Instruct: Given a question, retrieve passages that answer the question.
Query: What elements are in the chalcogen group?
The chalcogens (/ˈkælkədʒɪnz/) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive element polonium (Po). The chemically uncharacterized synthetic element livermorium (Lv) is predicted to be a chalcogen as well.[1] 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 word khalkόs (χαλκός) principally meaning copper (the term was also used for bronze/brass, any metal in the poetic sense, ore or coin),[2] and the Latinised Greek word genēs, meaning born or produced.[3][4]
Seventeen elements are known to form binary hexafluorides. Nine of these elements are transition metals, three are actinides, four are chalcogens, and one is a noble gas. Most hexafluorides are molecular compounds with low melting and boiling points. Four hexafluorides (S, Se, Te, and W) are gases at room temperature (25 °C) and a pressure of 1 atm, two are liquids (Re, Mo), and the others are volatile solids. The group 6, chalcogen, and noble gas hexafluorides are colourless, but the other hexafluorides have colours ranging from white, through yellow, orange, red, brown, and grey, to black.
A means of comparing the chalcogen-chalcogen bonding forces with H-bonding is to compare the effect of various solvent environments on the chalcogen-chalcogen bond. This has been done on a series of molecules featuring a chalcogen-chalcogen intramolecular bond in one conformation (closed) and exposed to solvent interactions in another (open). One such study found that the preference for the closed conformation showed almost no dependence on the solvent environment. This was taken to mean that changes in solvent dipole moment, polarizability, or H-bonding character did not influence the balance between chalcogen-chalcogen bonding and solvent interactions. Such a conclusion would mean that the dispersion forces and electrostatic forces involved in chalcogen-chalcogen bonding do not majorly influence the interaction. Instead, this would mean that the orbital interaction dominates the bonding interaction.
Chalcogens form single bonds and double bonds with other carbon group elements than carbon, such as silicon, germanium, and tin. Such compounds typically form from a reaction of carbon group halides and chalcogenol salts or chalcogenol bases. 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 group hydrides react or when heavier versions of carbenes react. Sulfur and tellurium can bond with organic compounds containing both silicon and phosphorus.[30]
Zinc makes up about 75 ppm (0.0075%) of Earth's crust, making it the 24th most abundant element. Soil contains zinc in 5–770 ppm with an average 64 ppm. Seawater has only 30 ppb and the atmosphere, 0.1–4 µg/m. The element is normally found in association with other base metals such as copper and lead in ores. Zinc is a chalcophile, meaning the element is more likely to be found in minerals together with sulfur and other heavy chalcogens, rather than with the light chalcogen oxygen or with non-chalcogen electronegative elements such as the halogens. Sulfides formed as the crust solidified under the reducing conditions of the early Earth's atmosphere. Sphalerite, which is a form of zinc sulfide, is the most heavily mined zinc-containing ore because its concentrate contains 60–62% zinc.
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.[57] Because sulfide minerals are much denser than the silicate minerals formed by lithophile elements,[51] 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.[58]
The chalcogens—the elements in group 16 of the periodic table—particularly sulfur (S), selenium (Se) and tellurium (Te)—react with more electropositive elements, such as silver, to form chalcogenides. These are extremely versatile compounds, in that they can be crystalline or amorphous, metallic or semiconducting, and conductors of ions or electrons. Glass containing chalcogenides can be used to make fibers for far infrared transmission.
A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements of the periodic table are defined as chalcogens, the term chalcogenide is more commonly reserved for sulfides, selenides, tellurides, and polonides, rather than oxides. Many metal ores exist as chalcogenides. Photoconductive chalcogenide glasses are used in xerography. Some pigments and catalysts are also based on chalcogenides. The metal dichalcogenide MoS is a common solid lubricant.
Elemental chalcogens react with certain lanthanide compounds to form lanthanide clusters rich in chalcogens. Uranium(IV) chalcogenol compounds also exist. There are also transition metal chalcogenols which have potential to serve as catalysts and stabilize nanoparticles.[30]
Lighter chalcogens are typically nontoxic in their elemental form, and are often critical to life, while the heavier chalcogens are typically toxic.[1] All of the chalcogens have some role in biological functions, either as a nutrient or a toxin. The lighter chalcogens, such as oxygen and sulfur, are rarely toxic and usually helpful in their pure form. Selenium is an important nutrient but is also commonly toxic.[6] Tellurium often has unpleasant effects (although some organisms can use it), and polonium is always extremely harmful, both in its chemical toxicity and its radioactivity.
