 Periodic Table 
| Thallium | Symbol | Tl alkaline-earth metal | | Atomic Number | 81 | Relative Atomic Mass 12C = 12.0000 | 204.3833 | | Atomic Radius pm | 170 | First Ionisation Energy kJ mol -1 | 589.3 | | Electronegativity | 2.17 ? | Density kg m -3 | 11850 [293 K] 11290 [l., m.p.] | | Molar Volume cm 3 | 17.24 | Thermal Conductivity W m -1 K -1 | 46.1 [300 K] | | Melting Point K | 576.7 | | Boiling Point K | 1730 | | Number of Isotopes | 41 | | Inner + outer Shells | | | Inner + outer Orbitals | | | Filling Orbital | | Ground State Electron Configuration | | | | Ground State Electron Configuration with free Orbitals (n=5) |  | | | Ground State Electron Configuration with compressed Orbitals (n=96) |  | | | | Singularity | | | | | | s | p | d | f | g | h | i | j | 1 | 2 | | | | | | | | 2 | 2 | 6 | | | | | | | 3 | 2 | 6 | 10 | | | | | | 4 | 2 | 6 | 10 | 14 | | | | | 5 | 2 | 6 | 10 | 14 | 18 | | | | 6 | 2 | 1 | 5 | 10 | 14 | 18 | 22 | | | 7 | | | | | | | | | 8 | | | | | | | | |
| | | | Term Symbol | 2P 1/2 | | Discovery | Discovered by W. Crookes (London, England) in 1861 and isolated by C.A. Maly (Paris, France) in 1862 | | Name Derived From | Greek thallos meaning 'green twig' |
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