Tellurium,Iodine,Xenon

Tellurium is a chemical element that has the symbol Te and atomic number 52. A brittle, mildly toxic, rare, silver-white metalloid which looks similar to tin, tellurium is chemically related toselenium and sulfur. It is occasionally found in native form, as elemental crystals. Tellurium is far more common in the universe than on Earth.Sony VAIO VGN-SZ58GN/C Battery

Its extreme rarity in the Earth's crust, comparable to that of platinum, is partly due to its high atomic number, but also due to its formation of a volatile hydride which caused the element to be lost to space as a gas during the hot nebular formation of the planet.Sony VAIO VGN-SZ58N Battery

Tellurium was discovered in Transylvania (today part of Romania) in 1782 by Franz-Joseph Müller von Reichenstein in a mineral containing tellurium and gold. Martin Heinrich Klaproth named the new element in 1798 after the Latin word for "earth", tellus. Gold telluride minerals (responsible for the name of Telluride, Colorado) are the most notable natural gold compounds.Sony VAIO VGN-SZ61MN/B Battery

However, they are not a commercially significant source of tellurium itself, which is normally extracted as by-product of copper and lead production.

Tellurium is commercially primarily used in alloys, foremost in steel and copper to improve machinability. Applications in solar panels and as a semiconductor material also consume a considerable fraction of tellurium production.Sony VAIO VGN-SZ61VN/X Battery

Tellurium has no biological function, although fungi can incorporate it in place of sulfur and selenium into amino acidssuch as telluro-cysteine and telluro-methionine.^[3] In humans, tellurium is partly metabolized into dimethyl telluride, (CH₃)₂Te, a gas with a garlic-like odor which is exhaled in the breath of victims of tellurium toxicity or exposure.Sony VAIO VGN-SZ61WN/C Battery

Physical properties

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 telluricacid (Te(OH)₆).Sony VAIO VGN-SZ640N/B Battery

ellurium is a semiconductor that shows a greater electrical conductivity in certain directions which depends on atomic alignment; the conductivity increases slightly when exposed to light (photoconductivity).^[5] When in its molten state, tellurium is corrosive to copper, iron and stainless steel.Sony VAIO VGN-SZ645P3 Battery

Chemical properties

Tellurium adopts a polymeric structure, consisting of zig-zag chains of Te atoms. This gray material resists oxidation by air and is nonvolatile.

Naturally occurring tellurium has eight isotopes. Four of those isotopes, ¹²²Te, ¹²⁴Te, ¹²⁵Te and ¹²⁶Te, are stable.Sony VAIO VGN-SZ650N/C Battery

The other four, ¹²⁰Te, ¹²³Te, ¹²⁸Te and ¹³⁰Te, have been observed to be radioactive.^[6][7] The stable isotopes make up only 33.2 % of the naturally occurring tellurium; this is possible due to the long half-lives of the unstable isotopes. They are in the range from 10¹³ to 2.2 10²⁴ years (for ¹²⁸Te).Sony VAIO VGN-SZ660N/C Battery

This makes ¹²⁸Te the isotope with the longest half life among allradionuclides.,^[8] which is approximately 160 trillion (10¹²) times the age of known universe.

There are 38 known nuclear isomers of tellurium with atomic masses that range from 105 to 142.Sony VAIO VGN-SZ670N/C Battery

Tellurium is among the lightest elements known to undergo alpha decay, with isotopes ¹⁰⁶Te to ¹¹⁰Te being able to undergo this mode of decay.^[6]The atomic mass of tellurium (127.60 g·mol^?1) exceeds that of the following element iodine (126.90 g·mol^?1).Sony VAIO VGN-SZ680ND Battery

Occurrence

With an abundance in the Earth's crust comparable to that of platinum, tellurium is one of the rarest stable solid elements in the Earth's crust. Its abundance is about 1 µg/kg.^[10] In comparison, even the rarest of the lanthanides have crustal abundances of 500 µg/kg (see Abundance of the chemical elements).Sony VAIO VGN-SZ691N/X Battery

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 rather thought to be due to conditions in the Earth's formation,Sony VAIO VGN-SZ71E/B Battery

when the stable form of certain elements, in the absence of oxygen andwater, was controlled by the reductive power of free hydrogen. Under this scenario, certain elements such as tellurium which form volatile hydrides were severely depleted during the formation of the Earth's crust, through evaporation of these hydrides.Sony VAIO VGN-SZ71VN/X Battery

Tellurium and selenium are the heavy elements most depleted in the Earth's crust by this process.

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).Sony VAIO VGN-SZ71WN/C Battery

Tellurium is also found combined with elements other than gold, in salts of other metals. In contrast to selenium, tellurium is not able to replace sulfur in its minerals. This is due to the large difference in ion radius of sulfur and tellurium. In consequence, many sulfide minerals contain considerable amounts of selenium, but only traces of tellurium.Sony VAIO VGN-SZ74B/B Battery

In the gold rush of 1893, diggers in Kalgoorlie discarded a pyritic material which got in their way as they searched for pure gold. The Kalgoorlie waste was thus used to fill in potholes or as part of sidewalks. Three years passed before it was realized that this waste was calaverite, a telluride of gold that had not been recognized. This led to a second gold rush in 1896 which included mining the streets.Sony VAIO VGN-SZ750N/C Battery

Production

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.Sony VAIO VGN-SZ75B/B Battery

Tellurium is produced mainly in the United States, Peru, Japan and Canada.^[14] For the year 2006 the British Geological Survey gives the following numbers: United States 50 t, Peru 37 t, Japan 24 t and Canada 11 t.^[15]

The anode sludges contain the selenides and tellurides of the noble metals in compounds with the formula M₂Se or M₂Te (M = Cu, Ag, Au).Sony VAIO VGN-SZ76 Battery

At temperatures of 500 °C the anode sludges are roasted with sodium carbonate under air. The metal ions are reduced to the metals, while the telluride is converted to sodium tellurite.

M₂Te + O₂ + Na₂CO₃ ? Na₂TeO₃ + 2 M + CO₂

Tellurites can be leached from the mixture with water and are normally present as hydrotellurites HTeO₃^– in solution.Sony VAIO VGN-SZ770N/C Battery

Selenites are also formed during this process, but they can be separated by adding sulfuric acid. The hydrotellurites are converted into the insoluble tellurium dioxide while the selenites stay in solution.

HTeO₃^– + OH^– + H₂SO₄ ? TeO₂ + 2 SO₄^2? + 2 H₂O

The reduction to the metal is done either by electrolysis or by reacting the tellurium dioxide with sulfur dioxide in sulfuric acid.Sony VAIO VGN-SZ77N Battery

TeO₂ + 2 SO₂ + 2H₂O ? Te + SO₄^2? + 4 H⁺

Commercial-grade tellurium is usually marketed as 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, the tellurium price was driven up by increased demand and limited supply, reaching as high as US$100 per pound in 2006.Sony VAIO VGN-SZ780 Battery

Despite an expected doubling in production due to improved extraction methods, the United States Department of Energy (DoE) anticipates a supply shortfall of tellurium by 2025.

Compounds

Tellurium belongs to the same chemical family as oxygen, sulfur, selenium and polonium: the chalcogen family. Tellurium and selenium compounds are similar.Sony VAIO VGN-SZ78N Battery

It exhibits the oxidation states ?2, +2, +4 and +6, with the +4 state being most common.

Tellurides

Reduction of Te metal produces the tellurides and polytellurides, Te_n^2–. The ?2 oxidation state is exhibited in binary compounds with many metals, such as zinc telluride, ZnTe, formed by heating tellurium with zinc.Sony VAIO VGN-SZ791N/X Battery

Decomposition of ZnTe with hydrochloric acid yields hydrogen telluride (H₂Te), a highly unstable analogue of the other chalcogen hydrides, H₂O, H₂S and H₂Se:

ZnTe + 2 HCl ? ZnCl₂ + H₂Te

H₂Te is unstable, whereas salts of its conjugate base [TeH]^– are stable.Sony VAIO VGN-SZ84NS Battery

Halides

The +2 oxidation state is exhibited by the dihalides, TeCl₂, TeBr₂ and TeI₂. The dihalides have not been obtained in pure form, although they are known decomposition products of the tetrahalides in organic solvents, and their derived tetrahalotellurates are well-characterized:Sony VAIO VGN-SZ84PS Battery

Te + X₂ + 2 X^? ? TeX2?4

where X is Cl, Br, or I. These anions are square planar in geometry. Polynuclear anionic species also exist, such as the dark brown Te₂I2?6,^[21]:283 and the black Te₄I2?14.^[21]:285Sony VAIO VGN-SZ84S Battery

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.^[22] The square antiprismatic anion TeF2?8 is also attested.Sony VAIO VGN-SZ84US Battery

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, including TeI+3, found in TeI₃AsF₆.Sony VAIO VGN-SZ85NS Battery

Oxocompounds

Tellurium 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.Sony VAIO VGN-SZ85S Battery

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.

Tellurium dioxide is formed by heating tellurium in air, causing it to burn with a blue flame.Sony VAIO VGN-SZ85US Battery

Tellurium trioxide, ?-TeO₃, is obtained by thermal decomposition of Te(OH)₆. The other two forms of trioxide reported in the literature, the ?- and ?- forms, were found not to be true oxides of tellurium in the +6 oxidation state, but a mixture of Te⁴⁺, OH^? and O?2. Tellurium also exhibits mixed-valence oxides, Te₂O₅ and Te₄O₉.Sony VAIO VGN-SZ94NS Battery

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).^[26] The two forms of telluric acid form tellurate salts containing the TeO2–4 and TeO6?6 anions, respectively.Sony VAIO VGN-SZ94PS Battery

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.