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 strike-anywhere matches and quantum 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. The decrease in the number of chalcogen-phosphorus compounds further down the periodic table is due to diminishing bond strength. Such compounds tend at least one phosphorus atom in the center, surrounded by four chalcogens and side chains. However, some phosphorus-chalcogen compounds also contain hydrogen (such as secondary phosphine 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 other pnictogens, such as arsenic, antimony, and bismuth. Heavier chalcogen pnictides tend to form ribbon-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. 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 of equilibrium with chalcogenophosphinous acid. Secondary phosphine chalcogenides are weak acids.[30] 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).[35]
Chalcogen bonding in catalysis has been used to pre-orient substrate, allowing for asymmetric/stereoselective catalysis on the preferred conformation of the substrate. Examples include an asymmetric acyl transfer on an enantiomeric mixture catalyzed by a chiral isothiourea. The acyl group is first transfer on to the chiral catalyst which is purported to go through a transition state featuring a 1,5 chalcogen bonding interaction on the catalyst which orients the acyl group prior to transfer on to the substrate. This resulted in one enantiomer of the substrate acylated and the remaining substrate enriched in the other enantiomer. Similar interactions have been invoked in stereoselective Michael additions and β-lactonizations.
Although all group 16 elements of the periodic table, including oxygen, can be defined as chalcogens, oxygen and oxides are usually distinguished from chalcogens and chalcogenides. The term chalcogenide is more commonly reserved for sulfides, selenides, and tellurides, rather than for oxides.[29][30][31]
Due to a chalcogen's ability to function as an electron donor, many systems will balance between hydrogen bonding with the chalcogen as a donor or chalcogen bonding. This balance can be observed in a series of self-bonding intermolecular interactions between various substituted chalcogens. In cases with hard chalcogen atoms as acceptors, the balance favors H-bonding between chalcogen and methyl H. However, as the acceptor atoms move down the group, chalcogen-chalcogen bonding will be favored. It is hypothesized that electrostatic forces should only dominate in a chalcogen-chalcogen bond with lighter congeners, and instead that dispersion forces dominate in the cases of heavier congeners
In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in group 16 as the heaviest chalcogen, although it has not been confirmed to behave as the heavier homologue to the chalcogen polonium. Livermorium is calculated to have some similar properties to its lighter homologues (oxygen, sulfur, selenium, tellurium, and polonium), and be a post-transition metal, although it should also show several major differences from them.
Any electron donor can donate electrons into the σ-hole of a bonded chalcogen, including halogen anions, amines, and π electrons (such as benzene). Similar to halogen bonding, chalcogen bonding can occur between two chalcogens, resulting in a chalcogen-chalcogen bond. Non-covalent interactions are well characterized by Bader's atoms in molecules (AIM) model which defines a bond as any bond-critical point (BCP) existing between two nuclei. This can be understood simply as a saddle point on an electron density map of a molecule. Hydrogen and halogen bonds are both well characterized by this method. The same analysis has been performed on chalcogen bonds, as shown below. The BCP's between S and Cl in these molecules are evidence of the non-covalent interactions, in this case chalcogen-halogen bonds.
Another method used to evaluate chalcogen bonding specifically and a wide range of bonding generally is natural bond orbital (NBO) analysis. NBO analysis distinguishes between covalent, Lewis-type bonding interactions and non-covalent, non-Lewis bonding interaction. The chalcogen bond will be evaluated based on the natural population of the n → σ* orbital. A higher population of this orbital should then also be reflected in changes in the geometry.
Three of the chalcogens (sulfur, selenium, and tellurium) were part of the discovery of periodicity, as they are among a series of triads of elements in the same group that were noted by Johann Wolfgang Döbereiner as having similar properties.[10] Around 1865 John 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 the octaves of music.[39][40] His version included a "group b" consisting of oxygen, sulfur, selenium, tellurium, and osmium.
