2007 Schools Wikipedia Selection. Related subjects: Chemical elements

65 gadoliniumterbiumdysprosium


Periodic Table - Extended Periodic Table
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·cm−3
Liquid density at m.p. 7.65 g·cm−3
Melting point 1629  K
(1356 ° C, 2473 ° F)
Boiling point 3503 K
(3230 ° C, 5846 ° F)
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
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1789 1979 (2201) (2505) (2913) (3491)
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−1
2nd: 1110 kJ·mol−1
3rd: 2114 kJ·mol−1
Atomic radius 175 pm
Atomic radius (calc.) 225 pm
Magnetic ordering ferromagnetic
in dry ice
Electrical resistivity ( r.t.) (α, poly)
1.150 µΩ·m
Thermal conductivity (300 K) 11.1 W·m−1·K−1
Thermal expansion ( r.t.) (α, poly)
10.3 µm/(m·K)
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
Main article: Isotopes of terbium
iso NA half-life DM DE ( MeV) DP
157Tb syn 71 y ε 0.060 157Gd
158Tb syn 180 y ε 1.220 158Gd
β- 0.937 158Dy
159Tb 100% Tb is stable with 94 neutrons

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.


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.


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.


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).


Terbium compounds include:

  • Fluorides
    • TbF3
    • TbF4
  • Chlorides
    • TbCl3
  • Bromides
    • TbBr3
  • Iodides
    • TbI3
  • Oxides
    • Tb2O3
    • Tb4O7
  • Sulfides
    • Tb2S3
  • Nitrides
    • TbN


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.


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.

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