Thallium comes from Greek-thallos meaning “a green shoot or twig”<ref>Liddell, Henry George and Scott, Robert (eds.) "θαλλος", in A Greek–English Lexicon, Oxford University Press.</ref> since Thallium has bright green spectral emission lines.<ref>Gagnon, S. (n.d.). It's Elemental - The Element Thallium. Retrieved from http://education.jlab.org/itselemental/ele081.html</ref> It is the 81th element with the symbol Tl in the periodic table. Thallium can be found in group 13 and period 6. It is a post-transition metal which can't be found free in nature. Thallium can be seen as a metallic luster, but then develops into a blueish-grey color resembling lead's appearance.<ref>Lenntech, B. (n.d.). Thallium (Tl) - Chemical properties, Health and Environmental effects. Retrieved from http://www.lenntech.com/periodic/elements/tl.htm</ref>
|Atomic Weight||204.38 amu.|
|Melting Point ( °C )||577 K|
|Boiling Point ( °C )||1746 K|
|Density (g/cm3)||11.85 g/cm3|
|Earth crust (%)||2.6 log|
|Electron configuration||[Xe] 4f14 5d106s2 6p1|
|Ionization energy (eV)||589.139 kJ/mol|
Chemists William Crooks and Claude-Auguste Lamy discovered Thallium in 1861. They had used the newly developed Flame Spectroscopy Method where Thallium produced a green spectral line. <ref>Weeks, Mary Elvira (1932). "The discovery of the elements. XIII. Supplementary note on the discovery of thallium". Journal of Chemical Education 9 (12): 2078. Bibcode:1932JChEd...9.2078W. doi:10.1021/ed009p2078.</ref> At first, Crooks used this method to make spectroscopic determinations to see any signs of tellurium in the selenium from a sludge he had obtain. Instead of seeing the yellow spectral lines that tellurium produce, he discovered a bright green spectral line no one has seen before. He then named it thallium after the greek word thallos meaning green twig.
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