extremely scarce and exceptionally hard to find in the Earth's crust. It also costs a massive amount of money to separate from other rare earths. This high price strictly limits its use to a few highly specialized applications.
How is thulium used to prevent the counterfeiting of money?
Certain thulium compounds will actively fluoresce blue under an ultraviolet light source. Officials print these special compounds directly onto Euro banknotes. This hidden security feature prevents criminals from easily printing fake money.
Related terms
Sources & references
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