Indium is a chemical element ; it has symbol In and atomic number 49. It is a silvery-white post-transition metal and one of the softest elements. Chemically, indium is similar to gallium and thallium , and its properties are largely intermediate between the two.[10] It was discovered in 1863 by Ferdinand Reich and Hieronymous Theodor Richter by spectroscopic methods and named for the indigo blue line in its spectrum.[11]
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Indium, 49 In Pronunciation (IN -dee-əm ) Appearance silvery lustrous gray
Atomic number (Z ) 49 Group group 13 (boron group) Period period 5 Block p-block Electron configuration [ Kr ] 4d10 5s2 5p1 Electrons per shell 2, 8, 18, 18, 3 Phase at STP solid Melting point 429.7485 K (156.5985 °C, 313.8773 °F) Boiling point 2345 K (2072 °C, 3762 °F) Density (at 20° C) 7.290 g/cm3 [3] when liquid (at m.p. ) 7.02 g/cm3 Triple point 429.7445 K, ~1 kPa[4] Heat of fusion 3.281 kJ/mol Heat of vaporization 231.8 kJ/mol Molar heat capacity 26.74 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
Oxidation states −5, −2, −1, 0,[5] +1, +2, +3 [6] (an amphoteric oxide) Electronegativity Pauling scale: 1.78 Ionization 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 Spectral lines of indiumNatural occurrence primordial Crystal structure body-centered tetragonal (tI2 )Lattice constants a = 325.16 pmc = 494.71 pm (at 20 °C)[3] Thermal expansion 32.2× 10−6 /K (at 20 °C)[lower-alpha 1] Thermal conductivity 81.8 W/(m⋅K) Electrical resistivity 83.7 nΩ⋅m (at 20 °C) Magnetic ordering diamagnetic [7] Molar magnetic susceptibility −64.0× 10−6 cm3 /mol (298 K)[8] Young's modulus 11 GPa Speed of sound thin rod 1215 m/s (at 20 °C) Mohs hardness 1.2 Brinell hardness 8.8–10.0 MPa CAS Number 7440-74-6 Discovery Ferdinand Reich and Hieronymous Theodor Richter (1863)First isolation Hieronymous Theodor Richter (1864)
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Indium is a technology-critical element used primarily in the production of flat-panel displays as indium tin oxide (ITO) , a transparent and conductive coating applied to glass.[12] [13] [14] Indium is also used in the semiconductor industry ,[15] in low-melting-point metal alloys such as solders and soft-metal high-vacuum seals. It is produced exclusively as a by-product during the processing of the ores of other metals, chiefly from sphalerite and other zinc sulfide ores .[16]
Indium has no biological role and its compounds are toxic when inhaled or injected into the bloodstream, although they are poorly absorbed following ingestion.[17] [18]