The helium is a chemical element whose symbol is He. It is the first noble gas in the periodic table, and it is usually located at the extreme right of it. Under normal conditions it is an inert gas, since none of its few compounds is stable; It also expands very quickly and is the substance with the lowest boiling point of all.
At a popular level, it is a well-known gas, since in countless events or children's parties it is common to witness a balloon rise until it is lost in the sky. However, what is really and forever lost to the corners of the solar system, and beyond, are the helium atoms that are released once the balloon explodes or deflates..
In fact, there are those who, and with good reason, consider that helium balloons represent an inappropriate practice for this gas. Luckily, it has more important and interesting uses, thanks to its physical and chemical properties that separate it from other chemical elements..
For example, liquid helium is so cold that it can freeze anything, like a metallic alloy, turning it into a superconducting material. Likewise, it is a liquid that manifests superfluidity, capable of climbing up the walls of a glass container..
Its name is due to the fact that it was identified for the first time on the Sun and not on Earth. It is the second most abundant element in the entire Universe and, although its concentration is negligible in the earth's crust, it can be obtained from the reserves of natural gas and radioactive minerals of uranium and thorium..
Here helium demonstrates another curious fact: it is a gas that is much more abundant in the subsoil than in the atmosphere, where it ends up escaping from the Earth and its gravitational field.
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Helium was not discovered on Earth but on the Sun. In fact, its name comes from the Greek word 'helios' which means sun. The existence of the element by itself contrasted the periodic table of Dmitri Mendeleev, since there was no place in it for a new gas; that is, by then absolutely nothing was suspected about noble gases.
The name 'helium', written as 'helium' in English, ended with the suffix -ium referring to it as a metal; precisely because the existence of a gas other than oxygen, hydrogen, fluorine, chlorine and nitrogen could not be admitted.
This name was designated by the English astronomer Norman Lockyer, who studied from England what was observed by the French astronomer Jules Janssen in India, during a solar eclipse in 1868.
It was a yellow spectral line of a hitherto unknown element. Lockyer claimed that this was due to the presence of a new chemical element found in the Sun.
In 1895, almost twenty years later, the Scottish chemist Sir William Ramsay recognized the same spectrum from a remnant gas when he studied a radioactive mineral: cleveite. So there was helium here on Earth too.
Helium is a colorless, odorless gas that has no taste and is also inert. However, when an electric shock is applied, and depending on the voltage difference, it begins to glow as a grayish-purple haze (image above), then glow with an orange glow. Therefore, the helium lights are orange.
two
4.002 g / mol
-272.2 ºC
-268.92 ºC
-0.1786 g / L, under normal conditions, that is, in the gas phase.
-0.145 g / mL, at melting point, liquid helium.
-0.125 g / mL, just as the helium starts to boil.
-0.187 g / mL, at 0 K and 25 atm, that is, solid helium at those specific pressure and temperature conditions.
2.177 K and 5.043 kPa (0.04935 atm)
5.1953 K and 0.22746 MPa (2.2448 atm)
0.0138 kJ / mol
0.0829 kJ / mol
20.78 J / (mol K)
0.9869 atm at 4.21 K. This value gives you an idea of how fleeting helium can be and how easily it can escape at room temperature (close to 298 K).
-First: 2372.3 kJ / mol (He+ gaseous)
-Second: 5250.5 kJ / mol (Hetwo+ gaseous)
The ionization energies for helium are especially high because the gaseous atom must lose an electron, which experiences a strong effective nuclear charge. It can also be understood by considering the small size of the atom and how “close” the two electrons are to the nucleus (with its two protons and two neutrons).
0.97 mL is dissolved in water for every 100 mL of water at 0 ºC, which means that it is poorly soluble.
Helium is the second least reactive chemical element in nature. Under normal conditions it is correct to say that it is an inert gas; Never (it seems) can a helium compound be manipulated in a room or laboratory without enormous pressures acting on it; or maybe dramatically high or low temperatures.
An example we see in the compound NatwoHe, which is stable only under a pressure of 300 GPa, reproduced in a diamond anvil cell.
While the chemical bonds in NatwoThey are "strange" because they have their electrons well located in the crystals, they are far from being simple Van der Walls interactions and, therefore, they do not simply consist of helium atoms trapped by molecular aggregates. This is where the dilemma arises between which helium compounds are real and which are not.
For example, nitrogen molecules at high pressures can trap a helium atom to form a kind of clathrate, He (Ntwo)eleven.
Likewise, there are the endohedral complexes of fullerene cations, C60+n and C70+n, in whose cavities they can accommodate helium atoms; and the molecular cation HeH+ (He-H+), found in very distant nebulae.
