Thechalcogens (ore forming) (/ˈkælkədʒənz/KAL-kə-jənz) are thechemical elements ingroup 16 of theperiodic table.[1] This group is also known as theoxygen family. Group 16 consists of the elementsoxygen (O),sulfur (S),selenium (Se),tellurium (Te), and theradioactive elementspolonium (Po) andlivermorium (Lv).[2] Often, oxygen is treated separately from the other chalcogens, sometimes even excluded from the scope of the term "chalcogen" altogether, due to its very different chemical behavior from sulfur, selenium, tellurium, and polonium. The word "chalcogen" is derived from a combination of the Greek wordkhalkos (χαλκός) principally meaningcopper (the term was also used forbronze,brass, any metal in the poetic sense,ore andcoin),[3] and the Latinized Greek wordgenēs, meaningborn orproduced.[4][5]
Sulfur has been known since antiquity, and oxygen was recognized as an element in the 18th century. Selenium, tellurium and polonium were discovered in the 19th century, and livermorium in 2000. All of the chalcogens have sixvalence electrons, leaving them two electrons short of a full outer shell. Their most commonoxidation states are −2, +2, +4, and +6. They have relatively lowatomic radii, especially the lighter ones.[6]
All of the naturally occurring chalcogens have some role in biological functions, either as a nutrient or a toxin. Selenium is an important nutrient (among others as a building block ofselenocysteine) but is also commonly toxic.[7] Tellurium often has unpleasant effects (althoughsome organisms can use it), and polonium (especially theisotopepolonium-210) is always harmful as a result of its radioactivity.
Sulfur has more than 20allotropes, oxygen has nine, selenium has at least eight, polonium has two, and only one crystal structure of tellurium has so far been discovered. There are numerous organic chalcogen compounds. Not counting oxygen, organic sulfur compounds are generally the most common, followed by organic selenium compounds and organic tellurium compounds. This trend also occurs with chalcogenpnictides and compounds containing chalcogens andcarbon group elements.
Oxygen is generally obtained byseparation of air into nitrogen and oxygen.[8] Sulfur is extracted from oil and natural gas. Selenium and tellurium are produced as byproducts of copper refining. Polonium is most available in naturally occurring actinide-containing materials. Livermorium has been synthesized in particle accelerators. The primary use of elemental oxygen is insteelmaking.[9] Sulfur is mostly converted intosulfuric acid, which is heavily used in the chemical industry.[7] Selenium's most common application is glassmaking. Tellurium compounds are mostly used in optical disks, electronic devices, and solar cells. Some of polonium's applications are due to its radioactivity.[2]
Chalcogens show similar patterns inelectron configuration, especially in the outermostshells, where they all have the same number ofvalence electrons, resulting in similar trends in chemical behavior:
All chalcogens have sixvalence electrons. All of the solid, stable chalcogens are soft[11] and do notconduct heat well.[6]Electronegativity decreases towards the chalcogens with higher atomic numbers. Density, melting and boiling points, andatomic andionic radii[12] tend to increase towards the chalcogens with higher atomic numbers.[6]
Out of the six known chalcogens, one (oxygen) has an atomic number equal to a nuclearmagic number, which means that theiratomic nuclei tend to have increased stability towards radioactive decay.[13] Oxygen has three stable isotopes, and 14 unstable ones. Sulfur has four stable isotopes, 20 radioactive ones, and oneisomer. Selenium has sixobservationally stable or nearly stable isotopes, 26 radioactive isotopes, and 9 isomers. Tellurium has eight stable or nearly stable isotopes, 31 unstable ones, and 17 isomers. Polonium has 42 isotopes, none of which are stable.[14] It has an additional 28 isomers.[2] In addition to the stable isotopes, some radioactive chalcogen isotopes occur in nature, either because they are decay products, such as210Po, because they areprimordial, such as82Se, because ofcosmic rayspallation, or vianuclear fission of uranium. Livermorium isotopes288Lv through293Lv have been discovered; the most stable livermorium isotope is293Lv, which has a half-life of 0.061 seconds.[2][15]
With the exception of livermorium, all chalcogens have at least one naturally occurringradioisotope: oxygen has trace15O, sulfur has trace35S, selenium has82Se, tellurium has128Te and130Te, and polonium has210Po.
