The chemical element indium is classed as an other metal. It was discovered in 1863 by Ferdinand Reich.
|Classification:||Indium is an ‘other metal’|
|Melting point:||156.6 oC, 429.8 K|
|Boiling point:||2070 oC, 2343 K|
|Neutrons in most abundant isotope:||66|
|Electron configuration:||[Kr] 4d10 5s2 5p1|
|Density @ 20oC:||7.31 g/cm3|
|Atomic volume:||15.7 cm3/mol|
|Structure:||tetragonal, distorted fcc structure|
|Specific heat capacity||0.23 J g-1 K-1|
|Heat of fusion||3.263 kJ mol-1|
|Heat of atomization||244 kJ mol-1|
|Heat of vaporization||231.50 kJ mol-1|
|1st ionization energy||558.3 kJ mol-1|
|2nd ionization energy||1820.6 kJ mol-1|
|3rd ionization energy||2704.5 kJ mol-1|
|Electron affinity||39 kJ mol-1|
|Minimum oxidation number||0|
|Min. common oxidation no.||0|
|Maximum oxidation number||3|
|Max. common oxidation no.||3|
|Electronegativity (Pauling Scale)||1.78|
|Polarizability volume||9.7 Å3|
|Reaction with air||mild, w/ht ⇒ In2O3|
|Reaction with 15 M HNO3||mild ⇒ In(NO3)3|
|Reaction with 6 M HCl||mild, ⇒ H2, InCl3|
|Reaction with 6 M NaOH||none|
|Chloride(s)||InCl, InCl2, InCl3|
|Atomic radius||155 pm|
|Ionic radius (1+ ion)||–|
|Ionic radius (2+ ion)||–|
|Ionic radius (3+ ion)||94 pm|
|Ionic radius (1- ion)||–|
|Ionic radius (2- ion)||–|
|Ionic radius (3- ion)||–|
|Thermal conductivity||81.8 W m-1 K-1|
|Electrical conductivity||3.4 x 106 S m-1|
|Freezing/Melting point:||156.6 oC, 429.8 K|
Discovery of Indium
In 1863, Ferdinand Reich discovered indium in Germany. He had intended to investigate whether zinc sulfide ore (sphalerite) also contained thallium. Instead, as a result of his careful observations, he became the discoverer of a new element. (1)
After roasting the ore to remove most of the sulfur, he decomposed the remaining material with hydrochloric acid.
He saw a straw colored solid appear. Reich began to suspect that this straw colored precipitate might be the sulfide of a new element. (2)
He investigated this further by getting an emission spectrum for the sample. Unfortunately for Reich, his color-blindness prevented him from accurately interpreting this for himself.
He asked his countryman, German chemist Hieronymus T. Richter, to look at the flame colors produced. Richter observed a brilliant indigo line, which did not match the spectral line of any known element. (3)
This line enabled Reich and Richter to show that a new element was present in their sample.
The men later isolated the metal by a lengthy series of precipitations and made a thorough study of its properties. The yield of indium was 0.1% from the original zinc sulfide ore. (1)
The element was named after its characteristic spectral line – the ‘indi’ coming from the color indigo.
Indium’s Periodic Table Neighborhood
|Group 12||Group 13||Group 14|
Appearance and Characteristics
Indium is considered to be of low toxicity.
Indium is a very soft, silvery-white lustrous metal.
Indium liquid clings to or wets glass and similar surfaces.
Like gallium, indium remains in a liquid state over a wide range of temperatures.
When present in compounds, indium exists mostly in the oxidation state III.
When heated above its melting point, it burns with a violet flame to the yellow sesquioxide (In2O3).
Uses of Indium
Indium is used in the production of low-melting alloys, typically with gallium.
The melting point depends on the ratio of indium to gallium.
An alloy with 24% indium and 76% gallium, for example, melts at just 16 oC. (4)
This type of alloy can be used as a non-toxic alternative to mercury in some applications.
Compounds of indium are used in the semiconductor industry for germanium transistors, thermistors, rectifiers and photocells.
Indium can be coated on metals and evaporated onto glass, to form mirrors equal to that made with silver but more corrosion resistant.
Indium-tin oxide thin films are used for liquid crystal displays (LCDs).
Abundance and Isotopes
Abundance earth’s crust: 250 parts per billion by weight, 47 parts per billion by moles
Abundance solar system: 4 parts per billion by weight, 40 parts per trillion by moles
Cost, pure: $968 per 100g
Cost, bulk: $54 per 100g
Source: Indium has no minerals or ores with a high concentration of the element. Commercially, indium is extracted as a by-product of zinc refining. It is also extracted from iron, lead, and copper ores.
Isotopes: Indium has 35 isotopes whose half-lives are known, with mass numbers from 100 to 134. Of these, one is stable: 113In. Naturally occurring indium is a mixture of two isotopes: 115In, with a half-life of 4.41 x 1014 years and an abundance of 95.7% and 113In with an abundance of 4.3%.
1. J.W. Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry., 1929, vol v, Longmans, Green and Co., p 387,388.
2. Mary Elvira Weeks, Discovery of the Elements, 2003, Kessinger Publishing, p198.
3. U. Schwarz-Schampera, P.M. Herzig, Indium: Geology, Mineralogy, and Economics, 2002, Springer, p5
4. “A metal alloy that is liquid at room temperature.” Scitoys. 10/21/2009.
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