Who out of curiosity tries to calculate the oxidation number for helium in any of its compounds will find that this is equal to 0. In NatwoHe, for example, could be thought that its formula corresponds to hypothetical Na ionstwo+I havetwo-; but such would be to assume that it has a pure ionic character, when in reality its bonds are far from being so.
Furthermore, helium does not gain electrons because it cannot accommodate them in the 2s orbital, energetically unavailable; and it is not possible to lose them either, due to the small size of its atom and the great effective nuclear charge of its nucleus. That is why helium always participates (in theory) as an atom He0 in its derived compounds.
Helium, like all gases observed on a macroscale, occupies the volume of the containers that stores it, thus having an indefinite shape. However, when the temperature drops and begins to cool below -269 ºC, the gas condenses into a colorless liquid; helium I, the first of the two liquid phases for this element.
The reason why helium condenses at such a low temperature is due to the low scattering forces that hold its atoms together; whatever the phase considered. This can be explained from its electronic configuration:
1stwo
In which two electrons occupy the 1s atomic orbital. The helium atom can be visualized as an almost perfect sphere, whose homogeneous electronic periphery is little prone to polarization by the effective nuclear charge of the two protons in the nucleus..
Thus, spontaneous and induced dipole moments are rare and very weak; so the temperature must approach absolute zero so that the He atoms approach slowly enough and achieve that their dispersive forces define a liquid; or even better, a helium crystal.
In the gas phase the space that separates the He atoms is such that it can be assumed that they are always separated from each other. So much so that in a small-volume vial, the helium appears colorless until it is subjected to an electrical discharge, which ionizes its atoms in a greyish and dimly-lit haze..
However, in the liquid phase He atoms, even with their weak interactions, can no longer be "ignored". Now the dispersion force allows them to momentarily join together to form dimers: He-He or Hetwo. Hence, helium I can be thought of as vast clusters of Hetwo in equilibrium with its atoms in the vapor phase.
This is why helium I is so difficult to differentiate from its vapors. If this liquid is spilled out of its airtight container, it escapes as a whitish flare..
When the temperature drops even more, touching 2,178 K (-270,972 ºC), a phase transition occurs: helium I is transformed into helium II.
From this point, the already fascinating helium liquid becomes a superfluid or quantum fluid; that is, their macroscopic properties are manifested as if the dimers Hetwo they were individual atoms (and perhaps they are). It lacks complete viscosity, as there is no surface that can stop an atom during its sliding or "climbing".
That is why helium II can climb the walls of a glass container overcoming the force of gravity; no matter how high they are, as long as the surface remains at the same temperature and therefore does not volatilize.
Due to this, liquid helium cannot be stored in glass containers, since it would escape at the slightest crack or gap; very similar to how it would happen with a gas. Instead, stainless steel is used to design such vessels (Dewars tanks).
Even if the temperature dropped to 0 K (absolute zero), the scattering force between the He atoms would not be strong enough to order them into a crystalline structure. For solidification to occur, the pressure must rise to approximately 25 atm; and then compact hexagonal helium crystals (hcp) appear.
Geophysical studies show that this hcp structure remains unchanged no matter how much pressure increases (up to the order of gigapascals, GPa). However, there is a narrow region in their pressure-temperature diagram where these hcp crystals undergo a transition to a body-centered cubic phase (bcc)..
Helium is the second most abundant element in the entire Universe, second only to hydrogen. Stars constantly produce immeasurable amounts of helium atoms through the fusion of two hydrogen nuclei during the nucleosynthesis process..
Likewise, any radioactive process that emits α particles is a source of production of helium atoms if they interact with the electrons in the environment; for example, with those of a rocky body in deposits of radioactive minerals of uranium and thorium. These two elements undergo radioactive decay, starting with uranium:
Therefore, in the rocks where these radioactive minerals are concentrated, the helium atoms will be trapped, which will be released once they are digested in acidic media..
Among some of these minerals are cleveite, carnotite, and uraninite, all composed of uranium oxides (UOtwo or U3OR8) and thorium, heavy metal and rare earth impurities. Helium, irrigated through underground channels, can end up accumulating in natural gas reservoirs, mineral springs or in meteoric irons.
It is estimated that a mass of helium equivalent to 3000 tons is produced annually in the lithosphere, from the radioactive decay of uranium and thorium..
Helium is not very soluble in water, so sooner rather than later it ends up ascending from the depths (wherever its origin is), until it crosses the layers of the atmosphere and finally reaches outer space. Its atoms are so small and light that the gravitational field of the Earth cannot retain them in the atmosphere..
Due to the above, the concentration of helium both in the air (5.2 ppm) and in the seas (4 ppt) is very low..
