This stable monoisotopic element belongs to block p, to group 13
and to period 5 and to group IIIA called boron of the periodic table as well as
to the family of poor metals. The atomic radius of indium is around 150 pm (1.50
Å).
The simple indium In body is a shiny gray metal, with a low melting point barely
above 156 ¡ă C, resistant to atmospheric corrosion.
This malleable metal has a chemistry quite similar to aluminum and gallium, but
also to cadmium and thallium. The electronegativity according to Pauling is of
the order of 1.7 (̠8), while those of Ga and Al are around 1.6 and 1.5
respectively.
It is rare. Indium remained a ¡°metal or laboratory element¡± until the beginning
of the interwar period10. In 1924, we discovered that indium can stabilize
non-ferrous metals11. In 1940, indium as a long-lasting protective and
anti-corrosion coating improved ball bearings in military aeronautical
equipment. In the early 1970s, according to chemist Bruce Mahan (en), indium did
not show any significant use. In the early 1980s, the chemical contributors to
the Encyclopedia Universalis admitted that there are few indium compounds
studied and well known (probably for applications). Its recent massive use,
particularly in LCD flat screens, has increased its price from 80 to 800 € / kg
(70 to 1 000 $ / kg at current rates12) between 2001 and 200513,14. The current
shortage makes it a critical mineral raw material.
Indium has 39 known isotopes, with a mass number varying between 97 and 135, and
47 nuclear isomers. Among these isotopes, only one is stable, 113In, making
indium a monoisotopic element. However, natural indium also consists and even
predominantly (~ 95.7%) of a weakly radioactive radioisotope, 115In, with a
half-life of around 441,000 billion years, which means that indium is not a
mononucleidic element. Indium also shares the characteristic with rhenium and
tellurium of having a long-lived natural radioisotope more abundant than its
stable isotope (s). The standard atomic mass attributed to indium is 114.818 (3)
u
magnesium bismuth manganese chromium cobalt titanium
Tungsten vanadium niobium indium molybdenum antimony
rhenium germanium zirconium cadmium hafnium
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