Among the lighter chalcogens (oxygen and sulfur), the most neutron-poor isotopes undergoproton emission, the moderately neutron-poor isotopes undergoelectron capture orβ+ decay, the moderately neutron-rich isotopes undergoβ− decay, and the most neutron rich isotopes undergoneutron emission. The middle chalcogens (selenium and tellurium) have similar decay tendencies as the lighter chalcogens, but no proton-emitting isotopes have been observed, and some of the most neutron-deficient isotopes of tellurium undergoalpha decay. Polonium isotopes tend to decay via alpha or beta decay.[16] Isotopes with nonzeronuclear spins are more abundant in nature among the chalcogens selenium and tellurium than they are with sulfur.[17]
Phase diagram of sulfur showing the relative stabilities of several allotropes[18]The four stable chalcogens atSTPPhase diagram forsolid oxygen
Oxygen's most commonallotrope is diatomic oxygen, or O2, a reactive paramagnetic molecule that is ubiquitous toaerobic organisms and has a blue color in itsliquid state. Another allotrope is O3, orozone, which is three oxygen atoms bonded together in a bent formation. There is also an allotrope calledtetraoxygen, or O4,[19] and six allotropes ofsolid oxygen including "red oxygen", which has the formula O8.[20]
Sulfur has over 20 known allotropes, which is more than any other element exceptcarbon.[21] The most common allotropes are in the form of eight-atom rings, but other molecular allotropes that contain as few as two atoms or as many as 20 are known. Other notable sulfur allotropes includerhombic sulfur andmonoclinic sulfur. Rhombic sulfur is the more stable of the two allotropes. Monoclinic sulfur takes the form of long needles and is formed when liquid sulfur is cooled to slightly below its melting point. The atoms in liquid sulfur are generally in the form of long chains, but above 190 °C, the chains begin to break down. If liquid sulfur above 190 °C isfrozen very rapidly, the resulting sulfur is amorphous or "plastic" sulfur. Gaseous sulfur is a mixture of diatomic sulfur (S2) and 8-atom rings.[22]
Selenium has at least eight distinct allotropes.[23] The gray allotrope, commonly referred to as the "metallic" allotrope, despite not being a metal, is stable and has a hexagonalcrystal structure. The gray allotrope of selenium is soft, with aMohs hardness of 2, and brittle. Four other allotropes of selenium aremetastable. These include twomonoclinic red allotropes and twoamorphous allotropes, one of which is red and one of which is black.[24] The red allotrope converts to the black allotrope in the presence of heat. The gray allotrope of selenium is made fromspirals on selenium atoms, while one of the red allotropes is made of stacks of selenium rings (Se8).[2][dubious –discuss]
Tellurium is not known to have any allotropes,[25] although its typical form is hexagonal. Polonium has two allotropes, which are known as α-polonium and β-polonium.[26] α-polonium has a cubic crystal structure and converts to the rhombohedral β-polonium at 36 °C.[2]
Oxygen, sulfur, and selenium arenonmetals, and tellurium is ametalloid, meaning that its chemical properties are between those of ametal and those of a nonmetal.[7] It is not certain whether polonium is a metal or a metalloid. Some sources refer to polonium as a metalloid,[2][27] although it has some metallic properties. Also, some allotropes of selenium display characteristics of a metalloid,[28] even though selenium is usually considered a nonmetal. Even though oxygen is a chalcogen, its chemical properties are different from those of other chalcogens. One reason for this is that the heavier chalcogens have vacantd-orbitals. Oxygen's electronegativity is also much higher than those of the other chalcogens. This makes oxygen'selectric polarizability several times lower than those of the other chalcogens.[17]
Theoxidation number of the most common chalcogen compounds with positive metals is −2. However the tendency for chalcogens to form compounds in the −2 state decreases towards the heavier chalcogens.[29] Other oxidation numbers, such as −1 inpyrite andperoxide, do occur. The highest formaloxidation number is +6.[6] This oxidation number is found insulfates,selenates,tellurates, polonates, and their corresponding acids, such assulfuric acid.
