Thallium, 81 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)Thallium in the periodic table Template:Infobox element/periodic table Atomic number (Z ) 81 Group Template:Infobox element/group Period period 6 Block p-block Element category Template:Infobox element/category format Electron configuration [Xe ] 4f14 5d10 6s2 6p1 Electrons per shell
2, 8, 18, 32, 18, 3 Physical properties Phase at STP solid Melting point 577 K (304 °C, 579 °F) Boiling point 1746 K (1473 °C, 2683 °F) Density (near r.t. ) 11.85 g/cm3 when liquid (at m.p. ) 11.22 g/cm3 Heat of fusion 4.14 kJ/mol [[Enthalpy of vaporization|Heat of Template:Engvar ]] 165 kJ/mol Molar heat capacity 26.32 J/(mol·K) [[Vapor pressure|Template:Engvar pressure Atomic properties Oxidation states Template:Infobox element/symbol-to-oxidation-state Electronegativity Pauling scale: 1.62 [[Ionization energy|Template:Engvar energies]] 1st: 589.4 kJ/mol 2nd: 1971 kJ/mol 3rd: 2878 kJ/mol Atomic radius empirical: 170 pm Covalent radius 145±7 pm Van der Waals radius 196 pm Template:Infobox element/spectral lines Other properties Crystal structure Template:Infobox element/crystal structure Speed of sound thin rod 818 m/s (at 20 °C) Thermal expansion 29.9 µm/(m·K) (at 25 °C) Thermal conductivity 46.1 W/(m·K) Electrical resistivity 0.18 µΩ·m (at 20 °C) Magnetic ordering diamagnetic [1] Magnetic susceptibility −50.9·10−6 cm3 /mol (298 K)[2] Young's modulus 8 GPa Shear modulus 2.8 GPa Bulk modulus 43 GPa Poisson ratio 0.45 Mohs hardness 1.2 Brinell hardness 26.5–44.7 MPa CAS Number 7440-28-0 History Naming after Greek thallos , green shoot or twig Discovery William Crookes (1861) First isolation Claude-Auguste Lamy (1862) Main isotopes of thallium Template:Infobox element/isotopes table | references
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↑ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5 ↑ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics . Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4 ↑ Dong, Z.-C.; Corbett, J. D. (1996). "Na23 K9 Tl15.3 : An Unusual Zintl Compound Containing Apparent Tl5 7− , Tl4 8− , Tl3 7− , and Tl5− Anions". Inorganic Chemistry . 35 (11): 3107–12. doi :10.1021/ic960014z . 