Editing Chalcogen (section)

==Properties==
===Atomic and physical===
Chalcogens show similar patterns in [[electron configuration]], especially in the outermost [[electron shell|shells]], where they all have the same number of [[valence electron]]s, resulting in similar trends in chemical behavior:

{| class="wikitable" style="white-space:nowrap;"
|-
!''[[Atomic number|Z]]'' !! [[Chemical element|Element]] !! [[Electron shell|Electrons per shell]]
|-
| 8 || Oxygen || 2, 6
|-
| 16 || Sulfur || 2, 8, 6
|-
| 34 || Selenium || 2, 8, 18, 6
|-
| 52 || Tellurium || 2, 8, 18, 18, 6
|-
| 84 || Polonium || 2, 8, 18, 32, 18, 6
|-
| 116 || Livermorium || 2, 8, 18, 32, 32, 18, 6 ''(predicted)''<ref name=Haire>{{Cite book |publisher= [[Springer Science+Business Media]] |location=Dordrecht, The Netherlands |bibcode=2011tcot.book.....M |doi =10.1007/978-94-007-0211-0 |editor1-last=Morss |editor1-first=Lester R. |editor2-last=Edelstein |editor2-first=Norman M. |editor3-last=Fuger| editor3-first=Jean |isbn =978-94-007-0210-3 |last1= Morss |first1= Lester R. |last2= Edelstein |first2= Norman M. |last3= Fuger |first3= Jean |year = 2011 |title = The Chemistry of the Actinide and Transactinide Elements }}</ref>
|}

{|class="wikitable" style="text-align:center"
|-
!Element !! Melting point<br />(°C)<ref name="Jackson2002" />
! Boiling point<br />(°C)<ref name="Jackson2002" />
!Density at STP<br />(g/cm<sup>3</sup>)<ref name="Jackson2002" />
|-
|Oxygen || −219 || −183 
|0.00143
|-
|Sulfur || 120 || 445 
|2.07
|-
|Selenium || 221 || 685 
|4.3
|-
|Tellurium || 450 || 988 
|6.24
|-
|Polonium || 254 || 962 
|9.2
|-
|Livermorium || 364–507 (predicted) || 762–862 (predicted) 
|14 (predicted)<ref name=Haire/>
|}

All chalcogens have six [[valence electron]]s. All of the solid, stable chalcogens are soft<ref>{{cite book|editor-last=Samsonov |editor-first=G. V. |chapter=Mechanical Properties of the Elements|doi=10.1007/978-1-4684-6066-7_7|isbn=978-1-4684-6066-7|chapter-url=http://ihtik.lib.ru/2011.08_ihtik_nauka-tehnika/2011.08_ihtik_nauka-tehnika_3560.rar|title=Handbook of the physicochemical properties of the elements|pages=387–446|publisher=IFI-Plenum|place=New York, USA|year=1968|url-status=dead|archive-url=https://web.archive.org/web/20150402123344/http://ihtik.lib.ru/2011.08_ihtik_nauka-tehnika/2011.08_ihtik_nauka-tehnika_3560.rar|archive-date=April 2, 2015|df=mdy-all}}</ref> and do not [[thermal conductivity|conduct heat]] well.<ref name="Jackson2002" /> [[Electronegativity]] decreases towards the chalcogens with higher atomic numbers. Density, melting and boiling points, and [[atomic radius|atomic]] and [[ionic radius|ionic radii]]<ref name="rsc">{{cite web |url=http://www.rsc.org/chemsoc/visualelements/pages/data/intro_groupvi_data.html |title=Visual Elements: Group 16 |publisher=Royal Society of Chemistry |access-date=November 25, 2013}}</ref> tend to increase towards the chalcogens with higher atomic numbers.<ref name="Jackson2002">{{cite book |last=Jackson |first=Mark |title=Periodic Table Advanced |publisher=Bar Charts Inc. |isbn=978-1-57222-542-8 |year=2002}}</ref>