Sulfur's oxidation states are −2, +2, +4, and +6. Sulfur-containing analogs of oxygen compounds often have the prefixthio-. Sulfur's chemistry is similar to oxygen's, in many ways. One difference is that sulfur-sulfurdouble bonds are far weaker than oxygen-oxygen double bonds, but sulfur-sulfursingle bonds are stronger than oxygen-oxygen single bonds.[30] Organic sulfur compounds such asthiols have a strong specific smell, and a few are utilized by some organisms.[2]
Although all group 16 elements of the periodic table, including oxygen, can be defined as chalcogens, oxygen and oxides are usually distinguished from chalcogens andchalcogenides. The termchalcogenide is more commonly reserved forsulfides,selenides, andtellurides, rather than foroxides.[33][34][35]
Except for polonium, the chalcogens are all fairly similar to each other chemically. They all form X2− ions when reacting withelectropositive metals.[29]
Sulfide minerals and analogous compounds produce gases upon reaction with oxygen.[36]
Chalcogens also form compounds withhalogens known aschalcohalides, orchalcogen halides. The majority of simple chalcogen halides are well-known and widely used as chemicalreagents. However, more complicated chalcogen halides, such as sulfenyl, sulfonyl, and sulfuryl halides, are less well known to science. Out of the compounds consisting purely of chalcogens and halogens, there are a total of 13 chalcogen fluorides, nine chalcogen chlorides, eight chalcogen bromides, and six chalcogen iodides that are known.[dubious –discuss] The heavier chalcogen halides often have significant molecular interactions. Sulfur fluorides with low valences are fairly unstable and little is known about their properties.[dubious –discuss] However, sulfur fluorides with high valences, such assulfur hexafluoride, are stable and well-known.Sulfur tetrafluoride is also a well-known sulfur fluoride. Certain selenium fluorides, such asselenium difluoride, have been produced in small amounts. The crystal structures of bothselenium tetrafluoride andtellurium tetrafluoride are known. Chalcogen chlorides and bromides have also been explored. In particular, selenium dichloride and sulfur dichloride can react to formorganic selenium compounds. Dichalcogen dihalides, such as Se2Cl2 also are known to exist. There are also mixed chalcogen-halogen compounds. These include SeSX, with X being chlorine or bromine.[dubious –discuss] Such compounds can form in mixtures ofsulfur dichloride and selenium halides. These compounds have been fairly recently structurally characterized, as of 2008. In general, diselenium and disulfur chlorides and bromides are useful chemical reagents. Chalcogen halides with attached metal atoms are soluble in organic solutions.[dubious –discuss] One example of such a compound isMoS2Cl3. Unlike selenium chlorides and bromides, seleniumiodides have not been isolated, as of 2008, although it is likely that they occur in solution. Diselenium diiodide, however, does occur in equilibrium with selenium atoms and iodine molecules. Some tellurium halides with low valences, such asTe2Cl2 andTe2Br2, formpolymers when in thesolid state. These tellurium halides can be synthesized by the reduction of pure tellurium withsuperhydride and reacting the resulting product with tellurium tetrahalides. Ditellurium dihalides tend to get less stable as the halides become lower in atomic number and atomic mass. Tellurium also forms iodides with even fewer iodine atoms than diiodides. These include TeI and Te2I. These compounds have extended structures in the solid state. Halogens and chalcogens can also form halochalcogenateanions.[34]
Alcohols,phenols and other similar compounds contain oxygen. However, inthiols,selenols andtellurols; sulfur, selenium, and tellurium replace oxygen. Thiols are better known than selenols or tellurols. Aside from alcohols, thiols are the most stable chalcogenols and tellurols are the least stable, being unstable in heat or light. Other organic chalcogen compounds includethioethers,selenoethers and telluroethers. Some of these, such asdimethyl sulfide,diethyl sulfide, anddipropyl sulfide are commercially available. Selenoethers are in the form ofR2Se orRSeR. Telluroethers such asdimethyl telluride are typically prepared in the same way as thioethers and selenoethers. Organic chalcogen compounds, especially organic sulfur compounds, have the tendency to smell unpleasant. Dimethyl telluride also smells unpleasant,[37] andselenophenol is renowned for its "metaphysical stench".[38] There are alsothioketones,selenoketones, andtelluroketones. Out of these, thioketones are the most well-studied with 80% of chalcogenoketones papers being about them. Selenoketones make up 16% of such papers and telluroketones make up 4% of them. Thioketones have well-studied non-linear electric and photophysical properties. Selenoketones are less stable than thioketones and telluroketones are less stable than selenoketones. Telluroketones have the highest level ofpolarity of chalcogenoketones.[34]