The chalcogens (oxygen's periodic table column) are somewhat similar: The tetrafluorides are thermally unstable and hydrolyze, and are also ready to use their lone pair to form adducts to other (acidic) fluorides. Sulfur and selenium tetrafluorides are molecular while TeF is a polymer. The hexafluorides are the result of direct fluorination of the elements (compare: other hexahalides of these elements do not even exist). They increase in reactivity with atomic number: SF is extremely inert, SeF is less noble (for example, reacts with ammonia at 200 °C (400 °F)), and TeF easily hydrolyzes to give an oxoacid. Oxygen's highest fluoride is oxygen difluoride, but fluorine can theoretically (as of 2012) oxidize it to a uniquely high oxidation state of +4 in the fluorocation: . In addition, several chalcogen fluorides occur which have more than chalcogen (OF, SF, etc.).
Chalcogen derivatives are known for all of the main group elements except the noble gases. Usually, their stoichiometries follow the classical valence trends, e.g. SiS, BS, SbS. Many exceptions exist however, e.g. PS and SN. The structures of many of main group materials are dictated, not by close packing, but by directional covalent bonding.
The Goldschmidt classification,
developed by Victor Goldschmidt (1888-1947), is a geochemical classification which groups the chemical elements within the Earth according to their preferred host phases into lithophile (rock-loving), siderophile (iron-loving), chalcophile (ore-loving or chalcogen-loving), and atmophile (gas-loving) or volatile (the element, or a compound in which it occurs, is liquid or gaseous at ambient surface conditions).
In chemistry, a group (also known as a family) is a column of elements in the periodic table of the chemical elements. There are 18 numbered groups in the periodic table, and the f-block columns (between groups 3 and 4) are not numbered. The elements in a group have similar physical or chemical characteristics of the outermost electron shells of their atoms (i.e., the same core charge), as most chemical properties are dominated by the orbital location of the outermost electron.
There are three systems of group numbering. The modern numbering "group 1" to "group 18" is recommended by the International Union of Pure and Applied Chemistry (IUPAC). It replaces two older naming schemes that were mutually confusing. Also, groups may be identified by their topmost element or have a specific name. For example, group 16 is variously described as the "oxygen group" and as the chalcogens.
In history, several sets of group names have been used:
Since 1990, a number of borides 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 of dimethyl sulfide attached to a boron-hydrogen molecule. Other important boron-chalcogen compounds include macropolyhedral 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.[37]
The alkali metals can also react analogously with the heavier chalcogens (sulfur, selenium, tellurium, and polonium), and all the alkali metal chalcogenides are known (with the exception of francium's). Reaction with an excess of the chalcogen can similarly result in lower chalcogenides, with chalcogen ions containing chains of the chalcogen atoms in question. For example, sodium can react with sulfur to form the sulfide (NaS) and various polysulfides with the formula NaS ("x" from 2 to 6), containing the ions. Due to the basicity of the Se and Te ions, the alkali metal selenides and tellurides are alkaline in solution; when reacted directly with selenium and tellurium, alkali metal polyselenides and polytellurides are formed along with the selenides and tellurides with the and ions. They may be obtained directly from the elements in liquid ammonia or when air is not present, and are colourless, water-soluble compounds that air oxidises quickly back to selenium or tellurium. The alkali metal polonides are all ionic compounds containing the Po ion; they are very chemically stable and can be produced by direct reaction of the elements at around 300–400 °C.
In the 19th century, Jons Jacob Berzelius suggested calling the elements in group 16 "amphigens",[43] as the elements in the group formed amphid salts (salts of oxyacids[44][45]) The term received some use in the early 1800s but is now obsolete.[43] The name chalcogen comes from the Greek words χαλκος (chalkos, literally "copper"), and γενές (genes, born,[46] gender, kindle). It was first used in 1932 by Wilhelm Biltz's group at the University of Hanover, where it was proposed by Werner Fischer.[29] The word "chalcogen" gained popularity in Germany during the 1930s because the term was analogous to "halogen".[47] Although the literal meanings of the Greek words imply that chalcogen 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,[48] as the vast majority of metal ores are chalcogenides and the word χαλκος in ancient Greek was associated with metals and metal-bearing rock in general; copper, and its alloy bronze, was one of the first metals to be used by humans.
The four lightest chalcogens (oxygen, sulfur, selenium, and tellurium) are all primordial elements on Earth. Sulfur and oxygen occur as constituent copper ores and selenium and tellurium occur in small traces in such ores.[25] Polonium forms naturally after the decay of other elements, even though it is not primordial. Livermorium does not occur naturally at all.