add site
services
publishers
database
health videos
toolbar
stats
live show
health store
more stuff
JOIN/LOGIN
| advertise add site services publishers database health videos
| | about toolbar stats live show health store more stuff JOIN/LOGIN |
Tellurium cbi.pitt.edu |
Tellurium (pronounced /t
[edit] CharacteristicsTellurium belongs to the same chemical family as oxygen, sulfur, selenium, and polonium: the chalcogen family. When crystalline, tellurium is silvery-white and when it is in pure state it has a metallic luster. It is a brittle and easily pulverized metalloid. Amorphous tellurium is found by precipitating it from a solution of tellurous or telluric acid (Te(OH)6). However, there is some debate whether this form is really amorphous or made of minute crystals. [edit] CompoundsSee also: Category:Tellurium compounds Tellurium is in the same group as sulfur and selenium and forms similar compounds. It exhibits the oxidation states −2, +2, +4, and +6, with the +4 state being most common.[2] [edit] TelluridesThe −2 oxidation state is exhibited in binary compounds with many metals, such as zinc telluride, ZnTe, formed by heating tellurium with zinc.[3] Decomposition of ZnTe with hydrochloric acid yields hydrogen telluride, H2Te, the tellurium analogue of the other chalcogen hydrides, H2O, H2S, and H2Se:
H2Te reacts with many metals to form tellurides, containing the Te2− anion.[3] Gold and silver tellurides are considered good ores. [edit] Halogen compoundsThe +2 oxidation state is exhibited by the monoxide, TeO, and the dihalides, TeCl2, TeBr2, and TeI2. The dihalides have not been obtained in pure form,[4]:274 although they are known decomposition products of the tetrahalides in organic solvents, and their derived tetrahalotellurates are well-characterized:
where X is Cl, Br, or I. These anions are square planar in geometry.[4]:281 Polynuclear anionic species also exist, such as the dark brown Te2I2−6,[4]:283 and the black Te4I2−14.[4]:285 Fluorine forms two halides with tellurium: the mixed-valence Te2F4, and TeF6. In the +6 oxidation state, the –OTeF5 structural group occurs in a number of compounds such as HOTeF5, B(OTeF5)3, Xe(OTeF5)2, Te(OTeF5)4, and Te(OTeF5)6.[5] The square antiprismic anion TeF2−8 is also attested.[6] The other halogens do not form halides with tellurium in the +6 oxidation state, but only tetrahalides (TeCl4, TeBr4, and TeI4) in the +4 state, and other lower halides (Te3Cl2, Te2Cl2, Te2Br2, Te2I, and two forms of TeI). In the +4 oxidation state, halotellurate anions are known, such as TeCl2−6 and Te2Cl2−10. Halotellurium cations are also attested, inculding TeI+3, found in TeI3AsF6.[7] [edit] Oxygen compoundsTellurium monoxide was first reported in 1883 as a black amorphous solid formed by the heat decomposition of TeSO3 in vacuum, disproportionating into tellurium dioxide, TeO2, and elemental tellurium upon heating.[8][9] Since then, however, some doubt has been cast on its existence in the solid phase, although it is known as a vapor phase fragment; the black solid may be merely an equimolar mixture of elemental tellurium and tellurium dioxide.[10] Tellurium dioxide is formed by heating tellurium in air, causing it to burn with a blue flame.[3] Tellurium trioxide, β-TeO3, is obtained by thermal decomposition of Te(OH)6. The other two forms of trioxide reported in the literature, the α- and γ- forms, were found not to be true oxides of tellurium in the +6 oxidation state, but a mixture of Te4+, OH−, and O−2.[11] Tellurium also exhibits mixed-valence oxides, Te2O5 and Te4O9.[11] The tellurium oxides and hydrated oxides form a series of acids, including tellurous acid (H2TeO3), orthotelluric acid (Te(OH)6), and metatelluric acid ((H2TeO4)n).[10] The two forms of telluric acid form tellurate salts containing the TeO2−4 and TeO6−6 anions, respectively. Tellurous acid forms tellurite salts containing the anion TeO2−3. Other tellurium cations include TeF2+8, which consists of two fused tellurium rings, and the polymeric TeF2+7. [edit] Zintl cationsWhen tellurium is treated with concentrated sulfuric acid, it forms red solutions containing the Zintl ion, Te2+4. The oxidation of tellurium by AsF5 in liquid SO2 also produces this square planar cation, as well as with the trigonal prismatic, yellow-orange Te4+6:[6]
Other tellurium Zintl cations include the polymeric Te2+7, and the blue-black Te2+8, which consists of two fused 5-membered tellurium rings. The latter cation is formed by the reaction of tellurium with tungsten hexachloride:[6]
