Name: Thallium Symbol: Tl Atomic Number: 81 Atomic Weight: 204.383(2) Density: 11.85 g/cc Melting Point: 303.45 C Boiling Point: 1456.85 C Electron Configuration: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p1 Chemical Group: Other Metals Detailed Technical Data The data on this page is more precise and in some cases more up-to-date than the data engraved on the wooden tiles. But as always, never believe one source if the number really matters. Density, melting point and boiling point data is particularly variable and uncertain. Atomic weight data for stable elements from IUPAC 1999 Official Publication. (Uncertainty in parentheses.)