Zintl cations

When tellurium is treated with concentrated sulfuric acid, it forms red solutions containing the Zintl ion, Te2+4.Sony VAIO VGN-SZ94S Battery

The oxidation of tellurium by AsF₅ in liquid SO₂also produces this square planar cation, as well as with the trigonal prismatic, yellow-orange Te4+6:4 Te + 3 AsF₅ ? Te2+4(AsF?6)₂ + AsF₃6 Te + 6 AsF₅ ? Te4+6(AsF?6)₄ + 2 AsF₃ 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:Sony VAIO VGN-SZ94US Battery

8 Te + 2 WCl₆ ? Te2+8(WCl?6)₂

Interchalcogen cations also exist, such as Te₂Se2+6 (distorted cubic geometry) and Te₂Se2+8. These are formed by oxidizing mixtures of tellurium and selenium with AsF₅or SbF₅.Sony VAIO VGN-SZ95NS Battery

Organotellurium compounds

Tellurium does not readily form analogues of alcohols and thiols, with the functional group –TeH and are called tellurols. The –TeH functional group is also attributed to using the prefix tellanyl-.Like H₂Te, these species are unstable with respect to loss of hydrogen. Telluraethers (R-Te-R) are more stable as aretelluroxides.Sony VAIO VGN-SZ95S Battery

Tellurium (Latin tellus meaning "earth") was discovered in the 18th century in a gold ore from the mines in Zlatna, near what is now Sibiu, Transylvania. This ore was known as "Faczebajer weißes blättriges Golderz" (white leafy gold ore from Faczebaja) orantimonalischer Goldkies (antimonic gold pyrite), and, according to Anton von Rupprecht, was Spießglaskönig (argent molybdique), containing native antimony.Sony VAIO VGN-SZ95US Battery

In 1782 Franz-Joseph Müller von Reichenstein, who was then serving as the Austrian chief inspector of mines in Transylvania, concluded that the ore did not contain antimony, but that it was bismuth sulfide. The following year, he reported that this was erroneous and that the ore contained mostly gold and an unknown metal very similar to antimony.Sony VAIO VGN-TZ121 Battery

After a thorough investigation which lasted for three years and consisted of more than fifty tests, Müller determined the specific gravity of the mineral and noted the radish-like odor of the white smoke which passed off when the new metal was heated, the red color which the metal imparts to sulfuric acid, and the black precipitate which this solution gives when diluted with water.Sony VAIO VGN-TZ13 Battery

Nevertheless, he was not able to identify this metal and gave it the names aurum paradoxium and metallum problematicum, as it did not show the properties predicted for the expected antimony.

In 1789, another Hungarian scientist, Pál Kitaibel, also discovered the element independently in an ore from Deutsch-Pilsen which had been regarded as argentiferous molybdenite, but later he gave the credit to Müller.Sony VAIO VGN-TZ130N/B Battery

In 1798, it was named by Martin Heinrich Klaproth who earlier isolated it from the mineral calaverite. The 1960s brought growth in thermoelectric applications for tellurium (as bismuth telluride), as well as its use in free-machining steel, which became the dominant use.Sony VAIO VGN-TZ131 Battery

Metallurgy

The largest consumer of tellurium is metallurgy, where it is used in iron, copper and lead alloys. When added to stainless steel and copper it makes these metals more machinable. It is alloyed into cast iron for promoting chill for spectroscopic purposes, as the presence of electrically conductive free graphite tends to deleteriously affect spark emission testing results.Sony VAIO VGN-TZ132/N Battery

In lead it improves strength and durability and decreases the corrosive action of sulfuric acid.

Semiconductor and electronic industry uses

Tellurium is used in cadmium telluride (CdTe) solar panels. National Renewable Energy Laboratory lab tests using this material achieved some of the highest efficiencies for solar cell electric power generation.Sony VAIO VGN-TZ132N Battery

Massive commercial production of CdTe solar panels by First Solar in recent years has significantly increased tellurium demand. If some of the cadmium in CdTe is replaced by zinc then (Cd,Zn)Te is formed which is used in solid-state X-ray detectors.

Alloyed with both cadmium and mercury, to form mercury cadmium telluride, an infrared sensitive semiconductor material is formed.Sony VAIO VGN-TZ150N/B Battery

Organotellurium compounds such as dimethyl telluride, diethyl telluride, diisopropyl telluride, diallyl telluride andmethyl allyl telluride are used as precursors for metalorganic vapor phase epitaxy growth of II-VI compound semiconductors. Diisopropyl telluride (DIPTe) is employed as the preferred precursor for achieving the low-temperature growth of CdHgTe byMOVPE.Sony VAIO VGN-TZ150N/N Battery

For these processes highest purity metalorganics of both selenium and tellurium are used. The compounds for semiconductor industry and are prepared by adduct purification.

Tellurium as a tellurium suboxide is used in the media layer of several types of rewritable optical discs, including ReWritable Compact Discs (CD-RW), ReWritable Digital Video Discs (DVD-RW) and ReWritable Blu-ray Discs.Sony VAIO VGN-TZ160CB Battery

Tellurium is used in the new phase change memory chips.^[49] developed by Intel.^[50] Bismuth telluride (Bi₂Te₃) and lead telluride are working elements ofthermoelectric devices. Lead telluride is used in far-infrared detectors.

Other uses

• Used to color ceramics.Sony VAIO VGN-TZ160N/B Battery

• The strong increase in optical refraction upon the addition of selenides and tellurides into glass is used in the production of glass fibers for telecommunications. These chalcogenide glasses are widely used.


• Mixtures of selenium and tellurium are used with barium peroxide as oxidizer in the delay powder of electric blasting caps.Sony VAIO VGN-TZ16GN/B Battery

• Organic tellurides have been employed as initiators for living radical polymerization and electron-rich mono- and di-tellurides possess antioxidant activity.


• Rubber can be vulcanized with tellurium instead of sulfur or selenium. The rubber produced in this way shows improved heat resistance.Sony VAIO VGN-TZ16N Battery

• Tellurite agar is used to identify member of the corynebacterium genus, most typically Corynebacterium diphtheriae, the pathogen responsible for diphtheria.Biological role

Tellurium has no known biological function, although fungi can incorporate it in place of sulfur and selenium into amino acids such as telluro-cysteine and telluro-methionine.Sony VAIO VGN-TZ16N/B Battery

Organisms have shown a highly variable tolerance to tellurium compounds. Most organisms metabolize tellurium partly to form dimethyl telluride although dimethyl ditelluride is also formed by some species. Dimethyl telluride has been observed in hot springs at very low concentrations.Sony VAIO VGN-TZ17/N Battery

Precautions

Tellurium and tellurium compounds are considered to be mildly toxic and need to be handled with care, although acute poisoning is rare.^[61] Tellurium is not reported to be carcinogenic.^[61]

Humans exposed to as little as 0.01 mg/m³ or less in air develop "tellurium breath", which has a garlic-like odor.Sony VAIO VGN-TZ170N/B Battery

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 is converted into dimethyl telluride, (CH₃)₂Te, which is volatile and is the cause of the garlic-like smell.Sony VAIO VGN-TZ170N/N Battery

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.

Iodine is a chemical element with the symbol I and atomic number 53.Sony VAIO VGN-TZ17GN/B Battery

The name is pronounced  in both American^[2] and British^[3] English.^[4] The name is from the Greek:????? iodes, meaning violet or purple, due to the color of elemental iodine vapor.

Iodine and its compounds are primarily used in nutrition, and industrially in the production of acetic acid and certain polymers.Sony VAIO VGN-TZ17N Battery

Iodine's relatively high atomic number, low toxicity, and ease of attachment to organic compounds have made it a part of many X-ray contrast materials in modern medicine. Iodine has only one stable isotope. A number of iodine radioisotopes are also used in medical applications.Sony VAIO VGN-TZ18/N Battery

Iodine is found on Earth mainly as the highly water-soluble iodide I^-, which concentrates it in oceans and brine pools. Like the other halogens, free iodine occurs mainly as a diatomic molecule I₂, and then only momentarily after being oxidized from iodide by an oxidant like free oxygen.Sony VAIO VGN-TZ180N/RC Battery

In the universe and on Earth, iodine's high atomic number makes it a relatively rare element, ranking 47th in abundance. However, its presence in ocean water has given it a role in biology. It is the heaviest essential element utilized widely by life in biological functions (only tungsten, employed in enzymes by a few species of bacteria, is heavier).Sony VAIO VGN-TZ185N/WC Battery

Iodine's rarity in many soils, due to initial low abundance as a crust-element, and also leaching of soluble iodide by rainwater, has led to many deficiency problems in land animals and inland human populations. Iodine deficiency affects about two billion people and is the leading preventable cause ofintellectual disabilities.Sony VAIO VGN-TZ18GN/X Battery

Iodine is required by higher animals, which use it to synthesize thyroid hormones, which contain the element. Because of this function, radioisotopes of iodine are concentrated in the thyroid gland along with nonradioactive iodine. The radioisotope iodine-131, which has a high fission product yield, concentrates in the thyroid, and is one of the mostcarcinogenic of nuclear fission products.Sony VAIO VGN-TZ18N Battery

Characteristics

Iodine under standard conditions is a bluish-black solid. It can be seen apparently sublimating at standard temperatures into a violet-pink gas that has an irritating odor. This halogen forms compounds with many elements, but is less reactive than the other members of its Group VII (halogens) and has some metallic light reflectance.Sony VAIO VGN-TZ190N/B Battery

Elemental iodine dissolves easily in most organic solvents such as hexane or chloroform owing to its lack of polarity, but is only slightly soluble in water. However, the solubility of elemental iodine in water can be increased by the addition of potassium iodide.Sony VAIO VGN-TZ190N/BC Battery

The molecular iodine reacts reversibly with the negative ion, generating the triiodide anion I₃^? inequilibrium, which is soluble in water. This is also the formulation of some types of medicinal (antiseptic) iodine, although tincture of iodine classically dissolves the element in aqueousethanol.Sony VAIO VGN-TZ191N/XC Battery

The colour of solutions of elemental iodine changes depending on the polarity of the solvent. In non-polar solvents like hexane, solutions are violet; in moderately polar dichloromethane, the solution is dark crimson, and, in strongly polar solvents such as acetone or ethanol, it appears orange or brown. This effect is due to the formation of adducts.Sony VAIO VGN-TZ195N/XC Battery

Iodine melts at the relatively low temperature of 113.7 °C, although the liquid is often obscured by a dense violet vapor of gaseous iodine.

Occurrence

Iodine is rare in the solar system and Earth's crust (47th in abundance); however, iodide salts are often very soluble in water.Sony VAIO VGN-TZ198N/RC Battery

Iodine occurs in slightly greater concentrations in seawaterthan in rocks, 0.05 vs 0.04 ppm. Minerals containing iodine include caliche, found in Chile. The brown algae Laminaria and Fucus found in temperate zones of the Northern Hemisphere contain 0.028–0.454 dry weight percent of iodine.Sony VAIO VGN-TZ250N/B Battery

Aside from tungsten, iodine is the heaviest element to be essential in living organisms, and iodine is the heaviest element thought to be needed by higher animals. About 19,000 tonnes are produced annually from natural sources.

