Lanthanum, 57 General properties Pronunciation Template:Infobox element/pronunciation Appearance silvery white Standard atomic weight (A r, standard ) Template:Infobox element/standard atomic weight Mass number Template:Infobox element/symbol-to-most-stable-isotope (most stable isotope)Lanthanum in the periodic table Template:Infobox element/periodic table Atomic number (Z ) 57 Group Template:Infobox element/group Period period 6 Block d-block Element category Template:Infobox element/category format , sometimes considered a transition metal Electron configuration [Xe ] 5d1 6s2 Electrons per shell
2, 8, 18, 18, 9, 2 Physical properties Phase at STP solid Melting point 1193 K (920 °C, 1688 °F) Boiling point 3737 K (3464 °C, 6267 °F) Density (near r.t. ) 6.162 g/cm3 when liquid (at m.p. ) 5.94 g/cm3 Heat of fusion 6.20 kJ/mol [[Enthalpy of vaporization|Heat of Template:Engvar ]] 400 kJ/mol Molar heat capacity 27.11 J/(mol·K) [[Vapor pressure|Template:Engvar pressure Atomic properties Oxidation states Template:Infobox element/symbol-to-oxidation-state Electronegativity Pauling scale: 1.10 [[Ionization energy|Template:Engvar energies]] 1st: 538.1 kJ/mol 2nd: 1067 kJ/mol 3rd: 1850.3 kJ/mol Atomic radius empirical: 187 pm Covalent radius 207±8 pm Template:Infobox element/spectral lines Other properties Crystal structure Template:Infobox element/crystal structure Speed of sound thin rod 2475 m/s (at 20 °C) Thermal expansion α, poly: 12.1 µm/(m·K) (at r.t. ) Thermal conductivity 13.4 W/(m·K) Electrical resistivity α, poly: 615 nΩ·m (at r.t. ) Magnetic ordering paramagnetic [1] Magnetic susceptibility +118.0·10−6 cm3 /mol (298 K)[2] Young's modulus α form: 36.6 GPa Shear modulus α form: 14.3 GPa Bulk modulus α form: 27.9 GPa Poisson ratio α form: 0.280 Mohs hardness 2.5 Vickers hardness 360–1750 MPa Brinell hardness 350–400 MPa CAS Number 7439-91-0 History Discovery Carl Gustaf Mosander (1838) Main isotopes of lanthanum Template:Infobox element/isotopes table | references
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