There is a very large number of metal chalcogenides. There are also ternary compounds containingalkali metals andtransition metals. Highly metal-rich metal chalcogenides, such asLu7Te and Lu8Te have domains of the metal's crystal lattice containing chalcogen atoms. While these compounds do exist, analogous chemicals that containlanthanum,praseodymium,gadolinium,holmium,terbium, orytterbium have not been discovered, as of 2008. Theboron group metals aluminum,gallium, andindium also form bonds to chalcogens. The Ti3+ ion forms chalcogenidedimers such as TiTl5Se8. Metal chalcogenide dimers also occur as lower tellurides, such as Zr5Te6.[34]
Elemental chalcogens react with certain lanthanide compounds to form lanthanide clusters rich in chalcogens.[dubious –discuss]Uranium(IV) chalcogenol compounds also exist. There are alsotransition metal chalcogenols which have potential to serve ascatalysts and stabilizenanoparticles.[34]
Compounds with chalcogen-phosphorus bonds have been explored for more than 200 years. These compounds include unsophisticated phosphorus chalcogenides as well as large molecules with biological roles and phosphorus-chalcogen compounds with metal clusters. These compounds have numerous applications, including organo-phosphate insecticides,strike-anywhere matches andquantum dots. A total of 130,000 compounds with at least one phosphorus-sulfur bond, 6000 compounds with at least one phosphorus-selenium bond, and 350 compounds with at least one phosphorus-tellurium bond have been discovered.[citation needed] The decrease in the number of chalcogen-phosphorus compounds further down the periodic table is due to diminishing bond strength. Such compounds tend to have at least one phosphorus atom in the center, surrounded by four chalcogens andside chains. However, some phosphorus-chalcogen compounds also contain hydrogen (such as secondaryphosphine chalcogenides) or nitrogen (such as dichalcogenoimidodiphosphates).Phosphorus selenides are typically harder to handle that phosphorus sulfides, and compounds in the form PxTey have not been discovered. Chalcogens also bond with otherpnictogens, such asarsenic,antimony, andbismuth. Heavier chalcogen pnictides tend to formribbon-like polymers instead of individual molecules. Chemical formulas of these compounds include Bi2S3 and Sb2Se3. Ternary chalcogen pnictides are also known. Examples of these include P4O6Se and P3SbS3.salts containing chalcogens and pnictogens also exist. Almost all chalcogen pnictide salts are typically in the form of [PnxE4x]3−, where Pn is a pnictogen and E is a chalcogen.[dubious –discuss] Tertiary phosphines can react with chalcogens to form compounds in the form of R3PE, where E is a chalcogen. When E is sulfur, these compounds are relatively stable, but they are less so when E is selenium or tellurium. Similarly, secondary phosphines can react with chalcogens to form secondary phosphine chalcogenides. However, these compounds are in a state ofequilibrium with chalcogenophosphinous acid. Secondary phosphine chalcogenides areweak acids.[34] Binary compounds consisting of antimony or arsenic and a chalcogen. These compounds tend to be colorful and can be created by a reaction of the constituent elements at temperatures of 500 to 900 °C (932 to 1,652 °F).[39]
Chalcogens form single bonds and double bonds with othercarbon group elements than carbon, such assilicon,germanium, andtin. Such compounds typically form from a reaction of carbon group halides and chalcogenol salts or chalcogenolbases. Cyclic compounds with chalcogens, carbon group elements, and boron atoms exist, and occur from the reaction of boron dichalcogenates and carbon group metal halides. Compounds in the form of M-E, where M is silicon, germanium, or tin, and E is sulfur, selenium or tellurium have been discovered. These form when carbon grouphydrides react or when heavier versions ofcarbenes react.[dubious –discuss] Sulfur and tellurium can bond with organic compounds containing both silicon and phosphorus.[34]
All of the chalcogens formhydrides. In some cases this occurs with chalcogens bonding with two hydrogen atoms.[2] Howevertellurium hydride andpolonium hydride are both volatile and highlylabile.[40] Also, oxygen can bond to hydrogen in a 1:1 ratio as inhydrogen peroxide, but this compound is unstable.[29]
Since 1990, a number ofborides with chalcogens bonded to them have been detected. The chalcogens in these compounds are mostly sulfur, although some do contain selenium instead. One such chalcogen boride consists of two molecules ofdimethyl sulfide attached to a boron-hydrogen molecule. Other important boron-chalcogen compounds includemacropolyhedral systems. Such compounds tend to feature sulfur as the chalcogen. There are also chalcogen borides with two, three, or four chalcogens. Many of these contain sulfur but some, such as Na2B2Se7 contain selenium instead.[41]
Early attempts to separate oxygen from air were hampered by the fact that air was thought of as a single element up to the 17th and 18th centuries.Robert Hooke,Mikhail Lomonosov,Ole Borch, andPierre Bayden all successfully created oxygen, but did not realize it at the time. Oxygen was discovered byJoseph Priestley in 1774 when he focused sunlight on a sample ofmercuric oxide and collected the resulting gas.Carl Wilhelm Scheele had also created oxygen in 1771 by the same method, but Scheele did not publish his results until 1777.[2]
