Thallium (indium's heavier homolog) shows an even stronger effect, causing oxidation to thallium(I) to be more probable than to thallium(III), whereas gallium (indium's lighter homolog) commonly shows only the +3 oxidation state. The stabilization of the monovalent state is attributed to the inert pair effect, in which relativistic effects stabilize the 5s-orbital, observed in heavier elements. In some cases, the pair of 5s-electrons are not donated, resulting in indium(I), In +. In compounds, indium most commonly donates the three outermost electrons to become indium(III), In 3+. Indium has 49 electrons, with an electronic configuration of 4d 105s 25p 1. However it does have a size effect in bending and indentation, associated to a length-scale of order 50–100 µm, significantly large when compared with other metals. Indium displays a ductile viscoplastic response, found to be size-independent in tension and compression. Indium has greater solubility in liquid mercury than any other metal (more than 50 mass percent of indium at 0 ☌). Indium crystallizes in the body-centered tetragonal crystal system in the space group I4/ mmm ( lattice parameters: a = 325 pm, c = 495 pm): this is a slightly distorted face-centered cubic structure, where each indium atom has four neighbours at 324 pm distance and eight neighbours slightly further (336 pm). Below the critical temperature, 3.41 K, indium becomes a superconductor. The density of indium, 7.31 g/cm 3, is also greater than gallium, but lower than thallium. The boiling point is 2072 ☌ (3762 ☏), 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 electrons delocalized. Like both, indium has a low melting point, 156.60 ☌ (313.88 ☏) higher than its lighter homologue, gallium, but lower than its heavier homologue, thallium, and lower than tin. Like gallium, indium is able to wet glass. Like tin, a high-pitched cry is heard when indium is bent – a crackling sound due to crystal twinning. It is a member of group 13 on the periodic table and its properties are mostly intermediate between its vertical neighbors gallium and thallium. It is so soft ( Mohs hardness 1.2) that it can be cut with a knife and leaves a visible line when rubbed on paper. Indium is a silvery-white, highly ductile post-transition metal with a bright luster. Properties Physical Indium wetting the glass surface of a test tube Indium has no biological role and its compounds are toxic when inhaled or injected into the bloodstream, although they are poorly absorbed following ingestion. It is produced exclusively as a by-product during the processing of the ores of other metals, chiefly from sphalerite and other zinc sulfide ores. Indium is also used in the semiconductor industry, in low-melting-point metal alloys such as solders and soft-metal high-vacuum seals. Indium is a technology-critical element used primarily in the production of flat-panel displays as indium tin oxide (ITO), a transparent and conductive coating applied to glass. It was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter by spectroscopic methods and named for the indigo blue line in its spectrum. Chemically, indium is similar to gallium and thallium, and its properties are largely intermediate between the two. It is a silvery-white post-transition metal and one of the softest elements. Indium is a chemical element it has symbol In and atomic number 49.

Iridium metallic