65
  Tb  
158.925340
Terbium

Name: Terbium
Symbol: Tb
Atomic Number: 65
Atomic Weight: 158.925340
Family: Rare Earth Elements
CAS RN: 7440-27-9
Description: A silvery white metal, it is malleable, ductile, and soft.
State (25C): Solid
Oxidation states: +3

Molar Volume: 19.31 cm3/mole
Valence Electrons: 4f96s2

Boiling Point:  3296K, 3023C, 5473F
Melting Point:
1630K, 1357C, 2475F
Electrons Energy Level: 2, 8, 18, 27, 8, 2
Isotopes: 36 + 1 Stable + 18 meta states
Heat of Vaporization:  330.9 kJ/mol
Heat of Fusion: 10.8 kJ/mol
Density:  8.23g/cm3  @  300K
Specific Heat:  0.18 J/gK
Atomic Radius: 2.51
Ionic Radius: 0.923
Electronegativity: 1.2 (Pauling); 1.1 (Allrod Rochow)
57
La
138.9
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0

1s2 2s2p6 3s2p6d10 4s2p6d10f9 5s2p6 6s2

History

Terbium is fourteenth in abundance among the 17 metals usually counted as "rare-earths", present in the earth's crust to the extent of only 0.9 ppm (about 1 teaspoon in every 63 tons of earth).  Terbium was discovered in 1843 by Swedish chemist Carl Gustaf Mosander (along with erbium), 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.

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 1289C.  Small amounts of terbium are used in special lasers and some solid state devices. The monazite sand from which terbium is generally extracted contains only about 0.03% by weight of Tb.

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).

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.

Compounds

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

Isotopes

Naturally occurring terbium is composed of 1 stable isotope, 159-Tb. 36 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 24.4 hours), 154m2-Tb (t 22.7 hours) and 154m1-Tb (t 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.

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Isotope  
Atomic Mass
 
Half-Life
135Tb   0.94 ms
136Tb 135.96138 ~0.2 s
137Tb 136.95598 ~600 ms
138Tb 137.95316 ~800 ms
139Tb 138.94829 1.6 s
140Tb 139.94581 2.4 s
141Tb 140.94145 3.5 s
141mTb   7.9 s
142Tb 141.93874 597 ms
143Tb 142.93512 12 s
143mTb   <21 s
144Tb 143.93305 ~1 s
144m1Tb   4.25 s
145Tb 144.92927 ~20 min
145mTb   30.9 s
146Tb 145.92725 8 s
146m1Tb   24.1 s
147Tb 146.924045 1.64 h
147mTb   1.87 min
148Tb 147.924272 60 min
148m1Tb   2.20 min
149Tb 148.923246 4.118 h
149mTb   4.16 min
150Tb 149.923660 3.48 h
150mTb   5.8 min
151Tb 150.923103 17.609 h
151mTb   25 s
152Tb 151.92407 17.5 h
152m2Tb   4.2 min
153Tb 152.923435 2.34 d
154Tb 153.92468 21.5 h
154m1Tb   9.4 h
154m2Tb   22.7 h
155Tb 154.923505 5.32 d
156Tb 155.924747 5.35 d
156m1Tb   24.4 h
156m2Tb   5.3 h
157Tb 156.9240246 71 a
158Tb 157.9254131 180 a
158m1Tb   10.70 s
159Tb 158.9253468 STABLE
160Tb 159.9271676 72.3 d
161Tb 160.9275699 6.906 d
162Tb 161.92949 7.60 min
163Tb 162.930648 19.5 min
164Tb 163.93335 3.0 min
165Tb 164.93488 2.11 min
166Tb 165.93799 25.6 s
167Tb 166.94005 19.4 s
168Tb 167.94364 8.2 s
169Tb 168.94622 ~2 s
170Tb 169.95025 ~3 s
171Tb 170.95330 ~500 ms

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.


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Terbium Data

 

Atomic Structure

Atomic Radius: 2.51
Atomic Volume cm3/mol : 19.2cm3/mol
Covalent Radius: 1.59
Crystal Structure: Hexagonal
Ionic Radius: 0.923

Chemical Properties

Electrochemical Equivalents: 1.9765g/amp-hr
Electron Work Function: 3 eV
Electronegativity: 1.2 (Pauling); 1.1 (Allrod Rochow)
Heat of Fusion: 10.8 kJ/mol
First Ionization Potential: 5.86
Second Ionization Potential: 11.525
Third Ionization Potential: 21.91
Valence Electron Potential: 46.8 -eV
Ionization Energy (eV): 5.864 eV

Physical Properties

Atomic Mass Average: 158.9253
Boiling Point: 3296K, 3023C, 5473F
Melting Point: 1630K, 1357C, 2475F
Heat of Vaporization: 330.9 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 7E-6
Electrical Conductivity: 0.00889 106/cm
Thermal Conductivity: 0.111 W/cmK
Density: 8.23g/cm3  @  300K
Enthalpy of Atomization: 314 kJ/mole @ 25C
Enthalpy of Fusion: 10.8 kJ/mole
Enthalpy of Vaporization: 330.9 kJ/mole
Molar Volume: 19.31 cm3/mole
Specific Heat: 0.18 J/gK
Vapor Pressure: unknown
Estimated Crustal Abundance: 1.2 milligrams per kilogram
Estimated Oceanic Abundance: 1.410-7 milligrams per liter