Editing Chalcogen (section)

===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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