Editing Indium (section)

==Properties==

===Physical===
[[File:Indium wetting glass.jpg|thumb|left|Indium wetting the glass surface of a test tube]]
Indium is a shiny silvery-white, highly [[ductile]] [[post-transition metal]] with a bright [[Lustre (mineralogy)|luster]].<ref name="InProcess">{{cite journal|last=Alfantazi|first=A. M.|date=2003|title=Processing of indium: a review|journal=Minerals Engineering|volume=16|issue=8|pages=687–694|doi=10.1016/S0892-6875(03)00168-7|author2=Moskalyk, R. R.|bibcode=2003MiEng..16..687A }}</ref> It is so soft ([[Mohs hardness]] 1.2) that it can be cut with a knife and leaves a visible line like a pencil when rubbed on paper.<ref name="Binder">{{cite book |last=Binder |first=Harry H. |date=1999 |title=Lexicon der chemischen Elemente |publisher=S. Hirzel Verlag |isbn=978-3-7776-0736-8 |language=de }}</ref> It is a member of [[boron group|group 13]] on the [[periodic table]] and its properties are mostly intermediate between its vertical neighbors [[gallium]] and [[thallium]]. As with [[tin]], a high-pitched [[tin cry|cry]] is heard when indium is bent – a crackling sound due to [[crystal twinning]].<ref name="InProcess" /> Like gallium, indium is able to [[wetting|wet]] glass. Like both, indium has a low [[melting point]], 156.60&nbsp;°C (313.88&nbsp;°F); higher than its lighter homologue, gallium, but lower than its heavier homologue, thallium, and lower than tin.<ref name="Lange">{{cite book |last=Dean |first=John A. |title=Lange's handbook of chemistry |publisher=McGraw-Hill, Inc.|date=523|isbn=978-0-07-016190-0|edition=Fifteenth }}</ref> The boiling point is 2072&nbsp;°C (3762&nbsp;°F), higher than that of thallium, but lower than gallium, conversely to the general trend of melting points, but similarly to the trends down the other post-transition metal groups because of the weakness of the metallic bonding with few [[Delocalized electron|electrons delocalized]].<ref name="Greenwood222">Greenwood and Earnshaw, p. 222</ref>

The density of indium, 7.31&nbsp;g/cm<sup>3</sup>, is also greater than gallium, but lower than thallium. Below the [[critical temperature]], 3.41&nbsp;[[kelvin|K]], indium becomes a [[superconductor]]. Indium crystallizes in the body-centered [[tetragonal crystal system]] in the [[space group]] ''I''4/''mmm'' ([[lattice parameter]]s:&nbsp;''a''&nbsp;=&nbsp;325&nbsp;[[picometer|pm]], ''c''&nbsp;=&nbsp;495&nbsp;pm):<ref name="Lange" /> this is a slightly distorted [[face-centered cubic]] structure, where each indium atom has four neighbours at 324&nbsp;pm distance and eight neighbours slightly further (336&nbsp;pm).<ref name="Greenwood252">Greenwood and Earnshaw, p. 252</ref> Indium has greater solubility in liquid mercury than any other metal (more than 50 mass percent of indium at 0&nbsp;°C).<ref>{{Cite journal|title=Hg-In phase diagram|journal=Journal of Phase Equilibria and Diffusion|volume=33|issue=2|pages=159–160|doi=10.1007/s11669-012-9993-3|year=2012|last1=Okamoto|first1=H.|s2cid=93043767}}</ref> Indium displays a ductile [[Viscoplasticity|viscoplastic]] response, found to be size-independent in tension and compression. However it does have a [[Size effect on structural strength|size effect]] in bending and indentation, associated to a length-scale of order 50–100&nbsp;μm,<ref>{{Cite journal|last1=Iliev|first1=S. P.|last2=Chen|first2=X.|last3=Pathan|first3=M. V.|last4=Tagarielli|first4=V. L.|date=2017-01-23|title=Measurements of the mechanical response of Indium and of its size dependence in bending and indentation|journal=Materials Science and Engineering: A|volume=683|pages=244–251|doi=10.1016/j.msea.2016.12.017|hdl=10044/1/43082|hdl-access=free}}</ref> significantly large when compared with other metals.

