Thallium was discovered independently in 1986 by William Crookes and Claude-Auguste Lamy. Due to its toxic nature, it has been historically used as ant killer and rat poison.
History and Discovery
Thallium was discovered by two chemists, Claude-Auguste Lamy and William Crookes, in 1986 who were independently working with sulfuric acid. They used flame spectroscopy for the discovery of the novel element. Thallium gave distinct green spectral lines in the spectroscopy analysis. The name thallium was given by Crookes which has been derived from the Greek word thallos which means green twig or shoot [1].
Thallium
| Periodic Table Classification | Group 13 Period 6 |
|---|---|
| State at 20C | Solid |
| Color | Silvery white |
| Electron Configuration | [Xe] 4f14 5d10 6s2 6p1 |
| Electron Number | 81 |
| Proton Number | 81 |
| Electron Shell | 2, 8, 18, 32, 18, 3 |
| Density | 11.85 g.cm-3 at 20°C |
| Atomic number | 81 |
| Atomic Mass | 204.38 g.mol -1 |
| Electronegativity according to Pauling | 1.62 |
Occurrence
Thallium is an abundant element and is present in about 0.7 mg/kg of the Earth’s crust. Thallium does not exist in free elemental form in nature. it mostly exists in the form of ores with other elements, mostly potassium. Commercially, thallium is extracted from its sulfide-ores of heavy metals, such as zinc, lead, copper etc., which contain 16% to 60 of thallium. The mineral crookesite, lorandite (TlAsS2) and hutchinsonite (TlPbAs5S9) are common minerals of thallium. It is also found in ocean beds in combination with manganese nodules. Annually, about 10 metric tons of thallium is produced worldwide as a byproduct during the smelting of lead, zinc and copper ores [2]. Large deposits of thallium are found in southern Macedonia where active mining of thallium is carried out.
Physical Characteristics
Thallium is a greyish color post-transition metal. It is soft and can be cut with a knife. Thallium is malleable. Freshly isolated thallium looks like tin and is readily discolored (becomes bluish-grey) and loses it shine when exposed to air. It is quite dense and have a density of 11.85 g/cm3. Thallium has a high boiling point, 1473 ° C and a melting point of 304 °C.
Chemical Characteristics
Thallium exists in two oxidation states, +3 and +1. Thallium compounds with +3 oxidation state are strong oxidizing agents. They are relatively unstable. Thallium reacts with halogens and thallium halides are stable in nature. thallium reacts with water to form thallium hydroxide. It dissolves in nitric acid and sulfuric acid and forms salts of nitrate and sulphate [3].
Significance and Uses
- Thallium is widely used in making various electronics, and about 70% of the thallium produced world wide is used in this industry. It is used as photoresistors, rectifiers and in gamma radiation detection devices.
- Thallium is used in glass industry.
- Thallium is used in pharmaceutical industry to make various drugs and medicines.
- Thallium is used as detectors in infrared devices.
- The radioactive isotope thallium-201 is used for nuclear medicine scan.
Health Hazards
Certain compounds of thallium are highly toxic. They have been used as insecticides and rat poison. However, due to the dangers of their non-selective poisoning, the use of thallium-based poisons has been banned in various countries. Thallium compounds are highly soluble in water that increases their risk of toxicity. Thallium contamination of the environment has been reported to be caused by coal-burning power plants, emission from cement factories and water contamination by leaching of thallium from ore processing plants. These can be readily absorbed through the skin. Thallium is a potential human carcinogens [4].
Isotopes of Thallium
There are twenty-five isotopes of thallium. Their atomic masses range from 184 to 210. Naturally occurring thallium have two stable isotopes, thalium-203 and thalium-205. These two isotopes make all naturally occurring thallium. Among the radioactive isotopes, thallium-204 is the most stable isotope and have a half-life of 3.78 years [5].
REFERENCES
[1]. Liddell, Henry George and Scott, Robert (eds.) “θαλλος Archived 2016-04-15 at the Wayback Machine.”, in A Greek–English Lexicon, Oxford University Press
[2]. Guberman, David E. “Mineral Commodity Summaries 2010: Thallium” (PDF). United States Geological Survey. Retrieved 2010-05-13
[3]. Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils (1985). “Thallium”. Lehrbuch der Anorganischen Chemie (in German) (91–100 ed.). Walter de Gruyter. pp. 892–893. ISBN 3-11-007511-3.
[4]. “Biology of Thallium”. webelemnts. Retrieved 2008-11-11.
[5]. Audi, Georges; Bersillon, O.; Blachot, J.; Wapstra, A. H. (2003). “The NUBASE Evaluation of Nuclear and Decay Properties”. Nuclear Physics A. Atomic Mass Data Center. 729 (1): 3–128. Bibcode:2003NuPhA.729….3A. doi:10.1016/j.nuclphysa.2003.11.001