Terbium

Vapor pressure
65	gadolinium ← terbium → dysprosium
	periodic table
General
Name, Symbol, Number	terbium, Tb, 65
Chemical series	lanthanides
Group, Period, Block	n/a, 6, f
Appearance	silvery white ;
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/cm³
Liquid density at m.p.	7.65 g/cm³
Melting point	1629 K; (1356 °C, 2473 °F)
Boiling point	3503 K; (3230 °C, 5846 °F)
Heat of fusion	10.15 kJ/mol
Heat of vaporization	293 kJ/mol
Heat capacity	(25 °C) 28.91 J/(mol·K)
Atomic properties
Crystal structure	hexagonal
Oxidation states	3, 4; (weakly basic oxide)
Electronegativity	? 1.2 (Pauling scale)
Ionization energies; (more)	1st: 565.8 kJ/mol
	2nd: 1110 kJ/mol
	3rd: 2114 kJ/mol
Atomic radius	175 pm
Atomic radius (calc.)	225 pm
Miscellaneous
Magnetic ordering	ferromagnetic; in dry ice [1]
Electrical resistivity	(r.t.) (α, poly); 1.150 µΩ·m
Thermal conductivity	(300 K) 11.1 W/(m·K)
Thermal expansion	(r.t.) (α, poly); 10.3 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 2620 m/s
Speed of sound (thin rod)	(r.t.) (α form) 55.7 m/s
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
Notable isotopes

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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 color 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

See also terbium compounds.

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 (t_½ 24.4 hours), 154m2-Tb (t_½ 22.7 hours) and 154m1-Tb (t_½ 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.

References
ISBN links support NWE through referral fees

Los Alamos National Laboratory – Terbium

External links

Wikimedia Commons has media related to::

Terbium

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