69

Thulium Atomic number 69 Group, block group n/a, f-block Period period 6 Element category lanthanide Standard atomic weight (±) (Ar) 168.93422(2)1 Electron configuration Xe 4f13 6s2 per shell 2, 8, 18, 31, 8, 2 Physical properties Phase solid Melting point 1818 K (1545 °C, 2813 °F) Boiling point 2223 K (1950 °C, 3542 °F) Density near r.t. 9.32 g/cm3 when liquid, at m.p. 8.56 g/cm3 Heat of fusion 16.84 kJ/mol Heat of vaporization 191 kJ/mol Molar heat capacity 27.03 J/(mol·K) vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1117 1235 1381 1570 (1821) (2217) Atomic properties Oxidation states 2, 3 (a basic oxide) Electronegativity Pauling scale: 1.25 Ionization energies 1st: 596.7 kJ/mol 2nd: 1160 kJ/mol 3rd: 2285 kJ/mol Atomic radius empirical: 176 pm Covalent radius 190±10 pm Miscellanea Crystal structure hexagonal close-packed (hcp) Hexagonal close packed crystal structure for thulium Thermal expansion poly: 13.3 µm/(m·K) (at r.t.) Thermal conductivity 16.9 W/(m·K) Electrical resistivity poly: 676 nΩ·m (at r.t.) Magnetic ordering paramagnetic (at 300 K) Young's modulus 74.0 GPa Shear modulus 30.5 GPa Bulk modulus 44.5 GPa Poisson ratio 0.213 Vickers hardness 470–650 MPa Brinell hardness 470–900 MPa CAS Number 7440-30-4 History Naming after Thule, a mythical region in Scandinavia Discovery and first isolation Per Teodor Cleve (1879)