===Isotopes===
Out of the six known chalcogens, one (oxygen) has an atomic number equal to a nuclear [[Magic number (physics)|magic number]], which means that their [[atomic nuclei]] tend to have increased stability against radioactive decay.<ref name="The Disappearing Spoon"/> Oxygen has three stable isotopes, and 14 unstable ones. Sulfur has four stable isotopes, 20 radioactive ones, and one [[nuclear isomer|isomer]]. Selenium has six [[observationally 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.<ref>{{cite web|last = Sonzogniurl|first = Alejandro|url = http://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=84&n=130|title = Double Beta Decay for Selenium-82|access-date = November 25, 2013|publisher = Brookhaven National Laboratory|archive-date = October 3, 2021|archive-url = https://web.archive.org/web/20211003183335/https://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=84&n=130|url-status = dead}}</ref> It has an additional 28 isomers.<ref name="ReferenceB"/> In addition to the stable isotopes, some radioactive chalcogen isotopes occur in nature, either because they are decay products, such as [[polonium-210|<sup>210</sup>Po]], because they are [[primordial nuclide|primordial]], such as <sup>82</sup>Se, because of [[cosmic ray]] [[spallation]], or via [[nuclear fission]] of uranium. Livermorium isotopes <sup>288</sup>Lv through <sup>293</sup>Lv have been discovered; the most stable livermorium isotope is <sup>293</sup>Lv, which has a half-life of 0.061 seconds.<ref name = "ReferenceB"/><ref>{{cite journal|year = 1973|title = Double Beta Decay of Selenium-82|doi = 10.2113/gsecongeo.68.2.252|journal = Economic Geology|volume = 68|issue = 2|page = 252|last1 = Srinivasan|first1 = B.|last2 = Alexander|first2 = E. C.|last3 = Beaty|first3 = R. D.|last4 = Sinclair|first4 = D. E.|last5 = Manuel|first5 = O. K.| bibcode=1973EcGeo..68..252S }}</ref>

With the exception of livermorium, all chalcogens have at least one naturally occurring [[radioisotope]]: oxygen has trace <sup>15</sup>O, sulfur has trace <sup>35</sup>S, selenium has <sup>82</sup>Se, tellurium has <sup>128</sup>Te and <sup>130</sup>Te, and polonium has <sup>210</sup>Po.

Among the lighter chalcogens (oxygen and sulfur), the most neutron-poor isotopes undergo [[proton emission]], the moderately neutron-poor isotopes undergo [[electron capture]] or [[beta plus decay|β<sup>+</sup> decay]], the moderately neutron-rich isotopes undergo [[beta decay|β<sup>−</sup> decay]], and the most neutron rich isotopes undergo [[neutron 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 undergo [[alpha decay]]. Polonium isotopes tend to decay via alpha or beta decay.<ref>{{cite web |url=http://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=47&n=63 |title=Nudat 2 |publisher=Nndc.bnl.gov |access-date=November 25, 2013 |archive-date=July 14, 2017 |archive-url=https://web.archive.org/web/20170714190234/http://www.nndc.bnl.gov/nudat2/reCenter.jsp?z=47&n=63 |url-status=dead }}</ref> Isotopes with nonzero [[nuclear spin]]s are more abundant in nature among the chalcogens selenium and tellurium than they are with sulfur.<ref name="synth"/>

===Allotropes===
{{see also|Allotropes of oxygen|Allotropes of sulfur}}
[[File:Phase diagram of sulfur (1975).png|thumb|upright=1.2|Phase diagram of sulfur showing the relative stabilities of several allotropes<ref>{{cite web|url=https://www.osti.gov/biblio/4010212 |title=Phase Diagrams of the Elements|author=Young, David A. |date=September 11, 1975|publisher=Lawrence Livermore Laboratory |doi=10.2172/4010212 |osti = 4010212}}</ref>]]
[[File:Chalkogene.jpg|thumb|left|The four stable chalcogens at [[Standard temperature and pressure|STP]]]]
[[File:Phase diagram of solid oxygen.svg|thumb|[[Phase diagram]] for [[solid oxygen]]]]

Oxygen's most common [[allotrope]] is diatomic oxygen, or O<sub>2</sub>, a reactive paramagnetic molecule that is ubiquitous to [[aerobic organism]]s and has a blue color in its [[liquid oxygen|liquid state]]. Another allotrope is O<sub>3</sub>, or [[ozone]], which is three oxygen atoms bonded together in a bent formation. There is also an allotrope called [[tetraoxygen]], or O<sub>4</sub>,<ref>{{cite journal|title = The ε Phase of Solid Oxygen: Evidence of an O4 Molecule Lattice|year = 1999|bibcode = 1999PhRvL..83.4093G|last1 = Gorelli|first1 = Federico A.|last2 = Ulivi|first2 = Lorenzo|last3 = Santoro|first3 = Mario|last4 = Bini|first4 = Roberto|volume = 83|page = 4093|journal = Physical Review Letters|doi = 10.1103/PhysRevLett.83.4093|issue = 20}}</ref> and six allotropes of [[solid oxygen]] including "red oxygen", which has the formula O<sub>8</sub>.<ref>{{cite journal|title = Observation of an O8 molecular lattice in the ε phase of solid oxygen|doi=10.1038/nature05174|journal =Nature|volume =443|issue =7108|pages =201–4|pmid =16971946|year = 2006|last1 = Lundegaard|first1 = Lars F.|last2 = Weck|first2 = Gunnar|last3 = McMahon|first3 = Malcolm I.|last4 = Desgreniers|first4 = Serge|last5 = Loubeyre|first5 = Paul|bibcode = 2006Natur.443..201L|s2cid=4384225}}</ref>