Organoiodine compounds are produced by marine life forms, the most notable being iodomethane(commonly called methyl iodide).Sony VAIO VGN-TZ250N/N Battery

The total iodomethane that is produced by the marine environment, by microbial activity in rice paddies and by the burning of biological material is estimated to be 214 kilotonnes/year.^[7] The volatile iodomethane is broken up in the atmosphere as part of a global iodine cycle.Sony VAIO VGN-TZ250N/P Battery

Structure and bonding

Iodine normally exists as a diatomic molecule with a I-I bond length of 270 pm,  one of the longest single bonds known. The I₂molecules tend to interact via the weak van der Waals force called the London Forces, and this interaction is responsible for the higher melting point compared to more compact halogens, which are also diatomic. Since the atomic size of Iodine is larger, its melting point is higher.Sony VAIO VGN-TZ27/N Battery

The solid crystallizes as orthorhombic crystals. The crystal motif in the Hermann–Mauguin notation is Cmca (No 64), Pearson symbol oS8. The I-I bond is relatively weak, with a bond dissociation energy of 36 kcal/mol. In fact, most bonds to iodine tend to be weaker than for the lighter halides. One consequence of this weak bonding is the relatively high tendency of I₂ molecules to dissociate into atomic iodine.Sony VAIO VGN-TZ270N/B Battery

Production

Of the several places in which iodine occurs in nature, only two sources are useful commercially: the caliche, found in Chile, and the iodine-containing brines of gas and oil fields, especially in Japan and the United States. The caliche, found in Chile, contains sodium nitrate, which is the main product of the mining activities and small amounts of sodium iodate and sodium iodide.Sony VAIO VGN-TZ27N Battery

In the extraction of sodium nitrate, the sodium iodate and sodium iodide are extracted.^[10] The high concentration of iodine in the caliche and the extensive mining made Chile the largest producer of iodine in 2007.

Most other producers use natural occurring brine for the production of iodine.Sony VAIO VGN-TZ28/N Battery

The Japanese Minami Kanto gas field east of Tokyoand the American Anadarko Basin gas field in northwest Oklahoma are the two largest sources for iodine from brine. The brine has a temperature of over 60°C owing to the depth of the source. The brine is first purified and acidified using sulfuric acid, then the iodide present is oxidized to iodine with chlorine.Sony VAIO VGN-TZ285N/RC Battery

An iodine solution is produced, but is dilute and must be concentrated.Air is blown into the solution, causing the iodine to evaporate, then it is passed into an absorbing tower containing acid wheresulfur dioxide is added to reduce the iodine. The hydrogen iodide (HI) is reacted with chlorine to precipitate the iodine. After filtering and purification the iodine is packed.Sony VAIO VGN-TZ28N Battery

2 HI + Cl₂ ? I₂? + 2 HCl

I₂ + 2 H₂O + SO₂ ? 2 HI + H₂SO₄

2 HI + Cl₂ ? I₂? + 2 HCl

The production of iodine from seawater via electrolysis is not used owing to the sufficient abundance of iodine-rich brine. Another source of iodine was kelp, used in the 18th and 19th centuries, but it is no longer economically viable.Sony VAIO VGN-TZ290EAB Battery

Commercial samples often contain high concentrations of impurities, which can be removed by sublimation. The element may also be prepared in an ultra-pure form through the reaction of potassium iodide with copper(II) sulfate, which gives copper(II) iodide initially. That decomposes spontaneously to copper(I) iodide and iodine:

Cu²⁺ + 2 I^– ? CuI₂

2 CuI₂ ? 2 CuI + I₂

There are also other methods of isolating this element in the laboratory, for example, the method used to isolate other halogens: Oxidation of the iodide in hydrogen iodide (often made in situ with an iodide and sulfuric acid) by manganese dioxide (see below in Descriptive chemistry).Sony VAIO VGN-TZ290EAN Battery

Isotopes and their applications

Of the 37 known (characterized) isotopes of iodine, only one, ¹²⁷I, is stable.

The longest-lived radioisotope, ¹²⁹I, has a half-life of 15.7 million years. This is long enough to make it a permanent fixture of the environment on human time scales, but far too short for it to exist as a primordial isotope today.Sony VAIO VGN-TZ290EAP Battery

Instead, iodine-129 is an extinct radionuclide, and its presence in the early solar system is inferred from the observation of an excess of its daughter xenon-129. This nuclide is also newly-made by cosmic rays and as a byproduct of human nuclear fission, which it is used to monitor as a very long-lived environmental contaminant.Sony VAIO VGN-TZ295N/XC Battery

The next-longest-lived radioisotope, iodine-125, has a half-life of 59 days. It is used as a convenient gamma-emitting tag for proteins in biological assays, and a few nuclear medicine imaging tests where a longer half-life is required. It is also commonly used in brachytherapy implanted capsules, which kill tumors by local short-range gamma radiation (but where the isotope is never released into the body).Sony VAIO VGN-TZ298N/XC Battery

Iodine-123 (half-life 13 hours) is the isotope of choice for nuclear medicine imaging of the thyroid gland, which naturally accumulates all iodine isotopes.

Iodine-131 (half-life 8 days) is a beta-emitting isotope, which is a common nuclear fission product.Sony VAIO VGN-TZ33/B Battery

It is preferably administered to humans only in very high doses which destroy all tissues that accumulate it (usually the thyroid), which in turn prevents these tissues from developing cancer from a lower dose (paradoxically, a high dose of this isotope appears safer for the thryoid than a low dose).Sony VAIO VGN-TZ33/N Battery

Like other radioiodines, I-131 accumulates in the thyroid gland, but unlike the others, in small amounts it is highly carcinogenic there, it seems, owing to the high local cell mutation due to damage from beta decay. Because of this tendency of ¹³¹I to cause high damage to cells that accumulate it and other cells near them (0.6 to 2 mm away, the range of the beta rays),Sony VAIO VGN-TZ33/W Battery

it is the only iodine radioisotope used as direct therapy, to kill tissues such as cancers that take up artificially iodinated molecules (example, the compound iobenguane, also known as MIBG). For the same reason, only the iodine isotope I-131 is used to treat Grave's disease and those types of thyroid cancers (sometimes in metastatic form) where the tissue that requires destruction, still functions to naturally accumulate iodide.Sony VAIO VGN-TZ350N/B Battery

Nonradioactive ordinary potassium iodide (iodine-127), in a number of convenient forms (tablets or solution) may be used to saturate the thyroid gland's ability to take up further iodine, and thus protect against accidental contamination from iodine-131 generated by nuclear fission accidents,Sony VAIO VGN-TZ350N/N Battery

such as the Chernobyl disaster and more recently the Fukushima I nuclear accidents, as well as from contamination from this isotope in nuclear fallout from nuclear weapons.

Iodine was discovered by Bernard Courtois in 1811. He was born to a manufacturer of saltpeter (a vital part of gunpowder).Sony VAIO VGN-TZ350N/P Battery

At the time of the Napoleonic Wars,France was at war and saltpeter was in great demand. Saltpeter produced from French niter beds required sodium carbonate, which could be isolated from seaweedcollected on the coasts of Normandy and Brittany. To isolate the sodium carbonate, seaweed was burned and the ash washed with water.Sony VAIO VGN-TZ370N/B Battery

The remaining waste was destroyed by adding sulfuric acid. Courtois once added excessive sulfuric acid and a cloud of purple vapor rose. He noted that the vapor crystallized on cold surfaces, making dark crystals. Courtois suspected that this was a new element but lacked funding to pursue it further.Sony VAIO VGN-TZ37N/G Battery

Courtois gave samples to his friends, Charles Bernard Desormes (1777–1862) and Nicolas Clément (1779–1841), to continue research. He also gave some of the substance to chemist Joseph Louis Gay-Lussac (1778–1850), and to physicist André-Marie Ampère (1775–1836). On 29 November 1813, Dersormes and Clément made public Courtois's discovery.Sony VAIO VGN-TZ37N/P Battery

They described the substance to a meeting of the Imperial Institute of France. On December 6, Gay-Lussac announced that the new substance was either an element or a compound of oxygen. It was Gay-Lussac who suggested the name "iode", from the Greek word ????? (iodes) for violet (because of the color of iodine vapor).Sony VAIO VGN-TZ37N/R Battery

Ampère had given some of his sample to Humphry Davy (1778–1829). Davy did some experiments on the substance and noted its similarity to chlorine.^[18] Davy sent a letter dated December 10 to the Royal Society of London stating that he had identified a new element.Sony VAIO VGN-TZ37N/X Battery

Arguments erupted between Davy and Gay-Lussac over who identified iodine first, but both scientists acknowledged Courtois as the first to isolate the element.

Catalysis

The major application of iodine is as a co-catalyst for the production of acetic acid by the Monsanto and Cativa processes.Sony VAIO VGN-TZ38N/X Battery

In these technologies, which support the world's demand for acetic acid, hydroiodic acid converts the methanol feedstock into methyl iodide, which undergoes carbonylation. Hydrolysis of the resulting acetyl iodide regenerates hydroiodic acid and gives acetic acid.Sony VAIO VGN-TZ398U/XC Battery

Animal feed

The production of ethylenediammonium diiodide (EDDI) consumes a large fraction of available iodine. EDDI is provided to livestock as a nutritional supplement.^[6]

Disinfectant and water treatment

Elemental iodine is used as a disinfectant in various forms.Sony VAIO VGN-TZ50B Battery

The iodine exists as the element, or as the water-soluble triiodide anion I₃^- generated in situ by adding iodide to poorly water-soluble elemental iodine (the reverse chemical reaction makes some free elemental iodine available for antisepsis). In alternative fashion, iodine may come from iodophors, which contain iodine complexed with a solubilizing agent (iodide ion may be thought of loosely as the iodophor in triiodide water solutions).Sony VAIO VGN-TZ90HS Battery

Examples of such preparations include:

• Tincture of iodine: iodine in ethanol, or iodine and sodium iodide in a mixture of ethanol and water.


• Lugol's iodine: iodine and iodide in water alone, forming mostly triiodide. Unlike tincture of iodine, Lugol's has a minimized amount of the free iodine (I₂) component.


• Povidone iodine (an iodophor)Sony VAIO VGN-TZ90NS Battery

Health, medical, and radiological use

In most countries, table salt is iodized. Iodine is required for the essential thyroxin hormones produced by and concentrated in the thyroid gland.

