Editing Indium (section)

===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>