Name: Indium
Symbol: In
Atomic Number: 49
Atomic Weight: 114.818000
Family: Boron Family
CAS RN: 7440-74-6
Description: Rare silver-white metal with one of the longest liquid range of all the elements.
State (25C): Solid
Oxidation states: +3

Molar Volume: 15.73 cm3/mole
Valence Electrons: 5p1

Boiling Point:  2346K, 2073C, 3763F
Melting Point:
429.91K, 156.76C, 314.17F
Electrons Energy Level: 2, 8, 18, 18, 3
Isotopes: 35 + 1 Stable
Heat of Vaporization: 231.5 kJ/mol
Heat of Fusion: 263 kJ/mol
Density: 7.31 g/cm3 @ 300K
Specific Heat: 0.23 J/gK
Atomic Radius: 2
Ionic Radius: 0.8
Electronegativity: 1.78 (Pauling); 1.49 (Allrod Rochow)
Vapor Pressure: 1.42E+17 Pa @ 156.76C
Indium (named from the Latin indicum, for the color indigo in its atomic spectrum) was discovered by German chemists Ferdinand Reich and  Hieronymus Theodor Richter in 1863 while they were testing Zinc ores with a spectrograph in search of Thallium.  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.  It is interesting to note that most elements were discovered while searching for other elements.  Curiously enough, Reich who did the initial chemical isolation work was color blind and had to turn over his experiment to his assistant (Richter) who was the first to observe the characteristic lines.  Richter went on to isolate the metal in 1867.

This rare, soft, malleable and easily fusible poor metal, is chemically similar to Aluminum or Gallium but looks more like Zinc (Zinc ores are also the primary source of this metal).  Its current primary application is to form transparent electrodes from Indium Tin Oxide in liquid crystal displays (LCDs).  It is widely used in thin-films to form lubricated layers (during World War II it was widely used to coat bearings in high-performance aircraft).  It's also used for making particularly low melting point alloys, and is a component in some lead-free solders.

It is generally found in deposits with zinc and refineries which produce this more common metal often sell indium as well. The pure metal is so soft that you can "wipe" it onto other materials in much the same way as lead (or even pencil graphite). It is corrosion resistant.


1s2 2s2p6 3s2p6d10 4s2p6d10 5s2p1


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 4.411014 years.  Also, Indium is not a notorious cumulative poison, like its neighbor Cadmium, and is relatively rare.

2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10
5s2 5p1


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;


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.


Indium Oxide, In2O3 Trimethylindium
Indium Antimonide Indium Phosphide
Indium Nitride Indium Tin Oxide


atom.gif (700 bytes)

Isotope Atomic Mass Half-Life
In98 97.942 >1.5 us
In99 98.935  
In100 99.931 7 seconds
In101 100.927 15.1 seconds
In102 101.925 22 seconds
In103 102.9199 65 seconds
In104 103.918 1.8 minutes
In105 104.9147 5.07 minutes
In106 105.9135 6.2 minutes
In107 106.9103 32.4 minutes
In108 107.9097 58 minutes
In109 108.9072 4.2 hours
In110 109.9072 4.9 hours
In111 110.9051 2.8047 days
In112 111.9055 14.97 minutes
In113 112.9041 Stable
In114 113.9049 71.9 seconds
In115 114.9039 4.41E 14 years
In116 115.9053 14.1 seconds
In117 116.9045 43.2 minutes
In118 117.9064 5 seconds
In119 118.9059 2.4 minutes
In120 119.908 3.08 seconds
In121 120.9078 23.1 seconds
In122 121.9103 1.5 seconds
In123 122.9104 5.98 seconds
In124 123.9132 3.11 seconds
In125 124.9136 2.36 seconds
In126 125.9165 1.6 seconds
In127 126.9173 1.09 seconds
In128 127.9202 0.84 seconds
In129 128.922 0.61 seconds
In130 129.9249 0.32 seconds
In131 130.9268 0.282 seconds
In132 131.9329 0.201 seconds
In133 132.938 180 ms
In134 133.945 138 ms


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."

40px-Skull_and_crossbones.svg.jpg (1420 bytes) For example, Indium Trichloride anhydrous (InCl3) is quite toxic, while Indium Phosphide (InP) is both toxic and a suspected carcinogen.

atom.gif (700 bytes)

Indium Data

Atomic Radius (): 2
Atomic Volume cm3/mol : 15.7cm3/mol
Covalent Radius: 1.44
Crystal Structure: Tetragonal
Ionic Radius: 0.8

Chemical Properties

Electrochemical Equivalents: 1.428 g/amp-hr
Electron Work Function: 4.12eV
Electronegativity: 1.78 (Pauling); 1.49 (Allrod Rochow)
Heat of Fusion: 263 kJ/mol
Incompatibilities: (Dinitrogen Tetraoxide + Acetonitrile), Mercury (II) Bromide (at 662F), Sulfur (mixtures ignite when heated)
First Ionization Potential: 5.786
Second Ionization Potential: 18.869
Third Ionization Potential: 28.03
Valence Electron Potential(-eV): 54
Ionization Energy (eV): 5.786 eV

Physical Properties

Atomic Mass Average: 114.818
Boiling Point: 2346K, 2073C, 3763F
Melting Point: 429.91K, 156.76C, 314.17F
Heat of Vaporization: 231.5 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 33E-6
Electrical Conductivity: 0.116 106/cm
Thermal Conductivity: 0.816 W/cmK
Density: 7.31 g/cm3 @ 300K
Enthalpy of Atomization: 242.7 kJ/mole @ 25C
Enthalpy of Fusion: 3.28 kJ/mole
Enthalpy of Vaporization: 226.4 kJ/mole
Flammability Class: Non-Combustible Solid (except as dust)
Molar Volume: 15.73 cm3/mole
Optical Reflectivity: unknown
Optical Refractive Index: unknown
Relative Gas Density (Air=1): unknown
Specific Heat: 0.23 J/gK
Vapor Pressure: 1.42E+17 Pa @ 156.76C
Estimated Crustal Abundance: 2.510-1 milligrams per kilogram
Estimated Oceanic Abundance: 210-2 milligrams per liter

(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