Potassium iodide has been used as an expectorant, although this use is increasingly uncommon. Sony VAIO VGN-TZ90S Battery

In medicine, potassium iodide is used to treat acute thyrotoxicosis, usually as a saturated solution of potassium iodide (SSKI). It is also used to block uptake of iodine-131 in the thyroid gland (see isotopes section above), when this isotope is used as part of radiopharmaceuticals (such as iobenguane) that are not targetted to the thyroid or thyroid type tissues.Sony VAIO VPC CW2MFX/PU Battery

Iodine-131 (in the chemical form of iodide) is a component of nuclear fallout and a particularly dangerous one owing to the thyroid gland's propensity to concentrate ingested iodine, where it is kept for periods longer than this isotope's radiological half-life of eight days.Sony VAIO VPC S11V9E/B Battery

For this reason, if people are expected to be exposed to a significant amount of environmental radioactive iodine (iodine-131 in fallout), they may be instructed to take non-radioactive potassium iodide tablets. The typical adult dose is one 130 mg tablet per 24 hours, supplying 100 mg (100,000 micrograms) iodine, as iodide ion.Sony VAIO VPCB119GJ/B Battery

(Note: typical daily dose of iodine to maintain normal health is of order 100 micrograms; see "Dietary Intake" below.) By ingesting this large amount of non-radioactive iodine, radioactive iodine uptake by the thyroid gland is minimized. See the main article above for more on this topic.Sony VAIO VPCB11AGJ Battery

Radiocontrast agent

Iodine, as a heavy element, is quite radio-opaque. Organic compounds of a certain type (typically iodine-substituted benzene derivatives) are, thus, used in medicine as X-ray radiocontrast agents for intravenous injection. This is often in conjunction with advanced X-ray techniques such as angiography and CT scanning. At present, all water-soluble radiocontrast agents rely on iodine.Sony VAIO VPCB11AVJ Battery

Other uses

Inorganic iodides find specialized uses. Hafnium, zirconium, titanium are purified by the van Arkel Process, which involves the reversible formation of the tetraiodides of these elements. Silver iodide is a major ingredient to traditional photographic film. Thousands of kilograms of silver iodide are consumed annually for cloud seeding.Sony VAIO VPCB11V9E Battery

The organoiodine compound erythrosine is an important food coloring agent. Perfluoroalkyl iodides are precursors to important surfactants, such as perfluorooctanesulfonic acid.

Iodine chemistry

Iodine adopts a variety of oxidation states, commonly ranging from (formally) I⁷⁺ to I^-, and including the intermediate states of I⁵⁺, I³⁺ and I⁺.Sony VAIO VPCB11X9E Battery

Practically, only the 1- oxidation state is of significance, being the form found in iodide salts and organoiodine compounds.

Solubility

Being a nonpolar molecule, iodine is highly soluble in nonpolar organic solvents, including ethanol (20.5 g/100 ml at 15 °C, 21.43 g/100 ml at 25 °C), diethyl ether (20.6 g/100 ml at 17 °C, 25.20 g/100 ml at 25 °C), chloroform, acetic acid, glycerol,Sony VAIO VPCCW18FJ/P Battery

benzene (14.09 g/100 ml at 25 °C), carbon tetrachloride(2.603 g/100 ml at 35 °C), and carbon disulfide (16.47 g/100 ml at 25 °C). Elemental iodine is poorly soluble in water, with one gram dissolving in 3450 ml at 20 °C and 1280 ml at 50 °C. Aqueous and ethanol solutions are brown reflecting the role of these solvents as Lewis bases. Solutions in chloroform, carbon tetrachloride, and carbon disulfide are violet, the color of iodine vapor.Sony VAIO VPCCW18FJ/R Battery

One of the most distinctive properties of iodine is the way that its solubility in water is enhanced by the presence of iodide ions. The dissolution of iodine in aqueous solutions containing iodide (e.g., from hydroiodic acid, potassium iodide, etc.) results from the formation of the I₃^? ion. Dissolved bromides also improve water solubility of iodine.Sony VAIO VPCCW18FJ/W Battery

Redox reactions

In everyday life, iodides are slowly oxidized by atmospheric oxygen in the atmosphere to give free iodine. Evidence for this conversion is the yellow tint of certain aged samples of iodide salts and some organoiodine compounds.Sony VAIO VPCCW19FJ/W Battery

The oxidation of iodide to iodine in air is also responsible for the slow loss of iodide content iniodized salt if exposed to air.^[23] Some salts use iodate to prevent the loss of iodine.

Iodine is easily oxidized and easily reduced. Most common is the interconversion of I^- and I₂. Molecular iodine can be prepared by oxidizing iodides with chlorine:Sony VAIO VPCCW1AFJ Battery

2 I^? + Cl₂ ? I₂ + 2 Cl^?

or with manganese dioxide in acid solution:

2 I^? + 4 H⁺ + MnO₂ ? I₂ + 2 H₂O + Mn²⁺

Iodine is reduced to hydroiodic acid by hydrogen sulfide and hydrazine:Sony VAIO VPCCW1AHJ Battery

8 I₂ + 8 H₂S ? 16 HI + S₈

2 I₂ + N₂H₄ ? 4 HI + N₂

When dissolved in fuming sulfuric acid (65% oleum), iodine forms an intense blue solution. The blue color is due to I+
2 cation, the result of iodine being oxidized bySO₃:

2 I₂ + 2 SO₃ + H₂SO₄ ? 2 I+2 + SO₂ + 2 HSO?
4

The I+
2 cation is also formed in the oxidation of iodine by SbF₅ or TaF₅.Sony VAIO VPCCW1S1E Battery

The resulting I+2Sb₂F?11 or I+2Ta₂F?11 can be isolated as deep blue crystals. The solutions of these salts turn red when cooled below ?60°C, owing to the formation of the I2+4 cation:

2 I+2   I2+4

Under slightly more alkaline conditions, I2+4 disproportionates into I+3 and an iodine(III) compound. Excess iodine can then react with I+3 to form I+5 (green) and I3+15(black).Sony VAIO VPCCW1S1E/B Battery

Oxides of iodine

The best-known oxides are the anions, IO₃^– and IO₄^–, but several other oxides are known, such as the strong oxidant iodine pentoxide.

By contrast with chlorine, the formation of the hypohalite ion (IO^–) in neutral aqueous solutions of iodine is negligible.Sony VAIO VPCCW1S1E/L Battery

I₂ + H₂O   H⁺ + I^? + HIO   (K = 2.0×10^?13)^[24] In basic solutions (such as aqueous sodium hydroxide), iodine converts in a two stage reaction to iodide andiodate:

I2 + 2 OH? ? I? + IO? + H2O		(K = 30)
3 IO? ? 2 I? + IO3?		(K = 1020)

Organic derivatives of hypoiodate (2-Iodoxybenzoic acid, and Dess-Martin periodinane) are used in organic chemistry.Sony VAIO VPCCW1S1E/P Battery

Iodic acid (HIO₃), periodic acid (HIO₄) and their salts are strong oxidizers and are of some use in organic synthesis. Iodine is oxidized to iodate by nitric acid as well as by chlorates:

I₂ + 10 HNO₃ ? 2 HIO₃ + 10 NO₂ + 4 H₂O

I₂ + 2 ClO₃^? ? 2 IO₃^? + Cl₂ Sony VAIO VPCCW1S1E/R Battery

Inorganic iodine compounds

Iodine forms compounds with all the elements except for the noble gases. From the perspective of commercial applications, an important compound is hydroiodic acid, used as a co-catalyst in the Cativa process for the production of acetic acid. Titanium and aluminium iodides are used in the production of butadiene, a precursor to rubber tires.Sony VAIO VPCCW1S1E/W Battery

Alkali metal salts are common colourless solids that are highly soluble in water. Potassium iodide is a convenient source of the iodide anion; it is easier to handle than sodium iodide because it is not hygroscopic. Both salts are mainly used in the production of iodized salt.Sony VAIO VPCCW21FX/B Battery

Sodium iodide is especially useful in the Finkelstein reaction, because it is soluble in acetone, whereas potassium iodide is less so. In this reaction, an alkyl chloride is converted to an alkyl iodide. This relies on the insolubility of sodium chloride in acetone to drive the reaction:Sony VAIO VPCCW21FX/L Battery

R-Cl (acetone) + NaI (acetone) ? R-I (acetone) + NaCl (s)

Despite having the lowest electronegativity of the common halogens, iodine reacts violently with some metals, such as aluminium:

3 I₂ + 2 Al ? 2 AlI₃

This reaction produces 314 kJ per mole of aluminum, comparable to thermite's 425 kJ. Yet the reaction initiates spontaneously, and if unconfined, causes a cloud of gaseous iodine due to the high temperature.Sony VAIO VPCCW21FX/R Battery

Interhalogen compounds

Interhalogen compounds are well known; examples include iodine monochloride and trichloride; iodine pentafluoride and heptafluoride.

Organic compounds

Many organoiodine compounds exist; the simplest is iodomethane, approved as a soil fumigant. Iodinated organic compounds are used as synthetic reagents.Sony VAIO VPCCW21FX/W Battery

Organic synthesis

Organoiodine compounds can be made in many ways. For example, methyl iodide can be prepared from methanol, red phosphorus, and iodine.^[28] The iodinating reagent isphosphorus triiodide that is formed in situ:Sony VAIO VPCCW26EC Battery

3 CH₃OH + PI₃ ? 3 CH₃I + [[H₃PO₃|Phosphorous acid]]

The iodoform test uses an alkaline solution of iodine to react with methyl ketones to give the labile triiodomethide leaving group, forming iodoform, which precipitates.Sony VAIO VPCCW26FX/B Battery

Aryl and alkyl iodides both form Grignard reagents. Iodine is sometimes used to activate magnesium when preparing Grignard reagents. Alkyl iodides such as iodomethane are good alkylating agents. Some drawbacks to use of organoiodine compounds in chemical synthesis are:

Sony AIO VPCCW28EC Battery

• iodine compounds tend to be more expensive than the corresponding bromides and chlorides, in that order


• iodides tend to be much stronger alkylating agents, and so are more toxic (e.g., methyl iodide is very toxic (T+).Sony VAIO VPCCW28FJ/P Battery

• low-molecular-weight iodides tend to have a much higher equivalent weight, compared to other alkylating agents (e.g., methyl iodide versus dimethyl carbonate), owing to the atomic mass of iodine.

