home Biology Why did the universe lose lithium? Helium was forced to create a stable chemical compound Lithium and helium are related

Why did the universe lose lithium? Helium was forced to create a stable chemical compound Lithium and helium are related

Three-dimensional structure of the Na2He compound

An international team of scientists from the Moscow Institute of Physics and Technology, Skoltech, Nanjing University and Stony Brook University, led by Artem Oganov, predicted and was able to obtain in the laboratory a stable compound of sodium and helium - Na 2 He. Similar compounds can occur in the bowels of the Earth and other planets, under conditions of very high pressure and temperature. Research published in the journal Nature Chemistry, a press release from the University of Utah also reports briefly on the article. It should be noted that the preliminary version of the work was posted by the authors in the form of a preprint in 2013.

Helium, like neon, is the most chemically inert element in the periodic table and hardly reacts due to its filled outer electron shell, high ionization potential, and zero electron affinity. For a long time, scientists have been trying to find its stable compounds, for example with fluorine (HHeF and (HeO)(CsF)), chlorine (HeCl) or lithium (LiHe), but such substances exist for a limited time. Stable helium compounds exist (these are NeHe 2 and [email protected] 2 O), however, helium there has practically no effect on the electronic structure and is associated with other atoms by van der Waals forces. However, the situation may change if you try to work with high pressures- under such conditions, the noble gases become more active and form compounds, such as oxides with magnesium (Mg-NG, where NG is Xe, Kr or Ar). Therefore, it was decided to search for such compounds with helium.

The researchers conducted a large-scale search for possible stable compounds of helium with various elements(H, O, F, Na, K, Mg, Li, Rb, Cs, etc.) using the USPEX (Universal Structure Predictor: Evolutionary Xtallography) code developed by Oganov and colleagues in 2004. It turned out that only sodium forms a stable compound with He at pressures available for laboratory experiments. Then it was decided to look for a stable compound of the Na-He system with a minimum enthalpy of formation (i.e., the most stable ones) at different pressures. Calculations show that this will be a Na 2 He compound. The formation reaction of this substance is possible at pressures above 160 GPa, while it will be exothermic, i.e. with heat release. At pressures below 50 GPa, the connection will be unstable.

Thermodynamic characteristics of the Na-He system at different pressures

To test the theoretical calculations, it was decided to try to obtain the predicted compound using diamond anvils heated by laser radiation. Thin plates of sodium were loaded into them, and the rest of the space was filled with gaseous helium. During the experiments, scientists took Raman spectra, in addition, the state of the system was monitored visually and using the synchrotron diffraction method. x-ray radiation. The obtained data were then compared with those predicted on the basis of calculations.

Crystal structure of Na2He at 300 GPa (a,b) and distribution of electron density in it (c) a new relative of graphene, two forms of alumina that exist at high pressures, as well as for the first time "gluing" of layers in a superconductor, which, as it turned out, is accompanied by loss of its superconducting properties.

Alexander Voytyuk

Lithium

Helium

Helium occupies the second position in the periodic table after hydrogen. The atomic mass of helium is 4.0026. It is an inert gas without color. Its density is 0.178 grams per liter. Helium is more difficult to liquefy than all known gases only at a temperature of minus 268.93 degrees Celsius and practically does not solidify. Cooled to minus 270.98 degrees Celsius, helium acquires superfluidity. Helium is formed most often as a result of the decay of large atoms. On Earth, it is distributed in small quantities, but on the Sun, where there is an intense decay of atoms, there is a lot of helium. All these data are, as it were, passport data and are well known.

Let's deal with the topologies of helium, and first we will determine its dimensions. Given that atomic mass helium is four times more than hydrogen, and a hydrogen atom is 1840 times heavier than an electron, we get the mass of a helium atom equal to 7360 electrons; hence the total number of ethereal globules in a helium atom is approximately 22,000; the length of the cord of the atom and the diameter of the original torus are respectively equal to 7360 and 2300 ethereal balls. In order to visualize the ratio of the thickness of the cord of the original torus of the helium atom and its diameter, let us draw on a sheet of paper with a pen a circle with a diameter of 370 millimeters, and let the trace from the pen have a width of one third of a millimeter; the resulting circle will give us the indicated representation. One electron (built-in ethereal balls) will occupy only 0.15 millimeters on the drawn circle.

