Indium

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MELTING POINT: 156.6°C
BOILING POINT: 2,080°C
DENSITY: 7.31g/cm ³
MOST COMMON IONS: In ³⁺ , In ⁺

Indium is a soft, silver-white metal . It was first isolated in 1863 by German chemists Ferdinand Reich and Hieronymus Theodor Richter. Indium was so named because of an intense blue (indigo) line in its emission spectrum. The element is widely distributed in several ores (often in conjunction with zinc) but in low concentrations, accounting for only 0.05 part per million (ppm) of Earth's crust.

The chemical properties of indium are typical of those of Group 13 of the Periodic Table. Most of indium's oxides, salts, and compounds involve the +3 oxidation state (e.g., In ₂ O ₃ , In[NO ₃ ] _3, and InCl ₃ ); many of these compounds are electron-pair acceptors, forming addition compounds with donor molecules (e.g., InBr ₃ · py, py = pyridine). Neutral, cationic, and anionic complexes are also known. Several interesting compounds are derived from the +1 and +2 oxidation states of the element.

Indium was long regarded as rare and uninteresting, but it has found many interesting applications. Its softness results in its use (alone or in alloys ) as a bearing metal, as a sealant, and in high-temperature solders. The positron-emitting radioactive isotopes ¹¹¹ In and ^113m In are used in medical diagnostic imaging.

Organoindium substances are important, especially for the production of materials by metal-organic chemical vapor-phase deposition (MOCVD). This technique involves the thermal decomposition of mixtures of an organoindium compound and a compound such as phosphine (PH ₃ ), leading to the deposition of ordered layers of InP. The resulting compound can be used in the formation of semiconductors and solid-state optical devices (similar to silicon).

SEE ALSO Inorganic Chemistry .

Dennis G. Tuck

Bibliography

Lide, David R., ed. (2003). The CRC Handbook of Chemistry and Physics, 84th edition. Boca Raton, FL: CRC Press.

Internet Resources

Winter, Mark. "Indium." The University of Sheffield and WebElements Ltd., U.K. Available from http://www.webelements.com .