Analytical chemistry and bioanalysis

Iodine is a common general stain used in thin-layer chromatography. In particular, iodine forms an intense blue complex with the glucose polymers starch and glycogen. Several analytical methods rely on this property:Sony VAIO VPCCW28FJ/R Battery

• Iodometry. The concentration of an oxidant can be determined by adding it to an excess of iodide, to destroy elemental iodine/triiodide as a result of oxidation by the oxidant. A starch indicator is then used as the indicator close to the end-point, in order to increase the visual contrast (dark blue becomes colorless, instead of the yellow of dilute triiodide becoming colorless).Sony VAIO VPCCW28FJ/W Battery

• An Iodine test may be used to test a sample substance for the presence of starch. The Iodine clock reaction is an extension of the techniques in iodometry.


• Iodine solutions are used in counterfeit banknote detection pens; the premise being that counterfeit banknotes made using commercially available paper contain starch.Sony VAIO VPCCW29FJ/W Battery

• Starch-iodide paper are used to test for the presence of oxidants such as peroxides. The oxidants convert iodide to iodine, which shows up as blue. A solution of starch and iodide can perform the same function.


• During colposcopy, Lugol's iodine is applied to the vagina and cervix.Sony VAIO VPCCW2AFJ Battery

• Normal vaginal tissue stains brown owing to its high glycogen content (a color-reaction similar to that with starch), while abnormal tissue suspicious for cancer does not stain, and thus appears pale compared to the surrounding tissue. Biopsy of suspicious tissue can then be performed. This is called a Schiller's Test.Sony VAIO VPCCW2AHJ Battery

Clandestine synthetic chemical use

In the United States, the Drug Enforcement Agency (DEA) regards iodine and compounds containing iodine (ionic iodides, iodoform, ethyl iodide, and so on) as reagents useful for the clandestine manufacture of methamphetamine.Sony VAIO VPCCW2S1E Battery

Biological role

Iodine is an essential trace element for life, the heaviest element commonly needed by living organisms. Only tungsten, a component of a few bacterial enzymes, has a higher atomic number and atomic weight.

Thyroxines are iodine-containing hormones that justify the widespread use of iodised salt.Sony VAIO VPCCW2S1E/B Battery

Iodine's main role in animal biology is as a constituent of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These are made from addition condensation products of the amino acid tyrosine, and are stored prior to release in an iodine-containingprotein called thyroglobulin. T4 and T3 contain four and three atoms of iodine per molecule, respectively.Sony VAIO VPCCW2S1E/L Battery

The thyroid glandactively absorbs iodide from the blood to make and release these hormones into the blood, actions that are regulated by a second hormone TSH from the pituitary. Thyroid hormones are phylogenetically very old molecules that are synthesized by mostmulticellular organisms, and that even have some effect on unicellular organisms.Sony VAIO VPCCW2S1E/P Battery

Thyroid hormones play a basic role in biology, acting on gene transcription to regulate the basal metabolic rate.^{[citation needed]}The total deficiency of thyroid hormones can reduce basal metabolic rate up to 50%, while in excessive production of thyroid hormones the basal metabolic rate can be increased by 100%.Sony VAIO VPCCW2S1E/R Battery

T4 acts largely as a precursor to T3, which is (with minor exceptions) the biologically active hormone.

Iodine has a nutritional relationship with selenium. A family of selenium-dependent enzymes called deiodinases converts T4 to T3 (the active hormone) by removing an iodine atom from the outer tyrosine ring.Sony VAIO VPCCW2S1E/W Battery

These enzymes also convert T4 to reverse T3 (rT3) by removing an inner ring iodine atom, and convert T3 to 3,3'-diiodothyronine (T2) also by removing an inner ring atom. Both of the latter are inactivated hormones that are ready for disposal and have, in essence, no biological effects.Sony VAIO VPCCW2S5C CN1 Battery

A family of non-selenium-dependent enzymes then further deiodinates the products of these reactions.

Iodine accounts for 65% of the molecular weight of T4 and 59% of the T3. Fifteen to 20 mg of iodine is concentrated in thyroid tissue and hormones, but 70% of the body's iodine is distributed in other tissues, including mammary glands, eyes, gastric mucosa, the cervix, and salivary glands.Sony VAIO VPCF112FX/B Battery

In the cells of these tissues, iodide enters directly by sodium-iodide symporter (NIS). Its role in mammary tissue is related to fetal and neonatal development, but its role in the other tissues is unknown.

Dietary intake

The daily Dietary Reference Intake recommended by the United States Institute of Medicine is between 110 and 130 µg for infants up to 12 months,Sony VAIO VPCF115FG/B Battery

90 µg for children up to eight years, 130 µg for children up to 13 years, 150 µg for adults, 220 µg for pregnant women and 290 µg for lactating mothers.^[34] The Tolerable Upper Intake Level (UL) for adults is 1,100 ?g/day (1.1 mg/day).^[35] The tolerable upper limit was assessed by analyzing the effect of supplementation on thyroid-stimulating hormone.Sony VAIO VPCF116FGBI Battery

The thyroid gland needs no more than 70 micrograms /day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of body systems, including lactating breast, gastric mucosa, salivary glands, oral mucosa, thymus, epidermis, choroid plexus, etc.Sony VAIO VPCF117FJ/W Battery

The high iodide-concentration of thymus tissue in particular suggests an anatomical rationale for this role of iodine in the immune system.^[39] The trophic, antioxidant and apoptosis-inductor actions and the presumed anti-tumour activity of iodides has been suggested to also be important for prevention of oral and salivary glands diseases.Sony VAIO VPCF117HG/BI Battery

Natural sources of iodine include sea life, such as kelp and certain seafood, as well as plants grown on iodine-rich soil. Iodized salt is fortified with iodine.

As of 2000, the median intake of iodine from food in the United States was 240 to 300 ?g/day for men and 190 to 210 ?g/day for women.Sony VAIO VPCF118FJ/W Battery

In Japan, consumption is much higher, owing to the frequent consumption of seaweed or kombu kelp.

After iodine fortification programs (e.g., iodized salt) have been implemented, some cases of iodine-induced hyperthyroidism have been observed (so called Jod-Basedow phenomenon). The condition seems to occur mainly in people over forty, and the risk appears higher when iodine deficiency is severe and the initial rise in iodine intake is high.Sony VAIO VPCF119FC Battery

It should also be noted that information processing, fine motor skills, and visual problem solving are improved by iodine repletion in moderately iodine-deficient children.

Deficiency

In areas where there is little iodine in the diet, typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency gives rise to hypothyroidism, symptoms of which are extreme fatigue, goitre, mental slowing, depression, weight gain, and low basal body temperatures.Sony VAIO VPCF119FC/BI Battery

Iodine deficiency is the leading cause of preventable mental retardation, a result that occurs primarily when babies or small children are rendered hypothyroidic by a lack of the element. The addition of iodine to table salt has largely eliminated this problem in the wealthier nations, but, as of March 2006, iodine deficiency remained a serious public health problem in the developing world.Sony VAIO VPCF119FJ/BI Battery

Iodine deficiency is also a problem in certain areas of Europe.

Other possible health effects being investigated as being related to deficiency include:

• Breast cancer. The breast strongly and actively concentrates iodine into breast-milk for the benefit of the developing infant, and may develop a goiter-like hyperplasia, sometimes manifesting as fibrocystic breast disease, when iodine level are low.Sony VAIO VPCF11AFJ Battery

• Studies indicate that iodine deficiency, either dietary or pharmacologic, can lead to breast atypia and increased incidence of malignancy in animal models, while iodine treatment can reverse dysplasia . The role of iodide in breast dysplasia and development of breast cancer is an area of active research.Sony VAIO VPCF11AGJ Battery

• Stomach cancer. Some researchers have found an epidemiologic correlation between iodine deficiency, iodine-deficient goitre and gastric cancer. A decrease of the incidence of death rate from stomach cancer after implementation of the effective iodine-prophylaxis has been reported also.Sony VAIO VPCF11AHJ Battery

Precautions and toxicity of elemental iodine

Elemental iodine is an oxidizing irritant and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine and Lugol's solution are capable of causing tissue damage if use for cleaning and antisepsis is prolonged.Sony VAIO VPCF11JFX/B Battery

Elemental iodine (I₂) is poisonous if taken orally in larger amounts; 2–3 grams of it is a lethal dose for an adult human.

Iodine vapor is very irritating to the eye, to mucous membranes, and in the respiratory tract. Concentration of iodine in the air should not exceed 1 mg/m³ (eight-hour time-weighted average).Sony VAIO VPCF11M1E Battery

Toxicity of iodide ion

Excess iodine has symptoms similar to those of iodine deficiency. Commonly encountered symptoms are abnormal growth of the thyroid gland and disorders in functioning and growth of the organism as a whole. Iodides are similar in toxicity to bromides.Sony VAIO VPCF11M1E/H Battery

Excess iodine can be more cytotoxic in the presence of selenium deficiency. Iodine supplementation in selenium-deficient populations is, in theory, problematic, partly for this reason.

Iodine sensitivity

Some people develop a sensitivity to iodine. Application of tincture of iodine can cause a rash. Some cases of reaction to Povidone-iodine (Betadine) have been documented to be a chemical burn.Sony VAIO VPCF11MFX/B Battery

Eating iodine-containing foods can cause hives. Medical use of iodine (i.e. as a contrast agent, see above) can causeanaphylactic shock in highly iodine-sensitive patients. Some cases of sensitivity to iodine can be formally classified as iodine allergies. Iodine sensitivity is rare but has a considerable effect given the extremely widespread use of iodine-based contrast media.Sony VAIO VPCF11S1E Battery

Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced  A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized.Sony VAIO VPCF11S1E/B Battery

Naturally occurring xenon consists of nine stable isotopes. There are also over 40 unstable isotopes that undergo radioactive decay. The isotope ratios of xenon are an important tool for studying the early history of the Solar System. Radioactive xenon-135 is produced from iodine-135 as a result ofnuclear fission, and it acts as the most significant neutron absorber in nuclear reactors.Sony VAIO VPCF11Z1E Battery

Xenon is used in flash lamps and arc lamps, and as a general anesthetic. The first excimer laser design used a xenon dimer molecule (Xe₂) as its lasing medium, and the earliest laser designs used xenon flash lamps as pumps. Xenon is also being used to search for hypothetical weakly interacting massive particles and as the propellant for ion thrusters in spacecraft.Sony VAIO VPCF11Z1E/BI Battery

Xenon was discovered in England by William Ramsay and Morris Travers on July 12, 1898, shortly after their discovery of the elements krypton and neon. They found it in the residue left over from evaporating components of liquid air. Ramsay suggested the name xenon for this gas from theGreek word ????? [xenon], neuter singular form of ????? [xenos], meaning 'foreign(er)', 'strange(r)', or 'guest'.Sony VAIO VPCF11ZHJ Battery

In 1902, Ramsay estimated the proportion of xenon in the Earth's atmosphere as one part in 20 million.

