Indium: Properties and Occurrences

Indium is a chemical element with symbol In and atomic number 49. It is a soft, ductile, manleable, lustrous metallic metal. It is a post-transition metal that makes up 0.21 parts per million of the Earth’s crust. Indium was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter by spectroscopic methods. They named it for the indigo blue line in its spectrum. Indium was isolated the next year.

Chemical properties

Chemically, indium is similar to gallium and thallium, and it is largely intermediate between the two in terms of its properties.

  • Atomic number: 49
  • Atomic mass: 114.82 g.mol-1
  • Electronegativity according to Pauling: 2
  • Density: 7.31 at 20°C
  • Melting point: 156 °C
  • Boiling point: 2000 °C
  • Vanderwaals radius: 0.162 nm
  • Ionic radius: 0.092 nm (+2)
  • Isotopes: 11

Fig: Indium – a chemical element

Physical properties

Indium is a silvery-white, highly ductile post-transition metal with a bright luster. It is so soft (Mohs hardness 1.2) that like sodium, it can be cut with a knife. It also leaves a visible line on paper. It is a member of group 13 on the periodic table and its properties are mostly intermediate between its vertical neighbor’s gallium and thallium.

  • Colour: Grey
  • Luster: Metallic
  • Hardness: 3
  • Crystal System: Tetragonal
  • Diaphaneity: Opaque

Indium is a minor component in zinc sulfide ores and is produced as a byproduct of zinc refinement. It is most notably used in the semiconductor industry, in low-melting-point metal alloys such as solders, in soft-metal high-vacuum seals, and in the production of transparent conductive coatings of indium tin oxide (ITO) on the glass.


Indium is used in low-melting fusible alloys and as a protective plate for bearings and other metal surfaces. It can be used to form corrosion-resistant mirror surface: when evaporated and allowed to deposit on glass it produces a mirror as good a quality as that of silver

The following are the application areas of indium:

  • Rectifiers
  • Solar cells
  • Thermistors
  • Semiconductors
  • Photoconductors
  • To dope germanium to make transistors
  • To make mirrors and low melting alloys.


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