Terbium (Tb)

Stable Isotopes of Terbium

Isotope Z(p) N(n) Atomic Mass Natural Abundance Nuclear Spin
Tb-159  65  94  158.925343 100.00%  3/2+ 


Terbium was discovered in 1843 by Carl Mosander. It is named for the Swedish town of Ytterby.

A silvery-grey metal, terbium has a metallic luster and a hexagonal crystal structure. It is malleable, ductile, and soft enough to be cut with a knife. Its salts are colorless. It is insoluble in water and soluble in acids. In solution the metal exists only in a trivalent state. Terbium forms binary compounds with a number of elements, including hydrogen, halogens, nitrogen, phosphorus, sulfur, carbon, silicon, selenium, tellurium, boron, arsenic and antimony.

Neither terbium metal nor its salts has any important commercial use.

Properties of Terbium

Name Terbium
Symbol Tb 
Atomic number 65 
Atomic weight 158.925 
Standard state Solid at 298 ºK 
CAS Registry ID 7440-27-9 
Group in periodic table N/A 
Group name Lanthanoid 
Period in periodic table 6 (Lanthanoid) 
Block in periodic table f-block 
Color Silvery white 
Classification Metallic 
Melting point 1359 °C
Boiling point 3123 °C
Vaporization point 3221 ºC
Thermal conductivity 11.1 W/(m·K) at 298.2 ºK
Electronegativity 1.2 
Heat of vaporization 295 kJ·mol-1
Heat of fusion 10.8 kJ·mol-1
Density of liquid 7.65 g/cm3 at 1359 °C 
Density of solid 8.22 g/cm3 
Electron configuration [Xe]4f96s2 
Mean atomic radius 1.728 Å 
Ionic radii Tb3+: 0.923 Å (coordination number 6)
and 1.04 Å (coordination number 8)
Oxidation states  +3, +4 
Most common oxidation state  +3

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