Sulfur has over 20 known allotropes, which is more than any other element except [[allotropes of carbon|carbon]].<ref name="Greenwood">{{Greenwood&Earnshaw|pages = 645–662}}</ref> 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 include [[rhombic crystal system|rhombic]] sulfur and [[monoclinic]] 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&nbsp;°C, the chains begin to break down. If liquid sulfur above 190&nbsp;°C is [[freezing|frozen]] very rapidly, the resulting sulfur is amorphous or "plastic" sulfur. Gaseous sulfur is a mixture of diatomic sulfur (S<sub>2</sub>) and 8-atom rings.<ref>{{cite web|last = McClure|first = Mark R.|url = http://www.uncp.edu/home/mcclurem/ptable/sulfur/s.htm|title = sulfur|access-date = November 25, 2013|archive-url = https://web.archive.org/web/20140312220122/http://www2.uncp.edu/home/mcclurem/ptable/sulfur/s.htm|archive-date = March 12, 2014|url-status = dead|df = mdy-all}}</ref>

Selenium has at least eight distinct allotropes.<ref>{{Greenwood&Earnshaw2nd|page=751}}</ref> The gray allotrope, commonly referred to as the "metallic" allotrope, despite not being a metal, is stable and has a hexagonal [[crystal structure]]. The gray allotrope of selenium is soft, with a [[Mohs hardness]] of 2, and brittle. Four other allotropes of selenium are [[metastable]]. These include two [[monoclinic]] red allotropes and two [[amorphous]] allotropes, one of which is red and one of which is black.<ref>{{Cite web|vauthors = Butterman WC, ((Brown RD Jr)) |url =http://pubs.usgs.gov/of/2003/of03-018/of03-018.pdf |title = Selenium. Mineral Commodity Profiles|year = 2004 |publisher = Department of the Interior |url-status=live |archive-url=https://web.archive.org/web/20121003211018/http://pubs.usgs.gov/of/2003/of03-018/of03-018.pdf |archive-date=October 3, 2012 |access-date=November 25, 2013}}</ref> The red allotrope converts to the black allotrope in the presence of heat. The gray allotrope of selenium is made from [[spiral]]s on selenium atoms, while one of the red allotropes is made of stacks of selenium rings (Se<sub>8</sub>).<ref name="ReferenceB"/>{{dubious|date=September 2014}}

Tellurium is not known to have any allotropes,<ref>{{cite web |last = Emsley |first = John |url = http://www.rsc.org/periodic-table/element/52/tellurium |title = Tellurium |year = 2011 |access-date=November 25, 2013 |publisher=Royal Society of Chemistry}}</ref> although its typical form is hexagonal. Polonium has two allotropes, which are known as α-polonium and β-polonium.<ref>{{cite web|last = Emsley|first = John|url =http://www.rsc.org/periodic-table/element/84/polonium|title = Polonium|year = 2011 |access-date=November 25, 2013 |publisher=Royal Society of Chemistry}}</ref> α-polonium has a cubic crystal structure and converts to the rhombohedral β-polonium at 36&nbsp;°C.<ref name="ReferenceB"/>

The chalcogens have varying crystal structures. Oxygen's crystal structure is [[monoclinic crystal system|monoclinic]], sulfur's is [[orthorhombic crystal system|orthorhombic]], selenium and tellurium have the [[hexagonal crystal system|hexagonal]] crystal structure, while polonium has a [[cubic crystal system|cubic crystal structure]].<ref name="Jackson2002" /><ref name="The Elements">{{cite book|last = Gray|first = Theodore|title = The Elements|year = 2011|publisher = Black Bay and Leventhal publishers}}</ref>
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===Chemical===