Tellurium was first discovered in 1783 byFranz Joseph Müller von Reichenstein. He discovered tellurium in a sample of what is now known as calaverite. Müller assumed at first that the sample was pure antimony, but tests he ran on the sample did not agree with this. Muller then guessed that the sample wasbismuth sulfide, but tests confirmed that the sample was not that. For some years, Muller pondered the problem. Eventually he realized that the sample was gold bonded with an unknown element. In 1796, Müller sent part of the sample to the German chemistMartin Klaproth, who purified the undiscovered element. Klaproth decided to call the element tellurium after the Latin word for earth.[2]
Selenium was discovered in 1817 byJöns Jacob Berzelius. Berzelius noticed a reddish-brown sediment at a sulfuric acid manufacturing plant. The sample was thought to contain arsenic. Berzelius initially thought that the sediment contained tellurium, but came to realize that it also contained a new element, which he named selenium after the Greek moon goddess Selene.[2][42]
Dmitri Mendeleev's periodic system proposed in 1871 showing oxygen, sulfur, selenium and tellurium part of his group VI
Three of the chalcogens (sulfur, selenium, and tellurium) were part of the discovery ofperiodicity, as they are among a series of triads of elements in the samegroup that were noted byJohann Wolfgang Döbereiner as having similar properties.[13] Around 1865John Newlands produced a series of papers where he listed the elements in order of increasing atomic weight and similar physical and chemical properties that recurred at intervals of eight; he likened such periodicity to theoctaves of music.[43][44] His version included a "group b" consisting of oxygen, sulfur, selenium, tellurium, andosmium.
Johann Wolfgang Döbereiner was among the first to notice similarities between what are now known as chalcogens.
After 1869,Dmitri Mendeleev proposed his periodic table placing oxygen at the top of "group VI" above sulfur, selenium, and tellurium.[45]Chromium,molybdenum,tungsten, anduranium were sometimes included in this group, but they would be later rearranged as part ofgroup VIB; uranium would later be moved to theactinide series. Oxygen, along with sulfur, selenium, tellurium, and later polonium would be grouped ingroup VIA, until the group's name was changed togroup 16 in 1988.[46]
In the late 19th century,Marie Curie andPierre Curie discovered that a sample ofpitchblende was emitting four times as much radioactivity as could be explained by the presence of uranium alone. The Curies gathered several tons of pitchblende and refined it for several months until they had a pure sample of polonium. The discovery officially took place in 1898. Prior to the invention of particle accelerators, the only way to produce polonium was to extract it over several months from uranium ore.[2]
The first attempt at creating livermorium was from 1976 to 1977 at theLBNL, who bombarded curium-248 with calcium-48, but were not successful. After several failed attempts in 1977, 1998, and 1999 by research groups in Russia, Germany, and the US, livermorium was created successfully in 2000 at theJoint Institute for Nuclear Research by bombardingcurium-248 atoms with calcium-48 atoms. The element was known as ununhexium until it was officially named livermorium in 2012.[2]
In the 19th century,Jons Jacob Berzelius suggested calling the elements in group 16 "amphigens",[47] as the elements in the group formedamphid salts (salts ofoxyacids,[48][49] formerly regarded as composed of two oxides, an acid and a basic oxide). The term received some use in the early 1800s but is now obsolete.[47] The namechalcogen comes from the Greek wordsχαλκος (chalkos, literally "copper"), andγενές (genes, born,[50] gender, kindle). It was first used in 1932 byWilhelm Biltz's group atLeibniz University Hannover, where it was proposed byWerner Fischer.[33] The word "chalcogen" gained popularity in Germany during the 1930s because the term was analogous to "halogen".[51] Although the literal meanings of the modern Greek words imply thatchalcogen means "copper-former", this is misleading because the chalcogens have nothing to do with copper in particular. "Ore-former" has been suggested as a better translation,[52] as the vast majority of metal ores are chalcogenides and the wordχαλκος in ancient Greek was associated with metals and metal-bearing rock in general; copper, and its alloybronze, was one of the first metals to be used by humans.
Oxygen's name comes from the Greek wordsoxy genes, meaning "acid-forming". Sulfur's name comes from either the Latin wordsulfurium or theSanskrit wordsulvere; both of those terms are ancient words for sulfur. Selenium is named after the Greek goddess of the moon,Selene, to match the previously discovered element tellurium, whose name comes from the Latin wordtelus, meaning earth. Polonium is named after Marie Curie's country of birth, Poland.[7] Livermorium is named for theLawrence Livermore National Laboratory.[53]
The four lightest chalcogens (oxygen, sulfur, selenium, and tellurium) are allprimordial elements on Earth. Sulfur and oxygen occur as constituentcopper ores and selenium and tellurium occur in small traces in such ores.[29]Polonium forms naturally from the decay of other elements, even though it is not primordial. Livermorium does not occur naturally at all.
