Thallium is element 81, a post-transition of the p block, in group 13, period 6. Its ground-state configuration is [Xe] 4f14 5d10 6s2 6p1, and it usually shows the oxidation states 0, 1, 3.
It was discovered in 1861, by Crookes.
Name origin: the Greek thallos, 'green twig'.
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