If we wanted to extract it from either of these two media, the “best” option would be air, which would first have to be subjected to liquefaction to condense all its component gases, while the helium remains in a gaseous state..
However, it is not practical to obtain helium from the air, but from rocks enriched with radioactive minerals; or better yet, from natural gas reserves, where helium can represent up to 7% of its total mass.
Instead of liquefying the air, it is easier and more profitable to use natural gas, whose helium composition is undoubtedly much greater. Thus, the raw material par excellence (commercial) for obtaining helium is natural gas, which can also be subjected to fractional distillation.
The final product of the distillation is finished by purifying with activated carbon, through which a very pure helium passes through. And finally, helium is separated from neon by a cryogenic process where liquid helium is used..
Helium occurs predominantly in nature as the isotope 4He, whose bare nucleus is the famous α particle. This atom of 4He has two neutrons and two protons. In less abundance is the isotope 3He, which has only one neutron. The first is heavier (has a higher atomic mass) than the second.
Thus, the isotope pair 3I have and 4He are those that define the measurable properties and what we understand of helium as a chemical element. Since the 3He is lighter, it is assumed that its atoms have higher kinetic energy and that, therefore, they need an even lower temperature to cohesion in a superfluid.
The 3He is considered a very rare species here on Earth; however, in lunar soils it is more abundant (2000 times more, approximately). That is why the Moon has been the subject of projects and stories as a possible source of 3He, which could be used as nuclear fuel for the spacecraft of the future.
Among other isotopes of helium, the following can be mentioned, with their respective half-lives: 5I have (t1/2= 7.610−22 s), 6I have (t1/2= 0.8 s) and 8I have (t1/2= 0.119 s).
Helium is an inert gas and therefore does not participate in any of the reactions that occur within our bodies..
Its atoms practically come in and out exhaled without their interactions with biomolecules producing an ulterior effect; except for the sound emitted from the vocal cords, which become higher-pitched and have higher frequency.
People who inhale helium from a balloon (in moderation) speak in a high-pitched voice, similar to that of a squirrel (or duck).
The problem is that if such a person inhales an inappropriate amount of helium, he runs the risk of suffocation, since its atoms displace the oxygen molecules; and therefore, you will not be able to breathe until you exhale all that helium, which in turn due to its pressure can tear the lung tissue or cause barotrauma.
Cases have been reported of people who have died from inhaling helium because of what has just been explained.
On the other hand, although it does not represent a fire risk given its lack of reactivity towards oxygen (or another substance), if it is stored under high pressure and escapes, its leak can be physically dangerous..
The physical and chemical properties of helium not only make it a special gas, but also a very useful substance for applications requiring extremely low temperatures. In this section some of these applications or uses will be addressed..
In some systems it is necessary to increase the pressure (pressurize), and for this a gas must be injected or supplied that does not interact with any of its components; e.g. with reagents or surfaces sensitive to undesirable reactions.
Thus, the pressure can be increased with volumes of helium, whose chemical inertness makes it ideal for this purpose. The inert atmosphere that it facilitates exceeds in certain cases that of nitrogen.
For the reverse process, that is, the purge, helium is also used due to its ability to entrain all oxygen, water vapors or any other gas, whose presence you want to remove. In this way the pressure of the system is reduced once the helium has been emptied..
Helium can leak through the slightest crack, so it is also used to detect leaks in pipes, high-vacuum containers or cryogenic tanks.
Sometimes detection can be done visually or by touch; however, mostly a detector is what “gives” the signal of where and how much helium is escaping from the system under inspection..
Helium atoms, as mentioned for purge systems, can carry with them, depending on their pressure, heavier molecules. For example, this principle is used daily in gas chromatography analysis, since it can drag the atomized sample along the column, where it interacts with the stationary phase..
Due to its low density compared to air and, again, its lack of reactivity with oxygen, it has been used to inflate balloons at children's parties (mixed with oxygen so that no one suffocates from breathing it), and airships (top image) , without representing a risk of fire.
When divers descend to greater depths, they find it difficult to breathe due to the great pressure exerted by the water. That is why helium is added to their oxygen tanks to decrease the density of the gas that divers breathe and exhale, and thus, it can be exhaled with less work..
In the welding process, the electric arc provides enough heat for the two metals to come together. If done under a helium atmosphere, the incandescent metal will not react with the oxygen in the air to become its respective oxide; therefore helium prevents this from happening.
Liquid helium is so cold that it can freeze metals into superconductors. Thanks to this, it has been possible to manufacture very powerful magnets, which, cooled with liquid helium, have been used in image scanners or nuclear magnetic resonance spectrometers..
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