The twisting of the original torus into the finished form of the helium atom occurs as follows. First, the circle is flattened into an oval, then into the shape of a dumbbell, then into a figure eight, and then the loops of the figure eight unfold so that an overlap occurs. By the way, the overlap of larger atoms is not formed, and this is explained by the fact that the length of the cord at the helium atom is not yet large, and when the midpoints of the cord tend to get closer, the edges (loops) are forced to unfold. Further, the edges will bend and begin to converge.

Up to this point, the topology of the helium atom, as we see, is similar to the topology of the atom of the hydrogen isotope - tritium, but if tritium did not have enough strength to close the edges (there was not enough length of its cord), then the helium loops move one on top of the other and thus close . In order to verify the reliability of the connection of the loops, it is enough to follow the location of their suction sides: for the inner loop it will be outside, and for the outer loop it will be from the inside.

It is very convenient to represent the topology of atoms in the form of wire models; to do this, it is enough to use a moderately elastic, but sufficiently plastic wire. The hydrogen atom will be depicted as an ordinary ring. Let's increase the length of a piece of wire by four times (so many times the helium atom is heavier than the hydrogen atom), roll it into a ring, solder the ends and demonstrate the process of twisting the helium atom. When twisting, we must constantly remember that the bending radii should not be less than the radius of the ring, which is a hydrogen atom; it is, as it were, a condition set by the elasticity of the cord - torus shells. (In nature, we recall, the minimum radius was equal to 285 ethereal balls.) The accepted minimum bending radius determines the topology of all atoms; and one more thing: the consequence of the same bending radii will be the same sizes of suction loops (a kind of standardization of them), and therefore they form a stable valency, expressed in the ability to connect different atoms to each other. If the hinges had different sizes, their connection would be problematic.

Bringing the process of twisting the wire model of the helium atom to the end, we find that the overlapped loops are not pushed one on top of the other until they stop. More precisely, they would prefer to twist even further, but the elasticity of the cord does not allow it, that is, the condition of the minimum radius. And with every attempt of the loops to move towards even further, the elasticity of the cord will throw them back; rebounding, they will again rush forward, and again the elasticity will throw them back; in this case, the helium atom will then shrink, then bloom, that is, a pulsation occurs. The pulsation, in turn, will create a standing thermal field around the atom and make it fluffy; so we came to the conclusion that helium is a gas.

Based on topology, other physical and chemical characteristics helium. Its inertness, for example, is indicated by the fact that its atoms have neither open suction loops nor suction channels: it is not able to combine with other atoms at all, therefore it is always atomic and practically does not harden. Helium has no color because its atoms do not have straight “sounding” sections of cords; and superfluidity arises from any lack of viscosity (sticking together of atoms), rounded shape and small size of the atom.

Like hydrogen, helium atoms do not have the same size: some of them are larger, others are smaller, and in general they occupy almost the entire weight space from hydrogen (tritium) to lithium following helium; the less durable isotopes of helium, of course, have already decayed long ago, but it is possible to count more than one hundred that exist at the present time.

In the periodic table, helium is better placed not at the end of the first period - in the same row with hydrogen, but at the beginning of the second period before lithium, because its atom, like the atoms of this entire period, is a single structure (single glomerulus), while how an atom of the next inert gas, neon, already looks like a paired structure, similar in this feature to the atoms of the third period.