Oxygen, sulfur, and selenium are [[Nonmetal (chemistry)|nonmetal]]s, and tellurium is a [[metalloid]], meaning that its chemical properties are between those of a [[metal]] and those of a nonmetal.<ref name="The Elements"/> It is not certain whether polonium is a metal or a metalloid. Some sources refer to polonium as a metalloid,<ref name="ReferenceB"/><ref name="Chemistry & reactivity">{{cite book|author1=Kotz, John C. |author2=Treichel, Paul M. |author3=Townsend, John Raymond |url = https://books.google.com/books?id=jcn6sgt7RpoC&pg=PA65 |title = Chemistry & Chemical Reactivity|year = 2009|page=65|publisher=Cengage Learning|isbn=978-0-495-38703-9}}</ref> although it has some metallic properties. Also, some allotropes of selenium display characteristics of a metalloid,<ref>{{cite web |url=http://www.gordonengland.co.uk/elements/metaloids.htm |title=Periodic Table of the Elements – Metalloids |publisher=Gordonengland.co.uk |access-date=November 25, 2013}}</ref> 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 vacant [[d-orbital]]s. Oxygen's electronegativity is also much higher than those of the other chalcogens. This makes oxygen's [[electric polarizability]] several times lower than those of the other chalcogens.<ref name="synth">{{cite book |author = Zakai, Uzma I. |url = https://books.google.com/books?id=k-LjiXfTXnYC |title = Design, Synthesis, and Evaluation of Chalcogen Interactions |year = 2007 |isbn = 978-0-549-34696-8 |access-date = November 25, 2013 }}{{Dead link|date=November 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

For [[covalent bond]]ing a chalcogen may accept two electrons according to the [[octet rule]], leaving two [[lone pair]]s. When an atom forms two [[single bond]]s, they [[bent molecular geometry|form an angle between 90° and 120°]]. In 1+ [[cation]]s, such as [[hydroxonium|{{chem2|H3O+}}]], a chalcogen forms three [[molecular orbital]]s arranged in a [[trigonal pyramidal molecular geometry|trigonal pyramidal]] fashion and one lone pair. Double bonds are also common in chalcogen compounds, for example in chalcogenates (see below).

The [[oxidation 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.<ref name="wisc"/> Other oxidation numbers, such as −1 in [[pyrite]] and [[peroxide]], do occur. The highest formal [[oxidation number]] is +6.<ref name="Jackson2002" /> This oxidation number is found in [[sulfate]]s, [[selenate]]s, [[tellurate]]s, polonates, and their corresponding acids, such as [[sulfuric acid]].

Oxygen is the most [[electronegative]] element except for [[fluorine]], and forms compounds with almost all of the chemical elements, including some of the [[noble gas]]es. It commonly bonds with many metals and [[metalloids]] to form [[oxide]]s, including [[iron oxide]], [[titanium oxide]], and [[silicon oxide]]. Oxygen's most common [[oxidation state]] is −2, and the oxidation state −1 is also relatively common.<ref name="Jackson2002" /> With [[hydrogen]] it forms water and [[hydrogen peroxide]]. Organic oxygen compounds are ubiquitous in [[organic chemistry]]. <!--the text is broken apart too much, they're having five stories and not one-->

Sulfur's oxidation states are −2, +2, +4, and +6. Sulfur-containing analogs of oxygen compounds often have the prefix ''thio-''. Sulfur's chemistry is similar to oxygen's, in many ways. One difference is that sulfur-sulfur [[double bond]]s are far weaker than oxygen-oxygen double bonds, but sulfur-sulfur [[single bond]]s are stronger than oxygen-oxygen single bonds.<ref>{{cite web|url = http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch10/group6.php#selenium|title = The Chemistry of Oxygen and Sulfur |access-date=November 25, 2013 |publisher = Bodner Research Web}}</ref> Organic sulfur compounds such as [[thiol]]s have a strong specific smell, and a few are utilized by some organisms.<ref name="ReferenceB"/>

Selenium's oxidation states are −2, +4, and +6. Selenium, like most chalcogens, bonds with oxygen.<ref name="ReferenceB"/> There are some [[organoselenium chemistry|organic selenium compounds]], such as [[selenoproteins]]. Tellurium's oxidation states are −2, +2, +4, and +6.<ref name="Jackson2002" /> Tellurium forms the oxides [[tellurium monoxide]], [[tellurium dioxide]], and [[tellurium trioxide]].<ref name="ReferenceB"/> Polonium's oxidation states are +2 and +4.<ref name="Jackson2002" />
[[File:Brindis (24675281395).jpg|thumb|upright|left|[[Water]] ({{chem2|H2O}}) is the most familiar chalcogen-containing compound.|alt=Water dripping into a glass, showing drops and bubbles.]]