Oxygen makes up 21% of the atmosphere by weight, 89% of water by weight, 46% of the Earth's crust by weight,[6] and 65% of the human body.[54] Oxygen also occurs in many minerals, being found in alloxide minerals andhydroxide minerals, and in numerous other mineral groups.[55] Stars of at least eight times the mass of the Sun also produce oxygen in their cores vianuclear fusion.[13] Oxygen is the third-mostabundant element in the universe, making up 1% of the universe by weight.[56][57]
Sulfur makes up 0.035% of the Earth's crust by weight, making it the 17th most abundant element there[6] and makes up 0.25% of the human body.[54] It is a major component of soil. Sulfur makes up 870 parts per million of seawater and about 1 part per billion of the atmosphere.[2] Sulfur can be found in elemental form or in the form ofsulfide minerals,sulfate minerals, orsulfosalt minerals.[55] Stars of at least 12 times the mass of the Sun produce sulfur in their cores via nuclear fusion.[13] Sulfur is the tenth most abundant element in the universe, making up 500 parts per million of the universe by weight.[56][57]
Selenium makes up 0.05parts per million of the Earth's crust by weight.[6] This makes it the 67th mostabundant element in the Earth's crust. Selenium makes up on average 5 parts per million of thesoils.Seawater contains around 200 parts per trillion of selenium. The atmosphere contains 1nanogram of selenium per cubic meter. There are mineral groups known asselenates andselenites, but there are not many minerals in these groups.[58] Selenium is not produced directly by nuclear fusion.[13] Selenium makes up 30 parts per billion of the universe by weight.[57]
There are only 5 parts per billion of tellurium in the Earth's crust and 15 parts per billion of tellurium in seawater.[2] Tellurium is one of the eight or nine least abundant elements in the Earth's crust.[7] There are a few dozentellurate minerals andtelluride minerals, and tellurium occurs in some minerals with gold, such assylvanite and calaverite.[59] Tellurium makes up 9 parts per billion of the universe by weight.[7][57][60]
Polonium only occurs in trace amounts on Earth, via radioactive decay of uranium and thorium. It is present in uranium ores in concentrations of 100 micrograms per metric ton. Very minute amounts of polonium exist in the soil and thus in most food, and thus in the human body.[2] The Earth's crust contains less than 1 part per billion of polonium, making it one of the ten rarest metals on Earth.[2][6]
Livermorium is always produced artificially inparticle accelerators. Even when it is produced, only a small number of atoms are synthesized at a time.
Chalcophile elements are those that remain on or close to the surface because they combine readily with chalcogens other than oxygen, forming compounds which do not sink into the core. Chalcophile ("chalcogen-loving") elements in this context are those metals and heavier nonmetals that have a low affinity for oxygen and prefer to bond with the heavier chalcogen sulfur as sulfides.[61] Because sulfide minerals are much denser than the silicate minerals formed bylithophile elements,[55] chalcophile elements separated below the lithophiles at the time of the first crystallisation of the Earth's crust. This has led to their depletion in the Earth's crust relative to their solar abundances, though this depletion has not reached the levels found with siderophile elements.[62]
Approximately 100 millionmetric tons of oxygen are produced yearly. Oxygen is most commonly produced byfractional distillation, in which air is cooled to a liquid, then warmed, allowing all the components of air except for oxygen to turn to gases and escape. Fractionally distilling air several times can produce 99.5% pure oxygen.[63] Another method with which oxygen is produced is to send a stream of dry, clean air through a bed ofmolecular sieves made ofzeolite, which absorbs the nitrogen in the air, leaving 90 to 93% pure oxygen.[2]
Sulfur recovered from oil refining in Alberta, stockpiled for shipment inNorth Vancouver, British Columbia
Sulfur can be mined in its elemental form, although this method is no longer as popular as it used to be. In 1865 a large deposit of elemental sulfur was discovered in the U.S. states of Louisiana and Texas, but it was difficult to extract at the time. In the 1890s,Herman Frasch came up with the solution of liquefying the sulfur with superheated steam and pumping the sulfur up to the surface. These days sulfur is instead more often extracted fromoil,natural gas, andtar.[2]
