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Chemical element, symbol In and atomic number 49 / From Wikipedia, the free encyclopedia

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Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts per million of the Earth's crust. Indium has a melting point higher than sodium and gallium, but lower than lithium and tin. Chemically, indium is similar to gallium and thallium, and it is largely intermediate between the two in terms of its properties.[8] 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.

Quick facts: Indium, Pronunciation, Appearance, Standard a...
Indium, 49In
Pronunciation/ˈɪndiəm/ (IN-dee-əm)
Appearancesilvery lustrous gray
Standard atomic weight Ar°(In)
  • 114.818±0.001
  • 114.82±0.01 (abridged)[1]
Indium in the periodic table


Atomic number (Z)49
Groupgroup 13 (boron group)
Periodperiod 5
Block  p-block
Electron configuration[Kr] 4d10 5s2 5p1
Electrons per shell2, 8, 18, 18, 3
Physical properties
Phase at STPsolid
Melting point429.7485 K (156.5985 °C, 313.8773 °F)
Boiling point2345 K (2072 °C, 3762 °F)
Density (near r.t.)7.31 g/cm3
when liquid (at m.p.)7.02 g/cm3
Triple point429.7445 K, ~1 kPa[2]
Heat of fusion3.281 kJ/mol
Heat of vaporization231.8 kJ/mol
Molar heat capacity26.74 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1196 1325 1485 1690 1962 2340
Atomic properties
Oxidation states−5, −2, −1, 0,[3] +1, +2, +3[4] (an amphoteric oxide)
ElectronegativityPauling scale: 1.78
Ionization energies
  • 1st: 558.3 kJ/mol
  • 2nd: 1820.7 kJ/mol
  • 3rd: 2704 kJ/mol
Atomic radiusempirical: 167 pm
Covalent radius142±5 pm
Van der Waals radius193 pm
Color lines in a spectral range
Spectral lines of indium
Other properties
Natural occurrenceprimordial
Crystal structure body-centered tetragonal
Body-centered-tetragonal crystal structure for indium
Speed of sound thin rod1215 m/s (at 20 °C)
Thermal expansion32.1 µm/(m⋅K) (at 25 °C)
Thermal conductivity81.8 W/(m⋅K)
Electrical resistivity83.7 nΩ⋅m (at 20 °C)
Magnetic orderingdiamagnetic[5]
Molar magnetic susceptibility−64.0×10−6 cm3/mol (298 K)[6]
Young's modulus11 GPa
Mohs hardness1.2
Brinell hardness8.8–10.0 MPa
CAS Number7440-74-6
DiscoveryFerdinand Reich and Hieronymous Theodor Richter (1863)
First isolationHieronymous Theodor Richter (1864)
Isotopes of indium
Main isotopes[7] Decay
abun­dance half-life (t1/2) mode pro­duct
111In synth 2.8 d ε 111Cd
113In 4.28% stable
115In 95.7% 4.41×1014 y β 115Sn
Symbol_category_class.svg Category: Indium
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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 glass. Indium is considered a technology-critical element.

Indium has no biological role. Its compounds are toxic when injected into the bloodstream. Most occupational exposure is through ingestion, from which indium compounds are not absorbed well, and inhalation, from which they are moderately absorbed.

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