The Indian It is a metal that belongs to group 13 of the periodic table and has the chemical symbol In. Its atomic number is 49, 49In, and occurs in nature as two isotopes: 113In and 115In, the latter being the most abundant. On Earth, indium atoms are found as impurities in zinc and lead ores..
It is a particular metal, since it is the softest that can be touched without many health risks; unlike lithium and rubidium, which would burn the skin terribly when reacting with their moisture. A piece of indium can be cut with a knife and fractured with the force of the fingers, emitting a distinctive crunch.
Whoever hears this metal name will surely come to mind India, but its name derives from the indigo color, which is observed when the flame test is carried out. In this sense it is quite similar to potassium, burning its metal or its compounds with a very characteristic flame, through which indium was detected for the first time in sphalerite minerals..
Indium shares many chemical qualities with aluminum and gallium, occurring in most of its compounds with an oxidation number of +3 (In3+). It combines excellently with gallium, forming alloys with low melting points, one of which is galinstan..
Indium applications are based on coating materials with their alloys, making them electrically conductive and flexible. The Indian covers some glasses to give them greater brilliance, replacing silver. In the world of technology, the Indian is found in touchscreens and LCD.
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In 1863, the German chemist Ferdinand Reich was looking for traces of the element thallium, by means of the green line of its emission spectrum, in zinc minerals; specifically samples of sphalerite (ZnS) around Saxony. After roasting the minerals, removing their sulfur content, digesting them in hydrochloric acid, and distilling off the zinc chloride, he obtained a straw-colored precipitate..
Before the finding, Reich decided to carry out a spectroscopic analysis; but because he did not have good eyes to observe colors, he turned to his colleague Hieronymus Theodor Richter for help in this task. Richter was the one who observed a bluish spectral line, which did not coincide with the spectrum of any other element..
The two German chemists were facing a new element, which received the name of Indian because of the indigo color of the flame when its compounds were burned; and in turn, the name of this color derives from the Latin word indicum, what does India mean.
A year later, in 1864, excited and after a prolonged series of precipitations and purifications, they isolated a sample of metallic indium by electrolysis of its dissolved salts in water..
Indium atoms, In, coalesce using their valence electrons to establish a metallic bond. Thus, they end up being arranged in a crystal with a distorted tetragonal structure centered in the body. The interactions between the neighboring In-In atoms in the crystal are relatively weak, which explains why indium has a low melting point (156 ºC)..
On the other hand, the forces that unite two or more indium crystals are not strong either, otherwise they would not move on top of each other, giving the metal its characteristic softness..
It is a remarkably soft silvery metal. It can be torn with fingernail pressure, cut with a knife, or scratched in shiny strokes on a sheet of paper. It is even possible to chew it and deform it with your teeth, as long as it is flattened. Likewise, it is very ductile and malleable, having plastic properties.
When the Indian is heated with a blowtorch, it gives off an indigo-colored flame, even brighter and more colorful than that of potassium..
114.81 g / mol
156.60 ºC
2072 ºC.
Like gallium, indium has a wide temperature range between its melting point and boiling point. This reflects the fact that the In-In interactions in the liquid are stronger than those that predominate in the glass; and that therefore it is easier to obtain a drop of indium than its vapors.
At room temperature: 7.31 g / cm3
Right at melting point: 7.02 g / cm3
1.78 on the Pauling scale
First: 558.3 kJ / mol
Second: 1820.7 kJ / mol
Third: 2704 kJ / mol
81.8 W / (m K)
83.7 nΩm
1,2. It is only slightly harder than talcum powder (do not confuse toughness with toughness).
Indium dissolves in acids to form salts, but does not dissolve in alkaline solutions, not even with hot potassium hydroxide. Reacts in direct contact with sulfur, oxygen and halogens.
Indium is relatively amphoteric, but it behaves more like a base than an acid, its aqueous solutions being slightly basic. The In (OH)3 redissolves with the addition of more alkalis, giving rise to the complex indiates, In (OH)4-, just as it happens with aluminates.
The electron configuration of the indium is as follows:
[Kr] 4d10 5stwo 5 p1
Of those thirteen electrons, the last three of the 5s and 5p orbitals are the valence electrons. With these three electrons, the indium atoms establish their metallic bond, as do aluminum and gallium, and form covalent bonds with other atoms..
The above said serves to understand at once that the indium is capable of losing its three valence electrons, or gaining five to become isoelectronic to the noble gas xenon..
If in a compound we assume that it has lost its three electrons, it will remain as the trivalent cation In3+ (in analogy to Al3+ and Ga3+) and therefore its oxidation number will be +3. Most indium compounds are In (III).
Among other oxidation numbers found for indium we have: -5 (In5-), -2 (Intwo-), -1 (In-), +1 (In+) and +2 (Intwo+).
Some examples of In (I) compounds are: InF, InCl, InBr, InI and IntwoO. All of them are relatively rare compounds, while those of In (III) are the predominant ones: In (OH)3, IntwoOR3, InCl3, InF3, etc.
In (I) compounds are powerful reducing agents, in which In+ donates two electrons to other species to become In3+.
Indium occurs in nature as two isotopes: 113In and 115In, whose terrestrial abundances are 4.28% and 95.72%, respectively. Therefore, on Earth we have many more atoms of 115In what of 113In. The 115In has a half-life of 4.41 · 1014 years, so large that it is practically considered stable, despite being a radioisotope.
At present, a total of 37 artificial isotopes of indium have been created, all radioactive and highly unstable. Of all of them, the most stable is the 111In, which has a half-life of 2.8 days.
The Indian gets along very well with the gallium. Both metals form alloys that melt at low temperatures, looking like silver liquids, with which mercury is supplanted in several of its applications. Likewise, indium also amalgamates easily, having a solubility of 57% in mercury.
Indium alloys are used to design silver mirrors without the need for silver. When poured onto a surface of any material, it acts as an adherent, in such a way that glass, metal, quartz and ceramic plates can join.
Indium also gets along well with germanium, so its compounds are added as dopants to germanium nitride in LEDs, reproducing blue, purple and green lights from these mixtures. It is also part of transistors, thermistors and photovoltaic cells.
The most important of its compounds is indium tin oxide, which is used as a coating on glasses to reflect some wavelengths. This allows it to be used in welding goggles, and skyscraper glass so they don't get hot inside..
Glasses coated with this oxide are good conductors of electricity; like that coming from our fingers. And that is why it is intended for the manufacture of touch screens, an activity even more current today due to the emergence of more and more smartphones..
Indium does not represent any risk to the environment in the first instance, since its ions In3+ they are not disseminated in appreciable quantities. There is no information regarding what would be its impact on soils, affecting plants, and neither on fauna or the seas..
In the body it is not known whether In3+ they have some essential role in metabolism in trace amounts. However, when its compounds are ingested, they are harmful to various organs, which is why they are considered highly toxic substances.
In fact, ITO (Indium Tin Oxide) particles: Indium Tin Oxide), essential for the manufacture of screens for computers and smartphones, can have a negative impact on the health of workers, causing them a disease called Indian lung.
The ingestion of these particles occurs mainly by inhalation and by contact through the skin and eyes..
On the other hand, fine indium metal particles are prone to burning and causing fires if they are near a heat source..
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