How many unpaired electrons does indium have

Name, symbol, atomic number Indium, In, 49
Group, period, block13, 5, p
Look silvery glossy gray
Mass fraction of the earth's envelope 1 · 10−5 %
Atomic mass 114,818 u
Atomic radius (calculated) 155 (156) pm
Covalent radius 144 pm
Van der Waals radius 193 pm
Electron configuration [Kr] 4d105s25p1
Electrons per energy level 2, 8, 18, 18, 3
1. Ionization energy 558.3 ​​kJ / mol
2. Ionization energy 1820.7 kJ / mol
3. Ionization energy 2704 kJ / mol
Physical state firmly
Modifications a
Crystal structuretetragonal
density 7.31 g / cm3
Mohs hardness 1,2
Melting point 429,7485[1] K (156.5985 ° C)
boiling point 2345 K (2072 ° C)
Molar volume 15,76 · 10−6 m3/ mol
Heat of evaporation 231,8[2] kJ / mol
Heat of fusion 3.26 kJ / mol
Vapor pressure

1 Pa at 1196[3] K

Speed ​​of sound 1215 m / s at 293.15 K.
Specific heat capacity 233 J / (kg K)
Electric conductivity 12,5 · 106S / m
Thermal conductivity 81.6 W / (m K)
Oxidation states3, 1
Oxides (basicity) (amphoteric)
Normal potential −0.343 V (In3+ + 3e → In)
Electronegativity 1.78 (Pauling scale)
NMR properties
  Spinγ in
rad · T−1· S−1
E. fL. at
W = 4.7 T
in MHz
113In 9/2 5,8845 · 107 0,0151 21,87
115In9/2 5.8972 · 1070,271 38,86
safety instructions
Hazardous substance labeling
R and S phrases R: 11[4]
S: 9-16-29-33[4]
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions.

Indium is a chemical element with the symbol In and the atomic number 49. In the periodic table of the elements it is in the 5th period and is the fourth element of the 3rd main group (after recounting group 13) or boron group. Indium is a rare, silvery white and soft metal. It is considered to be one of the first elements whose natural occurrences will be completely depleted.[5] Indium is not essential for humans, nor are toxic effects known[6]. Most of the metal is processed into indium tin oxide, which is used in flat screens and touch screens.


Indium was discovered in 1863 by the German chemists Ferdinand Reich and Theodor Richter at the Bergakademie Freiberg. They examined a sphalerite sample found in the area for thallium. Instead of the expected thallium lines, they found a previously unknown indigo blue spectral line and thus a previously unknown element in the absorption spectrum. According to this, the new element was later given its name. A short time later, they were initially able to produce indium chloride and oxide, and also the metal by reducing indium oxide with hydrogen. A large amount of indium was first shown at the 1867 World's Fair in Paris.[7]

After its first use in 1933 as an alloy component in dental gold, the extensive use of indium began with the Second World War. The United States used it as a coating in highly stressed aircraft bearings. After the Second World War, indium was mainly used in the electronics industry, as a soldering material and in low-melting alloys. Use in control rods of nuclear reactors also became important with the increasing use of nuclear energy. This led to the first sharp rise in the price of indium by 1980. However, after the Three Miles Island nuclear accident, both demand and price fell significantly.[8]

From 1987 two new indium compounds, the semiconductor indium phosphide and the transparent indium tin oxide, which is conductive and transparent in thin layers, were developed. Indium tin oxide in particular became technically interesting with the development of liquid crystal screens. Due to the high demand, most of the indium has been processed into indium tin oxide since 1992.[8]


Indium is a rare element, its share in the continental crust is only 0.05 ppm[9]. It is thus of a similar frequency as silver and mercury. So far, indium has only been found in a solid state in one single find in eastern Siberia.[10] Only a few indium minerals are known. These are mainly sulphidic minerals such as Indit FeIn2S.4 and Roquésit CuInS2[11]. However, these are rare and do not play a role in the extraction of indium. The largest deposits of indium are in zinc ores, especially sphalerite. Theoretical reserves are estimated at 6000 tons, of which only 2800 tons are economically exploitable[12]. The largest deposits are in Canada and China. Ores containing indium are also found in Australia, Bolivia, Brazil, Japan, Russia, South Africa, the USA and some European countries. In Germany there are sites in the Erzgebirge (Freiberg, Marienberg) and on the Rammelsberg in the Harz Mountains.[7]

Extraction and presentation

Indium is obtained almost exclusively as a by-product in the production of zinc or lead. Economic extraction is possible if indium accumulates at certain points in the production process. These include flue dusts that arise during the roasting of zinc sulfide and residues that are left behind during electrolysis during the wet process of zinc production.[13] These are reacted with sulfuric acid or hydrochloric acid and thus brought into solution. Since the concentration of indium in the acid is too low, it has to be enriched. This is done, for example, by extraction with tributyl phosphate or precipitation as indium phosphate.

The actual indium production takes place electrolytically. A solution of indium (III) chloride in hydrochloric acid is used for this. This is converted into elemental indium with the help of mercury electrodes. During electrolysis, care must be taken that the solution no longer contains thallium, as the standard potentials of the two elements are very similar[13].

By suitable processes such as zone melting processes[14] or repeated electrolysis of indium (I) chloride molten salts[13] the crude product can be further purified and over 99.99% pure indium can be obtained.


The production of indium in 2005 was 500 tons[12]. Due to the low natural reserves and high demand, indium is one of the scarcest raw materials on earth. On the basis of extrapolations with constant consumption and, at the same time, no major new discoveries of deposits are expected before 2015.[5]

country metric tons % of world production
People's Republic of China 300 60
Japan 70 14
Canada 50 10
Belgium 30 6
Russia 15 3
Germany 10 2
France 10 2
Peru 6 1,2
other 10 1,8
total (rounded) 500 100

The indium production in China has only recently increased. In 1994 the amount produced was 10 tons[15]