Terbium
Pronunciation/ˈtɜːrbiəm/ (TUR-bee-əm)
Appearancesilvery white
Standard atomic weight Ar, std(Tb)158.925354(8)
Atomic number (Z)65
Groupgroup n/a
Periodperiod 6
Blockf-block
Element category  Lanthanide
Electron configuration[Xe] 4f9 6s2
Electrons per shell
2, 8, 18, 27, 8, 2
Phase at STPsolid
Melting point1629 K ​(1356 °C, ​2473 °F)
Boiling point3396 K ​(3123 °C, ​5653 °F)
Density (near r.t.)8.23 g/cm3
when liquid (at m.p.)7.65 g/cm3
Heat of fusion10.15 kJ/mol
Heat of vaporization391 kJ/mol
Molar heat capacity28.91 J/(mol·K)
Oxidation states0, +1, +2, +3, +4 (a weakly basic oxide)
ElectronegativityPauling scale: 1.2 (?)
Ionization energies
  • 1st: 565.8 kJ/mol
  • 2nd: 1110 kJ/mol
  • 3rd: 2114 kJ/mol
Atomic radiusempirical: 177 pm
Covalent radius194±5 pm
Natural occurrenceprimordial
Speed of sound thin rod2620 m/s (at 20 °C)
Thermal expansionat r.t. α, poly: 10.3 µm/(m·K)
Thermal conductivity11.1 W/(m·K)
Electrical resistivityα, poly: 1.150 µΩ·m (at r.t.)
Magnetic orderingparamagnetic at 300 K
Magnetic susceptibility+146,000·10−6 cm3/mol (273 K)
Young's modulusα form: 55.7 GPa
Shear modulusα form: 22.1 GPa
Bulk modulusα form: 38.7 GPa
Poisson ratioα form: 0.261
Vickers hardness450–865 MPa
Brinell hardness675–1200 MPa
CAS Number7440-27-9
Namingafter Ytterby (Sweden), where it was mined
Discovery and first isolationCarl Gustaf Mosander (1843)