Terbium
2007 Schools Wikipedia Selection. Related subjects: Chemical elements
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| General | ||||||||||||||||||||||||||||
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| Name, Symbol, Number | terbium, Tb, 65 | |||||||||||||||||||||||||||
| Chemical series | lanthanides | |||||||||||||||||||||||||||
| Group, Period, Block | n/a, 6, f | |||||||||||||||||||||||||||
| Appearance | silvery white |
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| Atomic mass | 158.92535 (2) g/mol | |||||||||||||||||||||||||||
| Electron configuration | [Xe] 4f9 6s2 | |||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 18, 27, 8, 2 | |||||||||||||||||||||||||||
| Physical properties | ||||||||||||||||||||||||||||
| Phase | solid | |||||||||||||||||||||||||||
| Density (near r.t.) | 8.23 g·cm−3 | |||||||||||||||||||||||||||
| Liquid density at m.p. | 7.65 g·cm−3 | |||||||||||||||||||||||||||
| Melting point | 1629 K (1356 ° C, 2473 ° F) |
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| Boiling point | 3503 K (3230 ° C, 5846 ° F) |
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| Heat of fusion | 10.15 kJ·mol−1 | |||||||||||||||||||||||||||
| Heat of vaporization | 293 kJ·mol−1 | |||||||||||||||||||||||||||
| Heat capacity | (25 °C) 28.91 J·mol−1·K−1 | |||||||||||||||||||||||||||
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| Atomic properties | ||||||||||||||||||||||||||||
| Crystal structure | hexagonal | |||||||||||||||||||||||||||
| Oxidation states | 3, 4 (weakly basic oxide) |
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| Electronegativity | ? 1.2 (Pauling scale) | |||||||||||||||||||||||||||
| Ionization energies ( more) |
1st: 565.8 kJ·mol−1 | |||||||||||||||||||||||||||
| 2nd: 1110 kJ·mol−1 | ||||||||||||||||||||||||||||
| 3rd: 2114 kJ·mol−1 | ||||||||||||||||||||||||||||
| Atomic radius | 175 pm | |||||||||||||||||||||||||||
| Atomic radius (calc.) | 225 pm | |||||||||||||||||||||||||||
| Miscellaneous | ||||||||||||||||||||||||||||
| Magnetic ordering | ferromagnetic in dry ice |
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| Electrical resistivity | ( r.t.) (α, poly) 1.150 µΩ·m |
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| Thermal conductivity | (300 K) 11.1 W·m−1·K−1 | |||||||||||||||||||||||||||
| Thermal expansion | ( r.t.) (α, poly) 10.3 µm/(m·K) |
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| Speed of sound (thin rod) | (20 °C) 2620 m/s | |||||||||||||||||||||||||||
| Young's modulus | (α form) 55.7 GPa | |||||||||||||||||||||||||||
| Shear modulus | (α form) 22.1 GPa | |||||||||||||||||||||||||||
| Bulk modulus | (α form) 38.7 GPa | |||||||||||||||||||||||||||
| Poisson ratio | (α form) 0.261 | |||||||||||||||||||||||||||
| Vickers hardness | 863 MPa | |||||||||||||||||||||||||||
| Brinell hardness | 677 MPa | |||||||||||||||||||||||||||
| CAS registry number | 7440-27-9 | |||||||||||||||||||||||||||
| Selected isotopes | ||||||||||||||||||||||||||||
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| References | ||||||||||||||||||||||||||||
Terbium ( IPA: /ˈtɛː(r)biəm/) is a chemical element in the periodic table that has the symbol Tb and atomic number 65.
Notable characteristics
Terbium is a silvery-white rare earth metal that is malleable, ductile and soft enough to be cut with a knife. It is reasonably stable in air, and two crystal allotropes exist, with a transformation temperature of 1289 °C.
Applications
Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate, materials that are used in solid-state devices, and as a crystal stabilizer of fuel cells which operate at elevated temperatures, together with ZrO2. Terbium is also used in alloys and in the production of electronic devices, its oxide is used in green phosphors in fluorescent lamps and colour TV tubes. Sodium terbium borate is used in solid state devices.
History
Terbium was discovered in 1843 by Swedish chemist Carl Gustaf Mosander, who detected it as an impurity in Yttrium-oxide, Y2O3, and named after the village Ytterby in Sweden. It was not isolated in pure form until the recent advent of ion exchange techniques.
Terbium is classified as a rare earth element. The term "rare" is misleading because terbium is more common than metals such as silver and mercury. The name "rare earth" meant something else to early chemists. It was used because the rare earth elements were very difficult to separate from each other. They were not "rare" in the Earth, but they were "rarely" used for anything.
Occurrence
Terbium is never found in nature as the free element, but it is contained in many minerals, including cerite, gadolinite, monazite ((Ce,LaTh,Nd,Y)PO4, which contains up to 0.03% of terbium), xenotime (YPO4) and euxenite ((Y,Ca,Er,La,Ce,U,Th)(Nb,Ta,Ti)2O6, which contains 1% or more of terbium).
Compounds
Terbium compounds include:
- Fluorides
- TbF3
- TbF4
- Chlorides
- TbCl3
- Bromides
- TbBr3
- Iodides
- TbI3
- Oxides
- Tb2O3
- Tb4O7
- Sulfides
- Tb2S3
- Nitrides
- TbN
Isotopes
Naturally occurring terbium is composed of 1 stable isotope, 159-Tb. 33 radioisotopes have been characterized, with the most stable being 158-Tb with a half-life of 180 years, 157-Tb with a half-life of 71 years, and 160-Tb with a half-life of 72.3 days. All of the remaining radioactive isotopes have half-lifes that are less than 6.907 days, and the majority of these have half lifes that are less than 24 seconds. This element also has 18 meta states, with the most stable being 156m1-Tb (t½ 24.4 hours), 154m2-Tb (t½ 22.7 hours) and 154m1-Tb (t½ 9.4 hours).
The primary decay mode before the most abundant stable isotope, 159-Tb, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 159-Tb are element Gd (gadolinium) isotopes, and the primary products after are element Dy (dysprosium) isotopes.
Precautions
As with the other lanthanides, terbium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail. Terbium has no known biological role.