Discovery date : 1861
Discovered by: William Crookes
Origin of the name: Thallium is derived from the Greek 'thallos', meaning a green twig.
Allotropes : -
~>THALLIUM 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, thallium resembles tin, but discolors when exposed to air.
| FACT BOX | |||
| Group | 13 | Melting point | 304°C, 579°F, 577 K |
| Period | 6 | Boiling point | 1473°C, 2683°F, 1746 K |
| Block | p | Density (g cm−3) | 11.8 |
| Atomic number | 81 | Relative atomic mass | 204.38 |
| State at 20°C | Solid | Key isotopes | 205Tl |
| Electron configuration | [Xe] 4f145d106s26p1 | CAS number | 7440-28-0 |
| ChemSpider ID | 4514293 | ChemSpider is a free chemical structure database | |
The discovery of thallium was controversial. William Crookes of the Royal College of Science in London was the first to observe a green line in the spectrum of some impure sulfuric acid, and realised that it meant a new element. He announced his discovery in March 1861 in Chemical News. However, he did very little research into it.
Meanwhile, in 1862, Claude-August Lamy of Lille, France, began to research thallium more thoroughly and even cast a small ingot of the metal itself. The French Academy now credited him its discovery. He sent the ingot to the London International Exhibition of 1862, where it was acclaimed as a new metal and he was awarded a medal. Crookes was furious and so the exhibition committee awarded him a medal as well.