There are many acids containing chalcogens, including sulfuric acid, [[sulfurous acid]], [[selenic acid]], and [[telluric acid]]. All [[hydrogen chalcogenide]]s are toxic except for [[water]].<ref name="Emsley2011">{{cite book |last=Emsley |first=John|title=Nature's Building Blocks: An A-Z Guide to the Elements|edition=New|year=2011|publisher=Oxford University Press|location=New York, NY|isbn=978-0-19-960563-7|pages=375–383, 412–415, 475–481, 511–520, 529–533, 582}}</ref><ref>{{cite web |last1 = Van Vleet|first1 = JF|last2=Boon |first2=GD |last3=Ferrans |first3=VJ|url = http://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+7057|title = Tellurium compounds|year = 1981|publisher=The Toxicology and Environmental Health Information Program, US National Institutes of Health |access-date=November 25, 2013}}</ref> Oxygen ions often come in the forms of [[oxide]] ions ({{chem2|O(2-)}}), [[peroxide]] ions ({{chem2|O2(2-)}}), and [[hydroxide]] ions ({{chem2|OH-}}). Sulfur ions generally come in the form of [[sulfide]]s ({{chem2|S(2-)}}), [[bisulfide]]s ({{chem2|SH-}}), [[sulfite]]s ({{chem2|SO3(2-)}}), [[sulfate]]s ({{chem2|SO4(2-)}}), and [[thiosulfate]]s ({{chem2|S2O3(2-)}}). Selenium ions usually come in the form of [[selenide]]s ({{chem2|Se(2-)}}), [[selenite (ion)|selenite]]s ({{chem2|SeO3(2-)}}) and [[selenate]]s ({{chem2|SeO4(2-)}}). Tellurium ions often come in the form of [[tellurate]]s ({{chem2|TeO4(2-)}}).<ref name="Jackson2002" /> Molecules containing metal bonded to chalcogens are common as minerals. For example, [[pyrite]] (FeS<sub>2</sub>) is an [[iron ore]], and the rare mineral [[calaverite]] is the ditelluride {{chem2|([[Au]], [[Ag]])Te2}}.

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 [[chalcogenide]]s. The term ''chalcogenide'' is more commonly reserved for [[sulfide]]s, [[selenide]]s, and [[telluride (chemistry)|telluride]]s, rather than for [[oxide]]s<!--then why are you talking about oxygen here at all?-->.<ref name="chalcogen2" /><ref name='handbook'>{{cite book |url=https://books.google.com/books?id=IvGnUAaSqOsC&pg=PT24 |editor1=Devillanova, Francesco |title=Handbook of Chalcogen Chemistry –New Perspectives in Sulfur, Selenium and Tellurium |publisher=Royal Society of Chemistry |year=2007 |isbn=978-0-85404-366-8 |access-date=November 25, 2013}}</ref><ref name='Takahisa'>{{cite journal|doi=10.1016/0039-6028(91)90679-M|title=Passivation of GaAs(001) surfaces by chalcogen atoms (S, Se and Te)|year=1991|last1=Takahisa|first1=Ohno|journal=Surface Science|volume=255|issue=3|page=229|bibcode = 1991SurSc.255..229T }}</ref>

Except for polonium, the chalcogens are all fairly similar to each other chemically. They all form X<sup>2−</sup> ions when reacting with [[electropositive]] metals.<ref name="wisc">{{cite web|url=http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Group-VIA-Chalcogens-609.html |title=Group VIA: Chalcogens |publisher=Chemed.chem.wisc.edu |url-status=dead |access-date=November 25, 2013 |archive-url=https://web.archive.org/web/20131104164205/http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Group-VIA-Chalcogens-609.html |archive-date=November 4, 2013 }}</ref>

[[Sulfide mineral]]s and analogous compounds produce gases upon reaction with oxygen.<ref>{{cite journal |url=http://www.minersoc.org/pages/Archive-MM/Volume_57/57-389-599.pdf |archive-url=https://web.archive.org/web/20131029185906/http://www.minersoc.org/pages/Archive-MM/Volume_57/57-389-599.pdf |archive-date=2013-10-29 |url-status=live |title=Mineral deposits and chalcogen gases |author=Hale, Martin |journal=Mineralogical Magazine |year=1993 |volume=57 |pages=599–606|doi=10.1180/minmag.1993.057.389.04|issue=389 |access-date=November 25, 2013|bibcode=1993MinM...57..599H|citeseerx=10.1.1.606.8357 }}</ref>
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