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81Tl204.380
Thallium
Post-Transition MetalThallium is a chemical element with symbol Tl and atomic number 81. This soft gray post-transition metal is not found free in nature. When isolated, it resembles tin, but discolors when exposed to air.
Phase: SolidAppearance: silvery white
2, 8, 18, 32, 18, 3
Physical Properties
Atomic Mass204.38 u
Density11.85 g/cm³
Melting Point577 K
Boiling Point1746 K
Molar Heat26.32 J/(mol·K)
Period6
PhaseSolid
Chemical Properties
Electron Configuration1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p1
Semantic Config[Xe] 4f14 5d10 6s2 6p1
Shells2, 8, 18, 32, 18, 3
Electron Affinity36.4 kJ/mol
Electronegativity1.62
Ionization Energies
IE1: 589.4 kJ/molIE2: 1971 kJ/molIE3: 2878 kJ/mol
Discovery
Discovered byWilliam Crookes