During the 1930s, engineer Harold Edgerton began exploring strobe light technology for high speed photography. This led him to the invention of the xenon flash lamp, in which light is generated by sending a brief electrical current through a tube filled with xenon gas. In 1934, Edgerton was able to generate flashes as brief as one microsecond with this method.Sony VAIO VPCF127HGBI Battery

In 1939, Albert R. Behnke Jr. began exploring the causes of "drunkenness" in deep-sea divers. He tested the effects of varying the breathing mixtures on his subjects, and discovered that this caused the divers to perceive a change in depth. From his results, he deduced that xenon gas could serve as ananesthetic.Sony VAIO VPCF137HG/BI Battery

Although Lazharev, in Russia, apparently studied xenon anesthesia in 1941, the first published report confirming xenon anesthesia was in 1946 by J. H. Lawrence, who experimented on mice. Xenon was first used as a surgical anesthetic in 1951 by Stuart C. Cullen, who successfully operated on two patients.Sony VAIO VPCS111FM/S Battery

Xenon and the other noble gases were for a long time considered to be completely chemically inert and not able to form compounds. However, while teaching at the University of British Columbia, Neil Bartlett discovered that the gas platinum hexafluoride (PtF₆) was a powerful oxidizing agent that could oxidize oxygen gas (O₂) to form dioxygenyl hexafluoroplatinate (O₂⁺[PtF₆]^–).Sony VAIO VPCS115EC Battery

Since O₂ and xenon have almost the same first ionization potential, Bartlett realized that platinum hexafluoride might also be able to oxidize xenon. On March 23, 1962, he mixed the two gases and produced the first known compound of a noble gas, xenon hexafluoroplatinate.Sony VAIO VPCS115FG Battery

Bartlett thought its composition to be Xe⁺[PtF₆]^–, although later work has revealed that it was probably a mixture of various xenon-containing salts. Since then, many other xenon compounds have been discovered,  along with some compounds of the noble gases argon, krypton, and radon, including argon fluorohydride (HArF), krypton difluoride (KrF₂), and radon fluoride. By 1971, more than 80 xenon compounds were known.Sony VAIO VPCS117GG Battery

Characteristics

Xenon has atomic number 54; that is, its nucleus contains 54 protons. Atstandard temperature and pressure, pure xenon gas has a density of 5.761 kg/m³, about 4.5 times the surface density of the Earth's atmosphere, 1.217 kg/m³. As a liquid, xenon has a density of up to 3.100 g/mL, with the density maximum occurring at the triple point.Sony VAIO VPCS117GGB Battery

Under the same conditions, the density of solid xenon, 3.640 g/cm³, is higher than the average density of granite, 2.75 g/cm³. Using gigapascals of pressure, xenon has been forced into a metallic phase.

Solid xenon changes from face-centered cubic (fcc) to hexagonal close packed(hcp) crystal phase under pressure and begins to turn metallic at about 140 GPa, with no noticeable volume change in the hcp phase.Sony VAIO VPCS118EC Battery

It is completely metallic at 155 GPa. When metalized, xenon looks sky blue because it absorbs red light and transmits other visible frequencies. Such behavior is unusual for a metal and is explained by the relatively small widths of the electron bands in metallic xenon.

Xenon is a member of the zero-valence elements that are called noble or inert gases.Sony VAIO VPCS119FJ/B Battery

It is inert to most common chemical reactions (such as combustion, for example) because the outer valence shellcontains eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. However, xenon can be oxidized by powerful oxidizing agents, and many xenon compounds have been synthesized.Sony VAIO VPCS119GC Battery

In a gas-filled tube, xenon emits a blue or lavenderish glow when the gas is excited by electrical discharge. Xenon emits a band of emission lines that span the visual spectrum,^[45] but the most intense lines occur in the region of blue light, which produces the coloration.Sony VAIO VPCS11AFJ Battery

Occurrence and production

Xenon is a trace gas in Earth's atmosphere, occurring at 87±1 parts per billion (nL/L), or approximately 1 part per 11.5 million,^[47] and is also found in gases emitted from some mineral springs.

Xenon is obtained commercially as a byproduct of the separation of air into oxygen and nitrogen.Sony VAIO VPCS11AGJ Battery

After this separation, generally performed by fractional distillation in a double-column plant, the liquid oxygen produced will contain small quantities of krypton and xenon. By additional fractional distillation steps, the liquid oxygen may be enriched to contain 0.1–0.2% of a krypton/xenon mixture, which is extracted either via adsorption onto silica gel or by distillation.Sony VAIO VPCS11AHJ Battery

Finally, the krypton/xenon mixture may be separated into krypton and xenon via distillation.  Extraction of a liter of xenon from the atmosphere requires 220 watt-hours of energy.^[50] Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m³.Sony VAIO VPCS11AVJ Battery

Because of its low abundance, xenon is much more expensive than the lighter noble gases—approximate prices for the purchase of small quantities in Europe in 1999 were 10 €/L for xenon, 1 €/L for krypton, and 0.20 €/L for neon.

Within the Solar System, the nucleon fraction of xenon is 1.56 × 10^?8, for an abundance of one part in 64 million of the total mass.Sony VAIO VPCS11J7E/B Battery

Xenon is relatively rare in the Sun's atmosphere, on Earth, and in asteroids and comets. The planet Jupiter has an unusually high abundance of xenon in its atmosphere; about 2.6 times as much as the Sun. This high abundance remains unexplained and may have been caused by an early and rapid buildup of planetesimals—small, subplanetary bodies—before the presolar disk began to heat up.Sony VAIO VPCS11M1E/W Battery

(Otherwise, xenon would not have been trapped in the planetesimal ices.) The problem of the low terrestrial xenon may potentially be explained by covalent bonding of xenon to oxygen within quartz, hence reducing the outgassing of xenon into the atmosphere.Sony VAIO VPCS11V9E Battery

Unlike the lower mass noble gases, the normal stellar nucleosynthesis process inside a star does not form xenon. Elements more massive than iron-56 have a net energy cost to produce through fusion, so there is no energy gain for a star when creating xenon.Sony VAIO VPCS11V9E/B Battery

Instead, xenon is formed during supernova explosions, by the slow neutron capture process (s-process) of red giant stars that have exhausted the hydrogen at their cores and entered the asymptotic giant branch,  in classicalnovae explosions and from the radioactive decay of elements such as iodine, uranium and plutonium.Sony VAIO VPCS11X9E/B Battery

Isotopes and isotopic studies

Naturally occurring xenon is made of nine stable isotopes, the most of any element with the exception of tin, which has ten. Xenon and tin are the only elements to have more than seven stable isotopes.The isotopes ¹²⁴Xe, ¹³⁴Xe and ¹³⁶Xe are predicted to undergo double beta decay, but this has never been observed so they are considered to be stable.Sony VAIO VPCS123FGB Battery

Besides these stable forms, there are over 40 unstable isotopes that have been studied. ¹²⁹Xe is produced by beta decay of ¹²⁹I, which has a half-life of 16 million years, while ^131mXe, ¹³³Xe, ^133mXe, and ¹³⁵Xe are some of the fission products of both ²³⁵U and ²³⁹Pu, and therefore used as indicators of nuclear explosions.Sony VAIO VPCS125EC Battery

Nuclei of two of the stable isotopes of xenon, ¹²⁹Xe and ¹³¹Xe, have non-zero intrinsic angular momenta (nuclear spins, suitable for nuclear magnetic resonance). The nuclear spins can be aligned beyond ordinary polarization levels by means of circularly polarized light and rubidium vapor.Sony VAIO VPCS128EC Battery

The resulting spin polarization of xenon nuclei can surpass 50% of its maximum possible value, greatly exceeding the equilibrium value dictated by the Boltzmann distribution (typically 0.001% of the maximum value at room temperature, even in the strongest magnets). Such non-equilibrium alignment of spins is a temporary condition, and is called hyperpolarization.Sony VAIO VPCS129GC Battery

The process of hyperpolarizing the xenon is called optical pumping (although the process is different from pumping a laser).

Because a ¹²⁹Xe nucleus has a spin of 1/2, and therefore a zero electric quadrupole moment, the ¹²⁹Xe nucleus does not experience any quadrupolar interactions during collisions with other atoms,Sony VAIO VPCS12C7E/B Battery

and thus its hyperpolarization can be maintained for long periods of time even after the laser beam has been turned off and the alkali vapor removed by condensation on a room-temperature surface. Spin polarization of ¹²⁹Xe can persist from several seconds for xenon atoms dissolved in blood to several hours in the gas phase and several days in deeply frozen solid xenon.Sony VAIO VPCS12L9E/B Battery

In contrast, ¹³¹Xe has a nuclear spin value of 3/2 and a nonzero quadrupole moment, and has T₁ relaxation times in the millisecond and second ranges.

Some radioactive isotopes of xenon, for example, ¹³³Xe and ¹³⁵Xe, are produced by neutron irradiation of fissionable material within nuclear reactors.Sony VAIO VPCS12V9E/B Battery

¹³⁵Xe is of considerable significance in the operation of nuclear fission reactors. ¹³⁵Xe has a huge cross section for thermal neutrons, 2.6×10⁶ barns,  so it acts as aneutron absorber or "poison" that can slow or stop the chain reaction after a period of operation. This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production.Sony VAIO VPCY115FGS Battery

Fortunately the designers had made provisions in the design to increase the reactor's reactivity (the number of neutrons per fission that go on to fission other atoms of nuclear fuel).^{[69] 135}Xe reactor poisoning played a major role in the Chernobyl disaster.^[70] A shutdown or decrease of power of a reactor can result in buildup of ₁₃₅Xe and getting the reactor into the iodine pit.Sony VAIO VPCY115FX/BI Battery

Under adverse conditions, relatively high concentrations of radioactive xenon isotopes may be found emanating from nuclear reactors due to the release of fission products from cracked fuel rods, or fissioning of uranium in cooling water.

