Editing Arsenic (section)

== Characteristics ==

=== Physical characteristics ===
{{main|Allotropes of arsenic}}
[[File:SbAs lattice.png|thumb|left|Crystal structure common to [[antimony|Sb]], [[Stibarsen|AsSb]] and grey As]]
[[File:Arsenic nodule.jpg|thumb|left|Gray arsenic nodule]]
The three most common arsenic [[Allotropy|allotropes]] are grey, yellow, and black arsenic, with grey being the most common.<ref name="Norman">{{cite book|title = Chemistry of Arsenic, Antimony and Bismuth|first = Nicholas C.|last = Norman|publisher = Springer|date = 1998|isbn = 978-0-7514-0389-3|url = https://books.google.com/books?id=vVhpurkfeN4C|page = 50}}</ref> Grey arsenic (α-As, [[space group]] R{{overline|3}}m No. 166) adopts a double-layered structure consisting of many interlocked, ruffled, six-membered rings. Because of weak bonding between the layers, grey arsenic is brittle and has a relatively low [[Mohs hardness]] of 3.5. Nearest and next-nearest neighbors form a distorted octahedral complex, with the three atoms in the same double-layer being slightly closer than the three atoms in the next.<ref name="Wiberg2001">{{cite book|last1 = Wiberg|first1 = Egon|last2 = Wiberg|first2 = Nils|last3 = Holleman|first3 = Arnold Frederick|title = Inorganic Chemistry|publisher = Academic Press|date = 2001|isbn = 978-0-12-352651-9}}</ref> This relatively close packing leads to a high density of 5.73&nbsp;g/cm<sup>3</sup>.<ref name="Holl" /> Grey arsenic is a [[semimetal]], but becomes a [[semiconductor]] with a [[bandgap]] of 1.2–1.4&nbsp;eV if [[wikt: amorphized|amorphized]].<ref>{{cite book|author=Madelung, Otfried |title=Semiconductors: data handbook|url=https://books.google.com/books?id=v_8sMfNAcA4C&pg=PA410|date=2004|publisher=Birkhäuser|isbn=978-3-540-40488-0|pages=410–}}</ref> Grey arsenic is also the most stable form.
Yellow arsenic is soft and waxy, and somewhat similar to [[tetraphosphorus]] ({{chem2|P4}}).<ref>{{cite journal |last1=Seidl |first1=Michael |last2=Balázs |first2=Gábor |last3=Scheer |first3=Manfred |title=The Chemistry of Yellow Arsenic |journal=Chemical Reviews |volume=119 |issue=14 |pages=8406–8434 |date=22 March 2019 |doi=10.1021/acs.chemrev.8b00713|pmid=30900440 |s2cid=85448636 }}</ref> Both have four atoms arranged in a [[tetrahedral]] structure in which each atom is bound to each of the other three atoms by a single bond. This unstable allotrope, being molecular, is the most volatile, least dense, and most toxic. Solid yellow arsenic is produced by rapid cooling of arsenic vapor, {{chem2|As4}}. It is rapidly transformed into grey arsenic by light. The yellow form has a density of 1.97&nbsp;g/cm<sup>3</sup>.<ref name="Holl" /> Black arsenic is similar in structure to [[black phosphorus]].<ref name="Holl" /><!--10.1002/jlac.18440490302 Ueber Allotropie bei einfachen Körpern, als eine der Ursachen der Isomerie bei ihren Verbindungen (pp. 247–264)
Jac. Berzelius Volume 49 Issue 3, Pages 247–366 (1844) Justus Liebigs Annalen der Chemie
10.1002/jlac.18671440115
10.1002/jlac.19134000206
10.1002/zaac.19020320158
10.1002/zaac.18940060139
10.1002/cber.19080410197
10.1002/zaac.18940060139
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Black arsenic can also be formed by cooling vapor at around 100–220&nbsp;°C and by crystallization of amorphous arsenic in the presence of mercury vapors.<ref>{{Cite journal|last1=Antonatos|first1=Nikolas|last2=Luxa|first2=Jan|last3=Sturala|first3=Jiri|last4=Sofer|first4=Zdeněk|date=2020|title=Black arsenic: a new synthetic method by catalytic crystallization of arsenic glass|journal=Nanoscale|volume=12|issue=9|language=en|pages=5397–5401|doi=10.1039/C9NR09627B|pmid=31894222|s2cid=209544160}}</ref> It is glassy and brittle. Black arsenic is also a poor electrical conductor.<ref>[http://www.chemicool.com/elements/arsenic.html Arsenic Element Facts]. chemicool.com</ref>

Arsenic [[Sublimation (phase transition)|sublimes]] upon heating at [[atmospheric pressure]], converting directly to a gaseous form without an intervening liquid state at {{convert|887|K|C}}. The [[triple point]] is at 3.63&nbsp;MPa and {{convert|1090|K|C}}.<ref name="Holl" /><ref name="Gokcen1989" />

