The rhenium It is a metallic element whose chemical symbol is Re, and it is located in group 7 of the periodic table, two places below manganese. It shares with this and technetium the property of exhibiting multiple numbers or oxidation states, from +1 to +7. It also forms an anion called perrhenate, ReO4-, analogous to permanganate, MnO4-.
This metal is one of the rarest and scarces in nature, so its price is high. It is extracted as a by-product of molybdenum and copper mining. One of the most relevant properties of rhenium is its high melting point, barely surpassed by carbon and tungsten, and its high density, being twice that of lead..
His discovery has controversial and unfortunate overtones. The name 'rhenium' derives from the Latin word 'rhenus', which means Rhine, the famous German river near the site where the German chemists who isolated and identified this new element worked..
Rhenium has numerous uses, among which the refinement of the octane number of gasoline stands out, as well as in the manufacture of refractory superalloys, destined for the assembly of turbines and engines of aerospace ships..
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The existence of two heavy elements with chemical characteristics similar to those of manganese had already been predicted since the years 1869, through the periodic table of the Russian chemist Dmitri Mendeleev. However, it was not known by then what their atomic numbers should be; and it was here in 1913 that the prediction of the English physicist Henry Moseley was introduced.
According to Moseley, these two elements belonging to the manganese group must have atomic numbers 43 and 75.
A couple of years earlier, however, the Japanese chemist Masataka Ogawa had discovered the putative element 43 in a sample of the mineral torianite. After announcing his results in 1908, he wanted to baptize this element with the name 'Niponio'. Unfortunately, chemists at the time showed that Ogawa had not discovered element 43.
And so, other years passed when in 1925 three German chemists: Walter Noddack, Ida Noddack, and Otto Berg, found element 75 in mineral samples of columbite, gadolinite, and molybdenite. These gave him the name of rhenium, in honor of the river Rhine of Germany ('Rhenus', in Latin).
Masataka Ogawa's mistake was to have made the wrong identification of the element: he had discovered rhenium, not element 43, today called technetium..
Rhenium is usually marketed as a grayish powder. Its metallic pieces, generally spherical drops, are silver-gray, which are also highly shiny..
186.207 g / mol
75
3186 ºC
5630 ºC
-At room temperature: 21.02 g / cm3
-Right at melting point: 18.9 g / cm3
Rhenium is a metal that is almost twice as dense as lead itself. Thus, a sphere of rhenium weighing 1 gram can be equated to a robust lead crystal of the same mass.
1.9 on the Pauling scale
First: 760 kJ / mol
Second: 1260 kJ / mol
Third: 2510 kJ / mol
25.48 J / (mol K)
48.0 W / (mK)
193 nΩ m
7
Rhenium atoms occur in nature as two isotopes: 185Re, with an abundance of 37.4%; Y 187Re, with an abundance of 62.6%. Rhenium is one of those elements whose most abundant isotope is radioactive; however, the half-life of the 187Re is very large (4.121010 years), so it is practically considered stable.
Rhenium metal is a material resistant to rust. When it does, its rust, RetwoOR7, it volatilizes at high temperatures and burns with a yellowish-green flame. Rhenium pieces resist HNO attack3 concentrated; but when hot, it dissolves to generate rhenic acid and nitrogen dioxide, which turns the solution brown:
Re + 7HNO3 → HReO4 + 7 NOtwo + 3HtwoOR
The chemistry of rhenium is vast, as it is capable of forming compounds with a wide spectrum of oxidation numbers, as well as establishing a quadrupole bond between two rhenium atoms (four Re-Re covalent bonds)..
Rhenium atoms group together in their crystals to form a compact hexagonal structure, hcp, which is characterized by being very dense. This is consistent with the fact that it is a high-density metal. The metallic bond, product of the overlap of their external orbitals, keeps the Re atoms strongly cohesive.
In this metallic bond, Re-Re, the valence electrons participate, which are according to the electronic configuration:
[Xe] 4f14 5 d5 6stwo
In principle, it is the 5d and 6s orbitals that overlap to compact the Re atoms in the hcp structure. Note that its electrons add up to a total of 7, corresponding to the number of its group in the periodic table..
The electronic configuration of rhenium allows us to see at once that its atom is capable of losing up to 7 electrons, to become the hypothetical cation Re7+. When the existence of the Re is assumed7+ in any rhenium compound, for example, in RetwoOR7 (Retwo7+OR7two-), is said to have an oxidation number of +7, Re (VII).
Other positive oxidation numbers for rhenium are: +1 (Re+), +2 (Retwo+), +3 (Re3+), and so on up to +7. Also, rhenium can gain electrons by becoming an anion. In these cases, it is said to have a negative oxidation number: -3 (Re3-), -2 (Retwo-) and -1 (Re-).
Rhenium, along with platinum, is used to create catalysts that increase the octane rating of gasoline, while lowering its lead content. On the other hand, rhenium catalysts are used for multiple hydrogenation reactions, this due to their resistance to being poisoned by nitrogen, phosphorus and sulfur..
Rhenium is a refractory metal due to its high melting point. That is why it is added to nickel alloys to make them refractory and resistant to high pressures and temperatures. These superalloys are mostly used for the design of turbines and engines for aerospace ships..
Rhenium can also form alloys with tungsten, which improves its ductility and therefore facilitates the manufacture of the filaments. These rhenium-tungsten filaments are used as X-ray sources, and for the design of thermocouples capable of measuring temperatures up to 2200 ºC..
Likewise, these rhenium filaments were once used for the flashes of archaic cameras, and now for the lamps of sophisticated equipment; such as the mass spectrophotometer.
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