1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶d¹⁰ 5s²p¹

Characteristics

Indium is a very soft, silvery-white true metal that has a bright luster.  As a pure metal Indium emits a high-pitched "cry" when it is bent.  Both Gallium and Indium are able to wet glass.

One unusual property of Indium is that its most common isotope is very slightly radioactive; it very slowly decays by beta emission to Tin over time.  This radioactivity is not considered hazardous, mainly because its decay rate is nearly 50,000 times slower than that of natural thorium, with a half-life of 4.41×10¹⁴ years.  Also, Indium is not a notorious cumulative poison, like its neighbor Cadmium, and is relatively rare.

Applications

The first large-scale application for Indium was as a coating for bearing in high-performance aircraft engines during World War II.  Afterwards, production gradually increased as new uses were found in fusible alloys, solders, and elctronics.   In the middle and late 1980s, the development of Indium Phosphide semiconductors and Indium Tin Oxide thin films for liquid crystal displays (LCD) aroused much interest.   By 1992, the thin-film application had become the largest end use. Other uses;

• Used in the manufacture of low-melting-temperature alloys.  An alloy consisting of 24% indium and 76% Gallium is liquid at room temperature.
• Some Indium compounds such as Indium Antimonide, Indium Phosphide, and Indium Nitride are semiconductors with useful properties.
• Used in light emitting diodes (LEDs) and Laser Diodes (LDs) based on compound semiconductors that are fabricated by Metalorganic Vapor Phase Epitaxy (MOVPE) technology.
• The ultrapure metalorganics of Indium, specifically high purity Trimethylindium (TMI) is used as a precursor in III-V compound semiconductors, while it is also used as the semiconductor dopant in II-VI compound semiconductors.
• Can also be plated onto metals and evaporated onto glass which forms a mirror which is as good as those made with Silver but has higher corrosion resistance.
• Indium Oxide (In₂O₃) is used as a transparent conductive glass substrate in the making of electroluminescent panels.
• Used as a light filter in low pressure Sodium vapor lamps.
• Indium's freezing point of 429.7485°K (156.5985°C) is a defining fixed point on the international temperature scale ITS-90. 
• Sometimes used as a component of nuclear control rods. 
• Very small amounts used in Aluminum alloy sacrificial anodes (for salt water applications) to prevent passivation of the aluminium
• ¹¹¹In is used in medical imaging to monitor the activity of white blood cells.  A blood test is taken from the patient, white cells removed and labelled with the radioactive  ¹¹¹In, then re-injected back into the patient. Gamma imaging will reveal any areas of high white cell activity such as an abscess. 

Occurrence

Indium is produced mainly from residues generated during Zinc ore processing but is also found in Iron, Lead, and Copper ores.  The amount of Indium consumed is largely a function of worldwide LCD production. Increased manufacturing efficiency and recycling (especially in Japan) maintain a balance between demand and supply.  The average indium price for 2005 was $900 per kilogram.  This is unusually high.  Demand increased as the metal is used in LCDs and televisions, and supply decreased when a number of Chinese mining concerns stopped extracting indium from their Zinc tailings.  In 2002, the price was $94/kg.

Up until 1924, there was only about a gram of isolated indium on the planet.  The Earth is estimated to contain about 0.1 ppm of Indium which means it is about as abundant as Silver, although Indium is in fact nearly three times more expensive by weight. Canada is a leading producer of Indium.  The TeckCominco refinery in Trail, BC, is the largest single source, with production of 32,500 kg in 2005, 41,800 kg in 2004 and 36,100 kg in 2003.  Worldwide production is typically over 300 tons per year, but demand has risen rapidly with the increased popularity of LCD computer monitors and televisions.

Compounds

Isotopes

Precautions

Pure indium in metal form is considered non-toxic by most sources.  In the welding and semiconductor industries, where indium exposure is relatively high, there have been no reports of any toxic side-effects.

This may not be the case with indium compounds: there is some unconfirmed evidence that suggests that indium has a low level of toxicity.  Other sources are more definite about indium compounds' toxicity - for example, the WebElements website states that "All indium compounds should be regarded as highly toxic. Indium compounds damage the heart, kidney, and liver, and may be teratogenic."

For example, Indium Trichloride anhydrous (InCl3) is quite toxic, while Indium Phosphide (InP) is both toxic and a suspected carcinogen.

(from the brilliant indigo line in its spectrum) Discovered by Reich and Richter, who later isolated the metal.  Indium is most frequently associated with zinc materials, and it is from these that most commercial indium is now obtained; however, it is also found in iron, lead, and copper ores.  Until 1924, a gram or so constituted the world's supply of this element in isolated form.  It is probably about as abundant as silver.  About 4 million troy ounces of indium are now produced annually in the Free World.  Canada is presently producing more than 1,000,000 troy ounces annually.   The present cost of indium is about $1 to $5/g, depending on quantity and purity.   It is available in ultrapure form.  Indium is a very soft, silvery-white metal with a brilliant luster.  The pure metal gives a high-pitched "cry" when bent. It wets glass, as does gallium.  It has found application in making low-melting allows; an allow of 24% indium - 76% gallium is liquid at room temperature.  It is used in making bearing alloys, germanium transistors, rectifiers, thermistors, and photoconductors.  It can be plated onto metal and evaporated onto glass, forming a mirror as good as that made with silver but with more resistance to atmospheric corrosion. There is evidence that indium has a low order of toxicity; however, care should be taken until further information is available.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond

Indium was discovered by the German chemists Ferdinand Reich and Hieronymus Theodor Richter in 1863. Reich and Richter had been looking for traces of the element thallium in samples of zinc ores. A brilliant indigo line in the sample's spectrum revealed the existence of indium. Indium is about as abundant as silver but is much easier to recover since it typically occurs along with zinc, iron, lead and copper ores.

Indium is used to coat the bearings of high speed motors since it allows for the even distribution of lubricating oil. Indium is used to dope germanium to make transistors.  It is also used to make other electrical components such as rectifiers, thermistors and photoconductors. Indium can be used to make mirrors that are as reflective as silver mirrors but do not tarnish as quickly. Indium is also used to make low melting alloys. An alloy of 24% indium and 76% gallium is a liquid at room temperature.