Interchalcogen cations also exist, such as Te2Se2+6 (distorted cubic geometry) and Te2Se2+8. These are formed by oxidising mixtures of tellurium and selenium with AsF5 or SbF5.[6] [edit] Organic compoundsIn organic chemistry, tellurium forms analogues of alcohols and thiols, having the functional group –TeH, called tellurols. The –TeH functional group is also referred to with the prefix tellanyl-. [edit] IsotopesMain article: isotopes of tellurium There are 30 known isotopes of tellurium with atomic masses that range from 108 to 137. Naturally found tellurium consists of eight isotopes (listed in the main article); three of them are observed to be radioactive. 128Te has the longest known half-life, 2.2×1024 years[12], among all radioisotopes.[13] Tellurium is the lightest element known to undergo alpha decay, with isotopes 106Te to 110Te being able to undergo this mode of decay. [edit] HistoryTellurium (Latin tellus meaning "earth") was discovered in 1782 by the Hungarian Franz-Joseph Müller von Reichenstein (Müller Ferenc) in Nagyszeben (now, Sibiu) Transylvania. In 1789, another Hungarian scientist, Pál Kitaibel, also discovered the element independently, but later he gave the credit to Müller. In 1798, it was named by Martin Heinrich Klaproth who earlier isolated it from the mineral calaverite.[14] Tellurium was used as a chemical bonder in the making of the outer shell of the first atom bomb. The 1960s brought growth in thermoelectric applications for tellurium, as well as its use in free-machining steel, which became the dominant use. [edit] OccurrenceSee also: category:Telluride minerals and Telluride, Colorado  With an abundance in the Earth's crust comparable to that of platinum, tellurium is one of the rarest stable solid element in the Earth's crust. Its abundance is about 1 µg/kg.[15] By comparison, even the rarest of the lanthanides have crustal abundances of 500 µg/kg (see Abundance of elements in Earth's crust). The extreme rarity of tellurium in the Earth's crust is not a reflection of its cosmic abundance, which is in fact greater than that of rubidium, even though rubidium is ten thousand times more abundant in the Earth's crust. The extraordinarily low abundance of tellurium on Earth is because during the Earth's formation, the stable form of elements in the absence of oxygen and water was controlled by the oxidation and reduction of hydrogen. Under this scenario elements such as tellurium which form volatile hydrides were severely depleted during the formation of the Earth's crust through evaporation. Tellurium and selenium are the heavy elements mostly depleted in the Earth's crust by this process.[citation needed] Tellurium is sometimes found in its native (elemental) form, but is more often found as the tellurides of gold (calaverite, krennerite, petzite, sylvanite, and others). Tellurium compounds are the most common chemical compounds of gold found in nature (rare non-tellurides such as gold aurostibite and bismuthide are known). Tellurium is also found combined with elements other than gold, in salts of other metals. The principal source of tellurium is from anode sludges produced during the electrolytic refining of blister copper. It is a component of dusts from blast furnace refining of lead. Treatment of 500 tons of copper ore typically yields one pound (0.45 kg) of tellurium. Tellurium is produced mainly in the United States, Canada, Peru, and Japan. Commercial-grade tellurium is usually marketed as minus 200-mesh powder but is also available as slabs, ingots, sticks, or lumps. The year-end price for tellurium in 2000 was US$14 per pound. In recent years, tellurium price was driven up by increased demand and limited supply, reaching as high as US$100 per pound in 2006.[16][17] [edit] ApplicationsTellurium is a p-type semiconductor that shows a greater conductivity in certain directions which depends on atomic alignment. Chemically related to selenium and sulfur, the conductivity of this element increases slightly when exposed to light (photoconductivity). It can be doped with copper, gold, silver, tin, or other metals. When in its molten state, tellurium is corrosive to copper, iron, and stainless steel. Tellurium gives a greenish-blue flame when burned in normal air and forms tellurium dioxide as a result. Metal alloys: [18]
Other uses:
High purity metalorganics of both selenium and tellurium are used in the semiconductor industry, and are prepared by adduct purification.[19][20] Semiconductor and electronic industry uses:
[edit] PrecautionsTellurium and tellurium compounds are considered to be mildly toxic and need to be handled with care, although acute poisoning is rare.[25] Tellurium is not reported to be carcinogenic.[25] Humans exposed to as little as 0.01 mg/m3 or less in air develop "tellurium breath", which has a garlic-like odor.[26] The garlic odor that is associated with human intake of tellurium compounds is caused from the tellurium being metabolized by the body. When the body metabolizes tellurium in any oxidation state, the tellurium gets converted into dimethyl telluride, (CH3)2Te, which is volatile and is the cause of the garlic-like smell. Even though the metabolic pathways of tellurium are not known, it is generally assumed that they resemble those of the more extensively studied selenium, because the final methylated metabolic products of the two elements are similar. [edit] References
[edit] External links
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ↑ top of page ↑ | about thumbshots |