===Chemical===
Indium has 49 electrons, with an electronic configuration of &#91;[[krypton|Kr]]&#93;4d{{sup|10}}5s{{sup|2}}5p{{sup|1}}. In compounds, indium most commonly donates the three outermost electrons to become indium(III), In{{sup|3+}}. In some cases, the pair of 5s-electrons are not donated, resulting in indium(I), In{{sup|+}}. The stabilization of the [[valence (chemistry)|monovalent]] state is attributed to the [[inert pair effect]], in which [[relativistic quantum chemistry|relativistic effects]] stabilize the 5s-orbital, observed in heavier elements. Thallium (indium's heavier [[Homologous series|homolog]]) shows an even stronger effect, causing [[Redox|oxidation]] to thallium(I) to be more probable than to thallium(III),<ref>{{cite book|publisher = Walter de Gruyter|date = 1985|edition = 91–100|pages = 892–893|isbn = 978-3-11-007511-3|title = Lehrbuch der Anorganischen Chemie|first = Arnold F.|last = Holleman|author2 = Wiberg, Egon |author3 = Wiberg, Nils|chapter =Thallium|language=de}}</ref> whereas gallium (indium's lighter homolog) commonly shows only the +3 oxidation state. Thus, although thallium(III) is a moderately strong [[oxidizing agent]], indium(III) is not, and many indium(I) compounds are powerful [[reducing agent]]s.<ref name="G&E">{{Greenwood&Earnshaw2nd}}</ref> While the energy required to include the s-electrons in chemical bonding is lowest for indium among the group 13 metals, bond energies decrease down the group so that by indium, the energy released in forming two additional bonds and attaining the +3 state is not always enough to outweigh the energy needed to involve the 5s-electrons.<ref name="Greenwood256">Greenwood and Earnshaw, p. 256</ref> Indium(I) oxide and hydroxide are more basic and indium(III) oxide and hydroxide are more acidic.<ref name="Greenwood256" />

A number of standard electrode potentials, depending on the reaction under study,<ref>{{RubberBible92nd|page=8.20}}</ref> are reported for indium, reflecting the decreased stability of the +3 oxidation state:<ref name="Greenwood252" />
:{|
|-
| In<sup>2+</sup> + e<sup>−</sup>|| ⇌ In<sup>+</sup> || E<sup>0</sup> = −0.40 V
|-
| In<sup>3+</sup> + e<sup>−</sup>|| ⇌ In<sup>2+</sup> || E<sup>0</sup> = −0.49 V
|-
| In<sup>3+</sup> + 2 e<sup>−</sup>|| ⇌ In<sup>+</sup> || E<sup>0</sup> = −0.443 V
|-
| In<sup>3+</sup> + 3 e<sup>−</sup>|| ⇌ In || E<sup>0</sup> = −0.3382 V
|-
| In<sup>+</sup> + e<sup>−</sup>|| ⇌ In || E<sup>0</sup> = −0.14 V
|}

Indium metal does not react with water, but it is oxidized by stronger oxidizing agents such as [[halogen]]s to give indium(III) compounds. It does not form a [[boride]], [[silicide]], or [[carbide]], and the hydride [[Indium trihydride|InH<sub>3</sub>]] has at best a transitory existence in [[ether]]eal solutions at low temperatures, being unstable enough to spontaneously polymerize without coordination.<ref name="G&E" /> Indium is rather basic in aqueous solution, showing only slight [[amphoteric]] characteristics, and unlike its lighter homologs aluminium and gallium, it is insoluble in aqueous alkaline solutions.<ref name="Greenwood255">Greenwood and Earnshaw, p. 255</ref>

===Isotopes===
{{Main|Isotopes of indium}}
Indium has 39 known [[isotope]]s, ranging in [[mass number]] from 97 to 135. Only two isotopes occur naturally as [[primordial nuclide]]s: indium-113, the only [[stable isotope]], and indium-115, which has a [[half-life]] of 4.41{{e|14}} years, four orders of magnitude greater than the [[age of the Universe]] and nearly 30,000 times greater than half life of [[thorium-232]].<ref name="Audi">{{NUBASE 2003}}</ref> The half-life of <sup>115</sup>In is very long because the [[beta decay]] to <sup>115</sup>[[tin|Sn]] is [[selection rule|spin-forbidden]].<ref>{{cite journal |last1=Dvornický |first1=R. |last2=Šimkovic |first2=F. |date=13–16 June 2011 |title=Second unique forbidden β decay of <sup>115</sup>In and neutrino mass |journal=AIP Conf. Proc. |volume=1417 |issue=33 |page=33 |doi=10.1063/1.3671032|series=AIP Conference Proceedings |bibcode=2011AIPC.1417...33D }}</ref> Indium-115 makes up 95.7% of all indium. Indium is one of three known elements (the others being [[tellurium]] and [[rhenium]]) of which the stable isotope is less abundant in nature than the long-lived primordial radioisotopes.<ref>{{cite web |url=http://www.ciaaw.org/pubs/Periodic_Table_Isotopes.pdf |title=IUPAC Periodic Table of the Isotopes |date=1 October 2013 |website=ciaaw.org |publisher=[[IUPAC]] |access-date=21 June 2016 |archive-date=14 February 2019 |archive-url=https://web.archive.org/web/20190214115238/http://www.ciaaw.org/pubs/Periodic_Table_Isotopes.pdf |url-status=live }}</ref>

The stablest [[synthetic radioisotope|artificial]] isotope is [[indium-111]], with a half-life of approximately 2.8&nbsp;days. All other isotopes have half-lives shorter than 5 hours. Indium also has 47 meta states, among which indium-114m1 (half-life about 49.51&nbsp;days) is the most stable, more stable than the ground state of any indium isotope other than the primordial. All decay by [[isomeric transition]]. The indium isotopes lighter than <sup>113</sup>In predominantly decay through [[electron capture]] or [[positron emission]] to form [[cadmium]] isotopes, while the indium isotopes heavier than <sup>113</sup>In predominantly decay through beta-minus decay to form tin isotopes.<ref name="Audi" />