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Indium,  49In
Indium Disc.jpg
Disc of indium
General properties
Name, symbol Indium, In
Appearance silvery lustrous gray
Indium in the periodic table


Atomic number 49
Standard atomic weight (Ar) 114.818(1)
Group, block , p-block
Period period 5
Electron configuration [Kr] 4d10 5s2 5p1
per shell
2, 8, 18, 18, 3
Physical properties
Phase Solid
Melting point 429.7485 K ​(156.5985 °C, ​313.8773 °F)
Boiling point 2345 K ​(2072 °C, ​3762 °F)
Density near r.t. 7.31 g/cm3
when liquid, at  7.02 g/cm3
Triple point 429.7445 K, ​~1 kPa
Heat of fusion 3.281 kJ/mol
Heat of 231.8 kJ/mol
Molar heat capacity 26.74 J/(mol·K)
Atomic properties
Oxidation states 3, 2, 1, −1, −2, −5 ​(an amphoteric oxide)
Electronegativity Pauling scale: 1.78
energies 1st: 558.3 kJ/mol
2nd: 1820.7 kJ/mol
3rd: 2704 kJ/mol
Atomic radius empirical: 167 pm
Covalent radius 142±5 pm
Van der Waals radius 193 pm
Crystal structure ​tetragonal
Speed of sound thin rod 1215 m/s (at 20 °C)
Thermal expansion 32.1 µm/(m·K) (at 25 °C)
Thermal conductivity 81.8 W/(m·K)
Thermal diffusivity 83.7 mm2/s (at 300 K)
Magnetic ordering Diamagnetic
Young's modulus 11 GPa
Mohs hardness 1.2
Brinell hardness 8.8–10.0 MPa
CAS Registry Number 7440-74-6
Discovery Ferdinand Reich and Hieronymous Theodor Richter (1863)
First isolation Hieronymous Theodor Richter (1867)
· references

Indium is a chemical element with symbol In and atomic number 49. A post-transition metal, indium is used mostly in electronics, for indium tin oxide transparent conductive coatings.



Indicium is fairly resistant to corrosion and the effects of many chemicals. It does not react with elements such as boron, silicon or carbon when heated together, however it will react with halogens or oxalic acid to give their respective salts.

Indium burns in the presence of oxygen with a blue flame at high temperatures to form indium(III) oxide:

4 In + 3 O2 → 2 In2O3

Indium also forms indium(I) compounds, though they are not as characterized as indium(III) ones. The most well known are indium(I) oxide, which is a black compound and indium(I) sulfide. Both are made at high temperatures and have little applications. Indium(I) halides cyclopentadienyl compounds are also known.

Indium also displays an intermediate oxidation state +2, though only the halides are known and important.


Indium is a very soft, silvery-grey, highly ductile, relatively rare post-transition metal with a bright luster. Indium is soft enough to be cut with a knife and is soft enough to leave a visible line on paper. Like tin, indium emits a high-pitched "cry" when it is bent. Indium is able to wet glass when melted, property also observed in gallium. Indium has a low melting point, of 156.60 °C and boils at 2072 °C. Its density at room temperature is 7.31 g/cm3.


Indium is sold by various chemical suppliers, though it's expensive. GalliumSource sells 1 kg of indium at $ 840, while 10 g are available at $ 20.

Certain solders contain small amounts of indium, though extracting it may not be practical.


Indium can be extracted from solders or transparent coatings by dissolving them in acid and then obtained from its salts via either reduction with zinc metal or electrowinning. However, the amount obtained this way is small.


  • Demonstration of metal "cry"
  • Low melting point alloys



Indium does not have any metabolic role in any organism. Due to its position in group 13, its chemical properties are similar to that of aluminium compounds. Indium(III) ions have shown to have a toxic effect on the kidneys when given by injection, however, when taken orally, indium compounds do not have the chronic toxicity of salts of heavy metals, due to poor absorption in basic conditions.


Indium should be stored in closed containers. As it tends to wet glass, it's best to keep it in plastic containers.


Due to its high price, it's best to try to recycle indium, rather than just throw it away.


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