Terbium
Definition and meaning of Terbium in chemistry.
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that can be cut with a knife and is relatively stable in air compared to other lanthanides. The metal exists in two crystalline allotropes and is never found in nature as a free element.
In more detail
Terbium is typically found in minerals such as cerite, gadolinite, and monazite, and it is separated from other rare earth elements using solvent extraction. Positioned among the heavy lanthanides in the f-block of the periodic table, it is characterized by its brilliant green phosphorescence when excited by electron beams or ultraviolet light. The element is electropositive, reacting slowly with cold water and quickly with hot water to form terbium hydroxide and hydrogen gas. Terbium compounds primarily exist in the +3 oxidation state, though the +4 state is also known, particularly in terbium(IV) oxide, a dark maroon or black compound. This metal is highly valued for its role in solid-state devices and lighting phosphors, despite being one of the least abundant rare earth elements. Its magnetic properties include a ferromagnetic ordering at extremely low temperatures, transitioning to antiferromagnetic and then paramagnetic states as temperature increases.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | Tb |
| Atomic number | 65 |
| Atomic mass | 158.93 u |
| Category | Lanthanide |
| State at room temperature | Solid |
| Melting point | 1356 °C |
| Year discovered | 1843 |
Terbium oxide is used in green phosphors in fluorescent lamps and television tubes, providing the green component of the trichromatic lighting system.
Frequently asked questions
What is the primary use of terbium?
Its most significant use is in green phosphors for fluorescent lamps and displays, as well as in the alloy Terfenol-D which expands or contracts in magnetic fields.
Is terbium rare?
Yes, it is one of the rarest of the lanthanide elements, making it relatively expensive and difficult to isolate.