The world production of selenium is around 1500 metric tons per year, out of which roughly 10% is recycled. Japan is the largest producer, producing 800 metric tons of selenium per year. Other large producers include Belgium (300 metric tons per year), the United States (over 200 metric tons per year), Sweden (130 metric tons per year), and Russia (100 metric tons per year). Selenium can be extracted from the waste from the process of electrolytically refining copper. Another method of producing selenium is to farm selenium-gathering plants such asmilk vetch. This method could produce three kilograms of selenium per acre, but is not commonly practiced.[2]
Tellurium is mostly produced as a by-product of the processing of copper.[64] Tellurium can also be refined byelectrolytic reduction ofsodium telluride. The world production of tellurium is between 150 and 200 metric tons per year. The United States is one of the largest producers of tellurium, producing around 50 metric tons per year. Peru, Japan, and Canada are also large producers of tellurium.[2]
Until the creation of nuclear reactors, all polonium had to be extracted from uranium ore. In modern times, mostisotopes of polonium are produced by bombardingbismuth with neutrons.[7] Polonium can also be produced by highneutron fluxes innuclear reactors. Approximately 100 grams of polonium are produced yearly.[65] All the polonium produced for commercial purposes is made in the Ozersk nuclear reactor in Russia. From there, it is taken toSamara, Russia for purification, and from there toSt. Petersburg for distribution. The United States is the largest consumer of polonium.[2]
Alllivermorium is produced artificially inparticle accelerators. The first successful production of livermorium was achieved by bombarding curium-248 atoms withcalcium-48 atoms. As of 2011, roughly 25 atoms of livermorium had been synthesized.[2]
Metabolism is the most important source and use of oxygen. Minor industrial uses includeSteelmaking (55% of all purified oxygen produced), thechemical industry (25% of all purified oxygen), medical use,water treatment (as oxygen kills some types of bacteria),rocket fuel (in liquid form), and metal cutting.[2]
Most sulfur produced is transformed intosulfur dioxide, which is further transformed intosulfuric acid, a very common industrial chemical. Other common uses include being a key ingredient ofgunpowder andGreek fire, and being used to changesoil pH.[7] Sulfur is also mixed into rubber tovulcanize it. Sulfur is used in some types ofconcrete andfireworks. 60% of all sulfuric acid produced is used to generatephosphoric acid.[2][66] Sulfur is used as apesticide (specifically as anacaricide andfungicide) on "orchard, ornamental, vegetable, grain, and other crops."[67]
Around 40% of all selenium produced goes toglassmaking. 30% of all selenium produced goes tometallurgy, includingmanganese production. 15% of all selenium produced goes toagriculture. Electronics such asphotovoltaic materials claim 10% of all selenium produced.Pigments account for 5% of all selenium produced. Historically, machines such asphotocopiers andlight meters used one-third of all selenium produced, but this application is in steady decline.[2]
Some of polonium's applications relate to the element's radioactivity. For instance, polonium is used as analpha-particle generator for research. Polonium alloyed withberyllium provides an efficient neutron source. Polonium is also used in nuclear batteries. Most polonium is used in antistatic devices.[2][6] Livermorium does not have any uses whatsoever due to its extreme rarity and short half-life.
Organochalcogen compounds are involved in thesemiconductor process. These compounds also feature intoligand chemistry andbiochemistry. One application of chalcogens themselves is to manipulateredox couples in supramolecular chemistry (chemistry involving non-covalent bond interactions). This application leads on to such applications as crystal packing, assembly of large molecules, and biological recognition of patterns. The secondary bonding interactions of the larger chalcogens, selenium and tellurium, can create organic solvent-holdingacetylenenanotubes. Chalcogen interactions are useful for conformational analysis and stereoelectronic effects, among other things. Chalcogenides with through bonds also have applications. For instance,divalent sulfur can stabilize carbanions,cationic centers, andradical. Chalcogens can confer upon ligands (such as DCTO) properties such as being able to transformCu(II) to Cu(I). Studying chalcogen interactions gives access to radical cations, which are used in mainstreamsynthetic chemistry. Metallic redox centers of biological importance are tunable by interactions of ligands containing chalcogens, such asmethionine andselenocysteine. Also, chalcogen through-bonds[dubious –discuss] can provide insight about the process of electron transfer.[17]
DNA, an important biological compound containing oxygen