Lithium occupies the third number in the periodic table; its atomic mass is 6.94; it belongs to the alkali metals. Lithium is the lightest of all metals: its density is 0.53 grams per cubic centimeter. It is silvery white in color with a bright metallic sheen. Lithium is soft and easily cut with a knife. In air, it quickly dims, combining with oxygen. The melting point of lithium is 180.5 degrees Celsius. Lithium isotopes with atomic weights 6 and 7 are known. The first isotope is used to produce the heavy isotope of hydrogen, tritium; another isotope of lithium is used as a heat transfer fluid in boilers nuclear reactors. These are the general physical and chemical data of lithium.

Let's start the topology of lithium atoms again with an understanding of the dimensions of the original torus. Now we know that every chemical element, including lithium, has a large number of isotopes, measured in hundreds and thousands; therefore, the sizes of atoms will be indicated from ... to .... But what do these limits mean? Can they be determined exactly? Or are they approximate? And what is the ratio of isotopes? Let's say right away: there are no unambiguous answers to the questions posed; each time it is necessary to intrude into a specific topology of atoms. Let's look at these issues using the example of lithium.

As we have noticed, the transition from protium to helium, from the point of view of topology, occurs systematically: with an increase in the size of the initial torus, the final configuration of atoms gradually changes. But physical and especially Chemical properties atoms in the transition from protium to helium change more than significantly, rather radically: from the universal attraction of protium to the complete inertness of helium. Where, on what isotope did this happen?

Such jumps in properties are associated with size jumps of isotopes. A large hydrogen atom (tritium), which takes on the shape of a helium atom, turns out to be radioactive, that is, fragile. This is due to the fact that its curved edges of the loops do not reach each other, and one can imagine how they flutter, rushing towards. They resemble the hands of two people in divergent boats, powerlessly trying to reach out and grapple. External etheric pressure will press on the consoles of fluttering loops of atoms so strongly that it will not lead to good; having received even a slight additional squeezing from the side, the consoles will break off - they will not withstand the sharp bend of the cord, and the atom will collapse; that's how it happens. Therefore, we can say that dips are observed among isotopes at the boundaries of existing physicochemical transitions: there are simply no isotopes there.

A similar gap exists between helium and lithium: if an atom is no longer helium, but not yet lithium, then it is fragile, and it has long been absent from terrestrial conditions. Therefore, the lithium isotope with an atomic weight of six, that is, with a torus cord length of 11 ethereal balls, is very rare and, as said, is used to obtain tritium: it is easy to break it, shorten it and get an isotope of hydrogen as a result.

Thus, we, it seems, have decided on the smallest size of a lithium atom: these are 11 bound electrons. As for its upper limit, there is some snag here: the fact is that, according to topology, the lithium atom does not differ much from the atom of the next beryllium atom (we will soon see this), and there are no isotopes of either element no failure. Therefore, for the time being, we will not indicate the upper limit of the size of the lithium atom.

Let us follow the formation of the lithium atom. The initial circle of a newly formed microvortex with the dimensions indicated above will tend to turn into an oval; only in lithium, the oval is very long: approximately 8 times longer than the diameter of the end rounding (future loop); it is a very elongated oval. The beginning of the clotting of the lithium atom is similar to the same beginning for large hydrogen atoms and for helium, but then a deviation occurs: the figure-eight with an overlap, that is, with a turn of the loops, does not occur; further convergence of the long sides (cords) of the oval until they are in full contact is accompanied by a simultaneous bending of the ends towards each other.

Why is an eight with an overlap not formed? First of all, because the oval is very long, and even its full deflection in the dumbbell until the cords touch in the middle does not cause them to bend strongly; therefore, the potential for reversal of the extreme loops is very weak. And secondly, the beginning of the bending of the ends of the oval counteracts the turn to some extent. In other words: the active moment of forces tending to turn the end loops is very small, and the moment of resistance to the turn is large.

For clarity, we will use rubber rings, for example, those used in machine seals. If you pinch a ring of small diameter, then it will definitely curl into a figure eight with an overlap; and if you choose a ring of large diameter, then its pinching until the cords are in full contact does not cause a turn of the end loops. By the way: these rubber rings are also very convenient for modeling the topology of atoms; if, of course, there is a wide range of them.