Because xenon is a tracer for two parent isotopes, xenon isotope ratios in meteorites are a powerful tool for studying the formation of the solar system.Sony VAIO VPCY115FXBI Battery

The iodine-xenon method of dating gives the time elapsed between nucleosynthesis and the condensation of a solid object from the solar nebula. In 1960, physicist John H. Reynolds discovered that certain meteorites contained an isotopic anomaly in the form of an overabundance of xenon-129. He inferred that this was a decay product of radioactive iodine-129.Sony VAIO VPCY118EC Battery

This isotope is produced slowly by cosmic ray spallation and nuclear fission, but is produced in quantity only in supernova explosions. As the half-life of ¹²⁹I is comparatively short on a cosmological time scale, only 16 million years, this demonstrated that only a short time had passed between the supernova and the time the meteorites had solidified and trapped the ¹²⁹I.Sony VAIO VPCY118GX/BI Battery

These two events (supernova and solidification of gas cloud) were inferred to have happened during the early history of the Solar System, as the ¹²⁹I isotope was likely generated before the Solar System was formed, but not long before, and seeded the solar gas cloud with isotopes from a second source. This supernova source may also have caused collapse of the solar gas cloud.Sony VAIO VPCY119FJ/S Battery

In a similar way, xenon isotopic ratios such as ¹²⁹Xe/¹³⁰Xe and ¹³⁶Xe/¹³⁰Xe are also a powerful tool for understanding planetary differentiation and early outgassing. For example, The atmosphere of Mars shows a xenon abundance similar to that of Earth: 0.08 parts per million, however Mars shows a higher proportion of ¹²⁹Xe than the Earth or the Sun.Sony VAIO VPCY11AFJ Battery

As this isotope is generated by radioactive decay, the result may indicate that Mars lost most of its primordial atmosphere, possibly within the first 100 million years after the planet was formed. In another example, excess ¹²⁹Xe found in carbon dioxide well gases fromNew Mexico was believed to be from the decay of mantle-derived gases soon after Earth's formation.Sony VAIO VPCY11AGJ Battery

Compounds

After Neil Bartlett's discovery in 1962 that xenon can form chemical compounds, a large number of xenon compounds have been discovered and described. Almost all known xenon compounds contain the electronegative atoms fluorine or oxygen.Sony VAIO VPCY11AHJ Battery

Halides

Three fluorides are known: XeF₂, XeF₄, and XeF₆. The fluorides are the starting point for the synthesis of almost all xenon compounds.

The solid, crystalline difluoride XeF₂ is formed when a mixture of fluorine and xenon gases is exposed to ultraviolet light.Sony VAIO VPCY11AVJ Battery

Ordinary daylight is sufficient.Long-term heating of XeF₂ at high temperatures under an NiF₂ catalyst yields XeF₆.^[82]Pyrolysis of XeF₆ in the presence of NaF yields high-purity XeF₄.

The xenon fluorides behave as both fluoride acceptors and fluoride donors, forming salts that contain such cations as XeF⁺ and Xe₂F₃⁺, and anions such as XeF₅^?, XeF₇^?, and XeF₈^2?.Sony VAIO VPCY11M1E/S Battery

The green, paramagnetic Xe₂⁺ is formed by the reduction of XeF₂ by xenon gas.

XeF₂ is also able to form coordination complexes with transition metal ions. Over 30 such complexes have been synthesized and characterized.

Whereas the xenon fluorides are well-characterized, the other halides are not known, the only exception being the dichloride,XeCl₂.Sony VAIO VPCY11S1E Battery

Xenon dichloride is reported to be an endothermic, colorless, crystalline compound that decomposes into the elements at 80°C, formed by the high-frequency irradiation of a mixture of xenon, fluorine, and silicon or carbon tetrachloride. However, doubt has been raised as to whether XeCl₂ is a real compound and not merely a van der Waals molecule consisting of weakly bound Xe atoms and Cl₂ molecules.Sony VAIO VPCY11V9E/S Battery

Theoretical calculations indicate that the linear molecule XeCl₂ is less stable than the van der Waals complex.

Oxides and oxohalides

Three oxides of xenon are known: xenon trioxide (XeO₃) and xenon tetroxide (XeO₄), both of which are dangerously explosive and powerful oxidizing agents. Xenon dioxide (XeO₂) was reported in 2011 with a coordination number of four.Sony VAIO VPCY218EC/BI Battery

XeO₂ forms when xenon fluoride is poured over ice. Its crystal structure may allow it to replace silicon in silicate minerals. XeOO⁺ cation has been identified by infrared spectroscopy in solid argon.

Xenon does not react with oxygen directly; the trioxide is formed by the hydrolysis of XeF₆:Sony VAIO VPCY218EC/G Battery

XeF₆ + 3 H₂O ? XeO₃ + 6 HF

XeO₃ is weakly acidic, dissolving in alkali to form unstable xenate salts containing the HXeO?
4 anion. These unstable salts easilydisproportionate into xenon gas and perxenate salts, containing the XeO4?
6 anion.^[91]

Barium perxenate, when treated with concentrated sulfuric acid, yields gaseous xenon tetroxide:Sony VAIO VPCY218EC/L Battery

Ba₂XeO₆ + 2 H₂SO₄ ? 2 BaSO₄ + 2 H₂O + XeO₄

To prevent decomposition, the xenon tetroxide thus formed is quickly cooled to form a pale-yellow solid. It explodes above ?35.9 °C into xenon and oxygen gas.

A number of xenon oxyfluorides are known, including XeOF₂, XeOF₄, XeO₂F₂, and XeO₃F₂. XeOF₂ is formed by the reaction of OF₂ with xenon gas at low temperatures.Sony VAIO VPCY218EC/P Battery

It may also be obtained by the partial hydrolysis of XeF₄. It disproportionates at ?20 °C into XeF₂ and XeO₂F₂. XeOF₄ is formed by the partial hydrolysis ofXeF₆,^[93] or the reaction of XeF₆ with sodium perxenate, Na₄XeO₆. The latter reaction also produces a small amount of XeO₃F₂.Sony VAIO VPCY21S1E/L Battery

XeOF₄ reacts with CsF to form the XeOF?5anion, while XeOF₃ reacts with the alkali metal fluorides KF, RbF and CsF to form the XeOF?4 anion.

Other compounds

Recently, there has been an interest in xenon compounds where xenon is directly bonded to a less electronegative element than fluorine or oxygen, particularlycarbon.Sony VAIO VPCY21S1E/P Battery

Electron-withdrawing groups, such as groups with fluorine substitution, are necessary to stabilize these compounds.^[91] Numerous such compounds have been characterized, including:

• C₆F₅–Xe⁺–N?C–CH₃, where C₆F₅ is the pentafluorophenyl group.


• [C₆F₅]₂Xe


• C₆F₅–Xe–X, where X is CN, F, or Cl.


• R–C?C–Xe⁺, where R is C₂F?
  5 or tert-butyl.


• C₆F₅–XeF+
  2


• (C₆F₅Xe)₂Cl⁺

Other compounds containing xenon bonded to a less electronegative element include F–Xe–N(SO₂F)₂ and F–Xe–BF₂. The latter is synthesized from dioxygenyltetrafluoroborate, O₂BF₄, at ?100 °C.Sony VAIO VPCY21S1E/SI Battery

An unusual ion containing xenon is the tetraxenonogold(II) cation, AuXe2+

4, which contains Xe–Au bonds.^[99] This ion occurs in the compound AuXe₄(Sb₂F₁₁)₂, and is remarkable in having direct chemical bonds between two notoriously unreactive atoms, xenon and gold, with xenon acting as a transition metal ligand.Sony VAIO VPCCW2S5C CN1 Battery

In 1995, M. Räsänen and co-workers, scientists at the University of Helsinki in Finland, announced the preparation of xenon dihydride (HXeH), and later xenon hydride-hydroxide (HXeOH), hydroxenoacetylene (HXeCCH), and other Xe-containing molecules.Sony VAIO VPCEA20 Battery

In 2008, Khriachtchev et al. reported the preparation of HXeOXeH by the photolysis of water within a cryogenic xenon matrix. Deuterated molecules, HXeOD and DXeOH, have also been produced.

Clathrates and excimers

In addition to compounds where xenon forms a chemical bond, xenon can form clathrates—substances where xenon atoms are trapped by the crystalline lattice of another compound.Sony VAIO VPCEB10 Battery

An example is xenon hydrate (Xe·5.75 H₂O), where xenon atoms occupy vacancies in a lattice of water molecules. This clathrate has a melting point of 24 °C.The deuterated version of this hydrate has also been produced. Such clathrate hydrates can occur naturally under conditions of high pressure, such as in Lake Vostok underneath the Antarctic ice sheet.Sony VAIO VPCEB11FM Battery

Clathrate formation can be used to fractionally distill xenon, argon and krypton.

Xenon can also form endohedral fullerene compounds, where a xenon atom is trapped inside a fullerene molecule. The xenon atom trapped in the fullerene can be monitored via ¹²⁹Xe nuclear magnetic resonance (NMR) spectroscopy.Sony VAIO VPCEB11FM/BI Battery

Using this technique, chemical reactions on the fullerene molecule can be analyzed, due to the sensitivity of the chemical shift of the xenon atom to its environment. However, the xenon atom also has an electronic influence on the reactivity of the fullerene.

While xenon atoms are at their ground energy state, they repel each other and will not form a bond.Sony VAIO VPCEB11FM/T Battery

When xenon atoms becomes energized, however, they can form anexcimer (excited dimer) until the electrons return to the ground state. This entity is formed because the xenon atom tends to fill its outermost electronic shell, and can briefly do this by adding an electron from a neighboring xenon atom.Sony VAIO VPCEB11FM/WI Battery

The typical lifetime of a xenon excimer is 1–5 ns, and the decay releases photons withwavelengths of about 150 and 173 nm. Xenon can also form excimers with other elements, such as the halogens bromine, chlorine and fluorine.

Applications

Although xenon is rare and relatively expensive to extract from the Earth's atmosphere, it has a number of applications.Sony VAIO VPCEB11FX Battery

Gas-discharge lamps

Xenon is used in light-emitting devices called xenon flash lamps, which are used in photographic flashes and stroboscopic lamps; to excite the active medium inlasers which then generate coherent light; and, occasionally, in bactericidal lamps. The first solid-state laser, invented in 1960, was pumped by a xenon flash lamp, and lasers used to power inertial confinement fusion are also pumped by xenon flash lamps.Sony VAIO VPCEB11FX/BI Battery

Continuous, short-arc, high pressure xenon arc lamps have a color temperature closely approximating noon sunlight and are used insolar simulators. That is, the chromaticity of these lamps closely approximates a heated black body radiator that has a temperature close to that observed from the Sun.Sony VAIO VPCEB11FX/T Battery

After they were first introduced during the 1940s, these lamps began replacing the shorter-lived carbon arc lamps in movie projectors.^[13] They are employed in typical 35mm and IMAX film projection systems, automotive HID headlights, high-end "tactical" flashlights and other specialized uses.Sony VAIO VPCEB11FX/WI Battery

These arc lamps are an excellent source of short wavelength ultraviolet radiation and they have intense emissions in the near infrared, which is used in some night visionsystems.