=== Isotopes ===
{{Main|Isotopes of arsenic}}

Arsenic occurs in nature as one stable [[isotope]], <sup>75</sup>As, and is therefore called a [[monoisotopic element]].<ref name="NUBASE">{{NUBASE 2003}}</ref> As of 2024, at least 32 [[radioisotope]]s have also been synthesized, ranging in [[atomic mass]] from 64 to 95.<ref>{{NUBASE 2020}}</ref><ref name="shimizu2024">{{cite journal |last1=Shimizu |first1=Y. |last2=Kubo |first2=T. |last3=Sumikama |first3=T. |last4=Fukuda |first4=N. |last5=Takeda |first5=H. |last6=Suzuki |first6=H. |last7=Ahn |first7=D.S. |last8=Inabe |first8=N. |last9=Kusaka |first9=K. |last10=Ohtake |first10=M. |last11=Yanagisawa |first11=Y. |last12=Yoshida |first12=K. |last13=Ichikawa |first13=Y. |last14=Isobe |first14=T. |last15=Otsu |first15=H. |last16=Sato |first16=H. |last17=Sonoda |first17=T. |last18=Murai |first18=D. |last19=Iwasa |first19=N. |last20=Imai |first20=N. |last21=Hirayama |first21=Y. |last22=Jeong |first22=S.C. |last23=Kimura |first23=S. |last24=Miyatake |first24=H. |last25=Mukai |first25=M. |last26=Kim |first26=D.G. |last27=Kim |first27=E. |last28=Yagi |first28=A. |display-authors=6 |title=Production of new neutron-rich isotopes near the N = 60 isotones Ge 92 and As 93 by in-flight fission of a 345 MeV/nucleon U 238 beam |journal=Physical Review C |date=8 April 2024 |volume=109 |issue=4 |page=044313 |doi=10.1103/PhysRevC.109.044313}}</ref> The most stable of these is <sup>73</sup>As with a [[half-life]] of 80.30&nbsp;days. The majority of the other isotopes have half-lives of under one day, with the exceptions being
{{div col begin|colwidth=15em}}
: <sup>71</sup>As ({{mvar|t}}<sub>{{small|½}}</sub> {{=}} 65.30&nbsp;hours),
: <sup>72</sup>As ({{mvar|t}}<sub>{{small|½}}</sub> {{=}} 26.0&nbsp;&nbsp;hours),
: <sup>74</sup>As ({{mvar|t}}<sub>{{small|½}}</sub> {{=}} 17.77&nbsp;days),
: <sup>76</sup>As ({{mvar|t}}<sub>{{small|½}}</sub> {{=}} 26.26&nbsp;hours),
: <sup>77</sup>As ({{mvar|t}}<sub>{{small|½}}</sub> {{=}} 38.83&nbsp;hours).
{{div col end}}
Isotopes that are lighter than the stable <sup>75</sup>As tend to decay by [[beta decay|β<sup>+</sup> decay]], and those that are heavier tend to decay by [[beta decay|β<sup>−</sup> decay]], with some exceptions.

At least 10&nbsp;[[nuclear isomer]]s have been described, ranging in atomic mass from 66 to 84. The most stable of arsenic's isomers is <sup>68m</sup>As with a half-life of 111&nbsp;seconds.<ref name="NUBASE" />

=== Chemistry ===

Arsenic has a similar [[electronegativity]] and [[ionization energies]] to its lighter [[pnictogen]] [[Congener (chemistry)|congener]] phosphorus and therefore readily forms [[covalent]] molecules with most of the [[nonmetals]]. Though stable in dry air, arsenic forms a golden-bronze [[tarnish]] upon exposure to humidity which eventually becomes a black surface layer.<ref name="Greenwood552">Greenwood and Earnshaw, pp. 552–4</ref> When heated in air, arsenic [[oxidation|oxidizes]] to [[arsenic trioxide]]; the fumes from this reaction have an odor resembling garlic. This odor can be detected on striking [[arsenide]] minerals such as [[arsenopyrite]] with a hammer.<ref name="Gokcen1989" /> It burns in oxygen to form arsenic trioxide and [[arsenic pentoxide]], which have the same structure as the more well-known phosphorus compounds, and in fluorine to give [[arsenic pentafluoride]].<ref name="Greenwood552" /> Arsenic makes [[arsenic acid]] with concentrated [[nitric acid]], [[arsenous acid]] with dilute nitric acid, and [[arsenic trioxide]] with concentrated [[sulfuric acid]]; however, it does not react with water, alkalis, or non-oxidising acids.<ref>{{cite EB1911|wstitle=Arsenic |volume=2 |pages=651–654}}</ref> Arsenic reacts with metals to form [[arsenide]]s, though these are not ionic compounds containing the As<sup>3−</sup> ion as the formation of such an anion would be highly endothermic and even the group 1 arsenides have properties of [[intermetallic]] compounds.<ref name="Greenwood552" /> Like [[germanium]], [[selenium]], and [[bromine]], which like arsenic [[d-block contraction|succeed the 3d transition series]], arsenic is much less stable in the +5 [[oxidation state]] than its vertical neighbors phosphorus and [[antimony]], and hence arsenic pentoxide and arsenic acid are potent [[oxidizers]].<ref name="Greenwood552" />