The bending of the ends of the oval is caused, as we already know, by the disturbance of the ether between them: having slightly moved away from the ideally straight position, they will already be forced to approach until they completely touch. So in different sides the ends cannot be bent. But with the direction of the bend, they have a choice: either so that the suction sides of the end loops are outside, or inside. The first variant is more probable, because the moment from the forces of repulsion of the rotating shells of the cord from the adjacent ether at the outer points of the loops will be greater than at the inner ones.

The approaching sides of the oval will very soon come into contact, the bow of the cords will spread from the center to the ends and stop only when loops with the minimum allowable bending radii are finally formed at the ends. Simultaneously occurring bends and mutual convergence of these loops lead to a collision of their vertices, after which their suction sides come into play: the loops, sucking, dive deep; and the process of formation of the configuration of the lithium atom is completed by the fact that the displaced loops abut their vertices against the paired cords exactly in the center of the structure. Remotely, this configuration of the atom resembles a heart or, more precisely, an apple.

The first conclusion suggests itself: the lithium atom begins when the tops of the paired primary loops that have dived into the structure reach the cords of the middle of the atom. And before that there was still not lithium, but some other element, which is now no longer in nature; its atom was extremely unstable, pulsated very strongly, was therefore fluffy and belonged to gases. But the atom of the very initial lithium isotope (we defined it as consisting of 11,000 bound electrons) also turns out to be not very strong: the bending radii of its loops are limiting, that is, the elastic cords are bent to the limit, and with any external impact they are ready to burst. For larger atoms, this weak point is eliminated.

Representing the image of a lithium atom based on the results of the topology, one can evaluate what happened. The two primary loops closed and neutralized, and the secondary loops on either side of the primary loops were also neutralized. The paired cords created a groove, and this groove runs along the entire contour of the atom - it is, as it were, closed in a ring - and its suction side turned out to be outside. From this it follows that lithium atoms can combine with each other and with other atoms only with the help of their suction grooves; a lithium atom cannot form a loop molecular compound.

Strongly convex suction troughs of lithium atoms can be connected to each other only in short sections (theoretically, at points), and therefore the spatial structure of lithium atoms connected to each other turns out to be very loose and sparse; hence the low density of lithium: it is almost two times lighter than water.

Lithium - metal; its metallic properties result from the peculiarities of the shapes of its atoms. It can be said in another way: special properties lithium, which are due to the special forms of its atoms and which make it physically and chemically different from other substances, are called metallic; Let's look at some of them:

electrical conductivity: it arises from the fact that the atoms are ring-shaped from paired cords, creating suction troughs, open outward, embracing the atoms along the contour and closing on themselves; electrons stuck to these grooves can freely move along them (we recall once again that difficulties arise when electrons are separated from atoms); and since the atoms are connected to each other by the same grooves, then the electrons have the ability to jump from atom to atom, that is, to move around the body;

thermal conductivity: elastically curved cords of an atom form an extremely rigid elastic structure, which practically does not absorb low-frequency large-amplitude (thermal) shocks of neighboring atoms, but transmits them further; and if there were no possible disturbances in their contacts (dislocations) in the thickness of the atoms, then the thermal wave would propagate with great speed;
brilliance: high-frequency low-amplitude impacts of light waves of the ether are easily reflected from the tensely bent cords of atoms and go away, obeying the laws of wave reflection; the lithium atom does not have straight sections of cords, therefore it does not have its own “sound”, that is, it does not have its own color - lithium is therefore silvery white with a strong shine on the sections;
plasticity: rounded lithium atoms can be connected to each other in any way; they can, without breaking, roll over each other; and this is expressed in the fact that a body made of lithium can change its shape without losing its integrity, that is, be plastic (soft); as a result, lithium is cut without much difficulty with a knife.