The individual cells in a plasma display use a mixture of xenon and neon that is converted into a plasma using electrodes.Sony VAIO VPCEB11GX Battery

The interaction of this plasma with the electrodes generates ultraviolet photons, which then excite the phosphor coating on the front of the display.

Xenon is used as a "starter gas" in high pressure sodium lamps. It has the lowest thermal conductivity and lowest ionization potential of all the non-radioactive noble gases.Sony VAIO VPCEB11GX/BI Battery

As a noble gas, it does not interfere with the chemical reactions occurring in the operating lamp. The low thermal conductivity minimizes thermal losses in the lamp while in the operating state, and the low ionization potential causes the breakdown voltage of the gas to be relatively low in the cold state, which allows the lamp to be more easily started.Sony VAIO VPCEB11GX/T Battery

Lasers

In 1962, a group of researchers at Bell Laboratories discovered laser action in xenon, and later found that the laser gain was improved by adding helium to the lasing medium. The first excimer laser used a xenon dimer (Xe₂) energized by a beam of electrons to produce stimulated emission at an ultraviolet wavelength of 176 nm.Sony VAIO VPCEB11GX/WI Battery

Xenon chloride and xenon fluoride have also been used in excimer (or, more accurately, exciplex) lasers. The xenon chloride excimer laser has been employed, for example, in certain dermatological uses.

Anesthesia

Xenon has been used as a general anesthetic. Although it is expensive, anesthesia machines that can deliver xenon are about to appear on the European market, because advances in recovery and recycling of xenon have made it economically viable.Sony VAIO VPCEB12FX Battery

Two physiological mechanisms for xenon anesthesia have been proposed. The first one involves the inhibition of the calcium ATPase pump—the mechanism cells use to remove calcium (Ca²⁺)—in the cell membrane of synapses. This results from a conformational change when xenon binds to nonpolar sites inside the protein.Sony VAIO VPCEB12FX/BI Battery

The second mechanism focuses on the non-specific interactions between the anesthetic and the lipid membrane.

Xenon has a minimum alveolar concentration (MAC) of 72% at age 40, making it 44% more potent than N₂O as an anesthetic. Thus it can be used in concentrations with oxygen that have a lower risk of hypoxia.Sony VAIO VPCEB12FX/BIC Battery

Unlike nitrous oxide (N₂O), xenon is not a greenhouse gas and so it is also viewed as environmentally friendly. Xenon vented into the atmosphere is being returned to its original source, so no environmental impact is likely.

Neuroprotectant

Xenon is finding application in treating brain injuries, since it is an antagonist of N-methyl-d-aspartate receptors (NMDA receptors).Sony VAIO VPCEB12FX/T Battery

These receptors exacerbate the damage from oxygen deprivation and xenon performs better as a neuroprotectant than either ketamine or nitrous oxide, which have undesired side-effects. Xenon gas was added as an ingredient of the ventilation mix for a newborn baby at St. Michael's Hospital, Bristol, England, whose life chances were otherwise very compromised, and was successful, leading to the authorisation of clinical trials for similar cases.Sony VAIO VPCEB14FX Battery

The treatment is done simultaneously with cooling the body temperature to 33.5 °C.

Imaging

Gamma emission from the radioisotope ¹³³Xe of xenon can be used to image the heart, lungs, and brain, for example, by means of single photon emission computed tomography. ¹³³Xe has also been used to measure blood flow.Sony VAIO VPCEB14FX/BI Battery

Xenon, particularly hyperpolarized ¹²⁹Xe, is a useful contrast agent for magnetic resonance imaging (MRI). In the gas phase, it can be used to image empty space such as cavities in a porous sample or alveoli in lungs. Hyperpolarization renders ¹²⁹Xe much more detectable via magnetic resonance imaging and has been used for studies of the lungs and other tissues.Sony VAIO VPCEB14FX/T Battery

It can be used, for example, to trace the flow of gases within the lungs. Because xenon is soluble in water and also in hydrophobic solvents, it can be used to image various soft living tissues.

NMR spectroscopy

Because of the atom's large, flexible outer electron shell, the NMR spectrum changes in response to surrounding conditions, and can therefore be used as a probe to measure the chemical circumstances around the xenon atom.Sony VAIO VPCEB14FX/WI Battery

For instance xenon dissolved in water, xenon dissolved in hydrophobic solvent, and xenon associated with certain proteins can be distinguished by NMR.

Hyperpolarized xenon can be used by surface-chemists. Normally, it is difficult to characterize surfaces using NMR,Sony VAIO VPCEB15FM Battery

because signals from the surface of a sample will be overwhelmed by signals from the far-more-numerous atomic nuclei in the bulk. However, nuclear spins on solid surfaces can be selectively polarized, bytransferrering spin polarization to them from hyperpolarized xenon gas. This makes the surface signals strong enough to measure, and distinguishes them from bulk signals.Sony VAIO VPCEB15FM/BI Battery

Other

In nuclear energy applications, xenon is used in bubble chambers, probes, and in other areas where a high molecular weight and inert nature is desirable. A by-product of nuclear weapon testing is the release of radioactive xenon-133 and xenon-135. The detection of these isotopes is used to monitor compliance with nucleartest ban treaties, as well as to confirm nuclear test explosions by states such as North Korea.Sony VAIO VPCEB15FM/T Battery

Liquid xenon is being used in calorimeters for measurements of gamma rays as well as a medium for detecting hypotheticalweakly interacting massive particles, or WIMPs. When a WIMP collides with a xenon nucleus, it should, theoretically, strip an electron and create a primary scintillation.Sony VAIO VPCEB15FM/WI Battery

By using xenon, this burst of energy could then be readily distinguished from similar events caused by particles such as cosmic rays. However, the XENON experiment at the Gran Sasso National Laboratory in Italy and the ZEPLIN-II and ZEPLIN-III experiments at the Boulby Underground Laboratory in the UK have thus far failed to find any confirmed WIMPs.Sony VAIO VPCEB15FX Battery

Even if no WIMPs are detected, the experiments will serve to constrain the properties of dark matter and some physics models. The current detector at the Gran Sasso facility has demonstrated sensitivity comparable to that of the best cryogenic detectors, and the sensitivity was expected to be increased by an order of magnitude in 2009.Sony VAIO VPCEB15FX/BI Battery

Xenon is the preferred propellant for ion propulsion of spacecraft because of its low ionization potential per atomic weight, and its ability to be stored as a liquid at near room temperature (under high pressure) yet be easily converted back into a gas to feed the engine.Sony VAIO VPCEB15FX/T Battery

The inert nature of xenon makes it environmentally friendly and less corrosive to an ion engine than other fuels such as mercury or caesium. Xenon was first used for satellite ion engines during the 1970s. It was later employed as a propellant for Europe's SMART-1 spacecraft and for the three ion propulsion engines on NASA's Dawn Spacecraft.Sony VAIO VPCEB15FX/WI Battery

Chemically, the perxenate compounds are used as oxidizing agents in analytical chemistry. Xenon difluoride is used as an etchant for silicon, particularly in the production of microelectromechanical systems (MEMS). The anticancer drug 5-fluorouracil can be produced by reacting xenon difluoride with uracil.Sony VAIO VPCEB16FX Battery

Xenon is also used in protein crystallography. Applied at pressures from 0.5 to 5 MPa (5 to 50 atm) to a protein crystal, xenon atoms bind in predominantly hydrophobic cavities, often creating a high quality, isomorphous, heavy-atom derivative, which can be used for solving the phase problem.Sony VAIO VPCEB16FX/B Battery

Precautions

Many oxygen-containing xenon compounds are toxic due to their strong oxidative properties, and explosive due to their tendency to break down into elemental xenon plus diatomic oxygen (O₂), which contains much stronger chemical bonds than the xenon compounds.Sony VAIO VPCEB16FX/G Battery

Xenon gas can be safely kept in normal sealed glass or metal containers at standard temperature and pressure. However, it readily dissolves in most plastics and rubber, and will gradually escape from a container sealed with such materials. Xenon is non-toxic, although it does dissolve in blood and belongs to a select group of substances that penetrate the blood-brain barrier, causing mild to full surgical anesthesia when inhaled in high concentrations with oxygen.Sony VAIO VPCEB16FX/L Battery

At 169 m/s, the speed of sound in xenon gas is slower than that in air due to the slower average speed of the heavy xenon atoms compared to nitrogen and oxygen molecules. Hence, xenon lowers the resonant frequencies of the vocal tract when inhaled. This produces a characteristic lowered voice timbre, an effect opposite to the high-timbred voice caused by inhalation of helium.Sony VAIO VPCEB16FX/P Battery

Like helium, xenon does not satisfy the body's need for oxygen. Xenon is both a simple asphyxiant and an anesthetic more powerful than nitrous oxide; consequently, many universities no longer allow the voice stunt as a general chemistry demonstration. As xenon is expensive, the gas sulfur hexafluoride, which is similar to xenon in molecular weight (146 versus 131), is generally used in this stunt, and is an asphyxiant without being anesthetic.Sony VAIO VPCEB16FX/W Battery

It is possible to safely breathe heavy gases such as xenon or sulfur hexafluoride when they are in a mixture with oxygen; the oxygen comprising at least 20% of the mixture. Xenon at 80% concentration along with 20% oxygen rapidly produces the unconsciousness of general anesthesia (and has been used for this, as discussed above).Sony VAIO VPCEB17FX Battery

Breathing mixes gases of different densities very effectively and rapidly so that heavier gases are purged along with the oxygen, and do not accumulate at the bottom of the lungs. There is, however, a danger associated with any heavy gas in large quantities: it may sit invisibly in a container, and if a person enters a container filled with an odorless, colorless gas, they may find themselves breathing it unknowingly. Sony VAIO VPCEB17FX/B Battery

Xenon is rarely used in large enough quantities for this to be a concern, though the potential for danger exists any time a tank or container of xenon is kept in an unventilated space.Sony VAIO VPCEB17FX/G Battery,Sony VAIO VPCEB17FX/L Battery,Sony VAIO VPCEB17FX/P Battery,Sony VAIO VPCEB17FX/W Battery,Sony VAIO VPCEB190X Battery,Sony VAIO VPCEB19FX Battery,Sony VAIO VPCEB19GX Battery