Oxygen is needed by almost allorganisms for the purpose of generatingATP. It is also a key component of most other biological compounds, such as water,amino acids andDNA. Human blood contains a large amount of oxygen. Human bones contain 28% oxygen. Human tissue contains 16% oxygen. A typical 70-kilogram human contains 43 kilograms of oxygen, mostly in the form of water.[2]
All animals need significant amounts ofsulfur. Some amino acids, such ascysteine andmethionine contain sulfur. Plant roots take up sulfate ions from the soil and reduce it to sulfide ions.Metalloproteins also use sulfur to attach to useful metal atoms in the body and sulfur similarly attaches itself to poisonous metal atoms likecadmium to haul them to the safety of the liver. On average, humans consume 900 milligrams of sulfur each day. Sulfur compounds, such as those found in skunk spray often have strong odors.[2]
All animals and some plants need trace amounts ofselenium, but only for some specialized enzymes.[7][68] Humans consume on average between 6 and 200 micrograms of selenium per day. Mushrooms andbrazil nuts are especially noted for their high selenium content. Selenium in foods is most commonly found in the form of amino acids such asselenocysteine andselenomethionine.[2] Selenium can protect againstheavy metal poisoning.[68]
Tellurium is not known to be needed for animal life, although a few fungi can incorporate it in compounds in place of selenium. Microorganisms also absorb tellurium and emitdimethyl telluride. Most tellurium in the blood stream is excreted slowly in urine, but some is converted to dimethyl telluride and released through the lungs. On average, humans ingest about 600 micrograms of tellurium daily. Plants can take up some tellurium from the soil. Onions and garlic have been found to contain as much as 300parts per million of tellurium in dry weight.[2]
Polonium has no biological role, and is highly toxic on account of being radioactive.
Oxygen is generally nontoxic, butoxygen toxicity has been reported when it is used in high concentrations. In both elemental gaseous form and as a component of water, it is vital to almost all life on Earth. Despite this, liquid oxygen is highly dangerous.[7] Even gaseous oxygen is dangerous in excess. For instance,sports divers have occasionally drowned fromconvulsions caused by breathing pure oxygen at a depth of more than 10 meters (33 feet) underwater.[2] Oxygen is also toxic to somebacteria.[54] Ozone, an allotrope of oxygen, is toxic to most life. It can causelesions in the respiratory tract.[69]
Sulfur is generally nontoxic and is even a vital nutrient for humans. However, in its elemental form it can cause redness in the eyes and skin, a burning sensation and a cough if inhaled, a burning sensation and diarrhoea and/orcatharsis[67] if ingested, and can irritate the mucous membranes.[70][71] An excess of sulfur can be toxic forcows because microbes in therumens of cows produce toxic hydrogen sulfide upon reaction with sulfur.[72] Many sulfur compounds, such ashydrogen sulfide (H2S) andsulfur dioxide (SO2) are highly toxic.[2]
Selenium is a trace nutrient required by humans on the order of tens or hundreds of micrograms per day. A dose of over 450 micrograms can be toxic, resulting in bad breath andbody odor. Extended, low-level exposure, which can occur at some industries, results inweight loss,anemia, anddermatitis. In many cases of selenium poisoning,selenous acid is formed in the body.[73]Hydrogen selenide (H2Se) is highly toxic.[2]
Exposure to tellurium can produce unpleasant side effects. As little as 10 micrograms of tellurium per cubic meter of air can cause notoriously unpleasant breath, described as smelling like rotten garlic.[7] Acute tellurium poisoning can cause vomiting, gut inflammation, internal bleeding, and respiratory failure. Extended, low-level exposure to tellurium causes tiredness and indigestion.Sodium tellurite (Na2TeO3) is lethal in amounts of around 2 grams.[2]
Amphid salts was a name given byJons Jacob Berzelius in the 19th century for chemical salts derived from the 16th group of the periodic table which includedoxygen,sulfur,selenium, andtellurium.[76] The term received some use in the early 1800s but is now obsolete.[77] The current term in use for the 16th group is chalcogens.
^Emsley, John (2011).Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. pp. 375–383,412–415,475–481,511–520,529–533, 582.ISBN978-0-19-960563-7.
^Van Vleet, JF; Boon, GD; Ferrans, VJ (1981)."Tellurium compounds". The Toxicology and Environmental Health Information Program, US National Institutes of Health. RetrievedNovember 25, 2013.
^Newlands, John A. R. (August 18, 1865)."On the Law of Octaves".Chemical News.12: 83.Archived from the original on January 1, 2011. RetrievedNovember 25, 2013.
^Mendelejew, Dimitri (1869). "Über die Beziehungen der Eigenschaften zu den Atomgewichten der Elemente".Zeitschrift für Chemie (in German):405–406.
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