Tellurium was discovered in 1782. It is semi-metallic in nature and present in the oxygen group of periodic table. Tellurium used as semiconductor and photosensitive material.
History and Discovery
In 1700, scientist found a new element in various ores who had both metallic and non-metallic properties. They called that element aurum paradoxum or metallum problematum, meaning problem metal [1]. Officially, it was discovered by Franz Joseph Muller von Reichenstein in 1782. He sent sample to Torbern Bergman in Uppsala, Sweden but he died. In 1798, Martin Heinrich Klaproth confirmed the existence of that element and named that new element tellurium. The word tellurium has been derived from Latin word ‘tellus’ that means ‘Earth’ [2]. In 1960, tellurium was widely used in steel alloys and thermoelectric applications.
Tellurium
| Periodic Table Classification | Group 16 Period 5 |
|---|---|
| State at 20C | Solid |
| Color | Silvery lustrous gray |
| Electron Configuration | [Kr] 4d10 5s2 5p4 |
| Electron Number | 52 |
| Proton Number | 52 |
| Electron Shell | 2, 8, 18, 18, 6 |
| Density | 6.24 g.cm-3 at 20°C |
| Atomic number | 52 |
| Atomic Mass | 127.60 g.mol -1 |
| Electronegativity according to Pauling | 2.10 |
Occurrence
Tellurium is not very common in the earth crust. Tellurium is present in about 1 part per billion in the Earth’s crust. The high atomic number and the formation of halides caused it to be lost in the space as a gas during the hot nebular formation of the planet. Like other metals such as copper, lead, silver or gold, it is often found in uncombined form but mostly present in mineral with gold. It is obtained as a by-product during the refinement of lead or copper. It is mostly found in the ores sylvanite (AgAuTe4 Silver Gold Telluride), calaverite (AuTe2 Gold Telluride) and krennerite (AuTe2 Orthorhombic gold telluride) [3]. The largest producers of tellurium are Canada, Japan and the United States.
Physical Characteristics
Tellurium is semimetallic element present in the oxygen group of the periodic table. It has two allotropes: crystalline and amorphous. Crystalline tellurium looks silvery white and have a metallic luster. Amorphous form exists in black brown powder, which is prepared by precipitating a solution of telluric acid. In molten form, tellurium is corrosive to copper, iron and stainless steel. It has high melting point about 449.51oC and boiling point is 988oC. Its chemical symbol is Te. Tellurium atomic number is 52 and atomic mass is about 127.60 g/mol.
Chemical Characteristics
Tellurium belongs to chalcogen (oxygen family). It has both properties of metal and nonmetal. When burned in air, it forms tellurium dioxide and gives a greenish blue flame. It is unaffected by water and hydrochloric acid but is dissolved in nitric acid. It is also treated with concentrated sulfuric acid. Tellurium exist in various oxidation states, -including 2, +2, +4 and +6. Reduction of tellurium metals lead to the formation of tellurides (anion Te2-) and polytellurides. The halogens forms halides in +2 and +4 states. Only fluoride forms halides in +6 oxidation sate but others form halides at +2 and +4 state. In compounds, tellurium adopts a polymeric structure consisting of zig zag chain of tellurium atoms.
Significance and Uses
- Tellurium is widely used in metallurgy (separate metals from their ores) in iron, stainless steel copper and lead alloys.
- It has high efficiencies for solar cell electric power generators.
- Tellurium is added to lead to improve its strength and resistance to corrosion.
- Tellurium is added in rubber which is helpful in curing process, less susceptible to aging and soften the normal rubber.
- Tellurium is the primary ingredient of blasting caps, explosive caps of TNT detonators etc.
- Tellurium is used as pigment for glass and ceramics.
- Bismuth telluride and lead telluride are semiconductor and used in thermoelectric devices for providing electricity or for cooling purpose.
- Tellurium is used as a catalyst for petroleum cracking, a process of converting larger hydrocarbons to smaller and simpler units, lighter hydrocarbons.
- Tellurite agar is used to identify the members of Corynebacterium (genus of bacteria, gram + and aerobic) genus.
- Tellurium is doped with gold and copper in semiconductor applications.
Health effects
In body, tellurium is partly metabolized in the form of dimethyl telluride, which has a garlic like odor. The exhalation of this gas can be indication of tellurium exposure. Prolonged exposure to tellurium may cause abdominal pain, constipation and vomiting.
Isotopes of Tellurium
Naturally occurring tellurium has eight isotopes, out of which six are stable. The stable isotopes are 120Te, 122Te, 123Te, 124Te, 125Te and 126Te. The other two are slightly radioactive 128Te and 130Te. 128Te have long half-life of 2.2 x 1024 years. Tellurium have thirty artificial radioisotopes having atomic masses ranging from 105 to 142.
REFERENCES
[1]. https://www.chemicool.com/elements/tellurium.html