Using the example of the noted physical features of lithium, one can clarify the very concept of metal: metal is a substance composed of atoms with sharply curved cords forming contoured suction troughs open to the outside; atoms of pronounced (alkaline) metals do not have open suction loops and straight or smoothly curved cord sections. Therefore, lithium under normal conditions cannot combine with hydrogen, since the hydrogen atom is a loop. Their connection can only be hypothetical: in deep cold, when hydrogen solidifies, its molecules can combine with lithium atoms; but everything shows that their alloy would be as soft as lithium itself.

At the same time, we clarify the concept of plasticity: the plasticity of metals is determined by the fact that their rounded atoms can roll over each other, changing the relative position, but without losing contacts with each other.

Beryllium occupies the fourth position in the periodic table. Its atomic mass is 9.012. It is a light gray metal with a density of 1.848 grams per cubic centimeter and a melting point of 1284 degrees Celsius; it is hard and at the same time fragile. Structural materials based on beryllium are both light, strong, and resistant to high temperatures. Beryllium alloys, being 1.5 times lighter than aluminum, are nevertheless stronger than many special steels. They retain their strength up to a temperature of 700 ... 800 degrees Celsius. Beryllium is resistant to radiation.

In terms of its physical properties, as can be seen, beryllium is very different from lithium, but in terms of the topology of atoms, they are almost indistinguishable; the only difference is that the beryllium atom is, as it were, “sewn with a margin”: if the lithium atom resembles a tight suit of a schoolboy on an adult, then the beryllium atom, on the contrary, is a spacious suit of an adult on a child’s figure. The excess length of the cord of the beryllium atom, with the same configuration of it with lithium, forms a more gentle outline with bending radii exceeding the minimum critical ones. Such a “reserve” of curvature for beryllium atoms allows them to be deformed up to reaching the limit of filament bending.

The topological similarity of lithium and beryllium atoms indicates that there is no clear boundary between them; and it is impossible to say which is the largest atom of lithium and which is the smallest atom of beryllium. Focusing only on the tabular atomic weight (and it averages all values), we can assume that the cord of a medium-sized beryllium atom consists of approximately 16,500 bound electrons. Upper limit The size of beryllium isotope atoms rests on the minimum size of an atom of the next element - boron, the configuration of which differs sharply.

The margin of curvature of the cords of beryllium atoms primarily affects their connection to each other at the moment of solidification of the metal: they are adjacent to each other not by short (dotted) sections, like in lithium, but by long boundaries; the contours of the atoms, as it were, adjust to each other, deforming and adhering to each other in the maximum possible way; so these connections are very strong. Beryllium atoms also show their strengthening ability in compounds with atoms of other metals, that is, in alloys in which beryllium is used as an additive to heavy metals: filling voids and sticking with their flexible grooves to the atoms of the base metal, beryllium atoms hold them together like glue, making the alloy is very durable. Hence it follows that the strength of metals is determined by the lengths of the stuck together sections of the suction troughs of atoms: The longer these sections, the stronger the metal. The destruction of metals always occurs along the surface with the shortest sticky sections.

The margin for bending radii of the cords of beryllium atoms allows them to be deformed without changing the connections between them; as a result, the whole body is deformed; this is an elastic deformation. It is elastic because in any initial state the atoms have the least stressed forms, and when deformed they are forced to endure some “inconvenience”; and as soon as the deforming force disappears, the atoms return to their original, less stressed states. Hence, the elasticity of a metal is determined by the excess length of the cords of its atoms, which allows them to be deformed without changing the areas of interconnection.

The elasticity of beryllium is related to its heat resistance; it is expressed in the fact that the thermal motions of atoms can occur within the limits of elastic deformations that do not cause a change in the compounds of atoms among themselves; so in general the heat resistance of the metal is determined, as well as elasticity, excess lengths of cords of its atoms. The decrease in the strength of the metal at high heating is explained by the fact that the thermal movements of its atoms reduce the areas of their connections to each other; and when these areas completely disappear, the metal melts.

The elasticity of beryllium is accompanied by its fragility. Fragility can be considered in the general case as the opposite of plasticity: if plasticity is expressed in the ability of atoms to change their mutual positions while maintaining the connecting areas, then fragility is expressed, first of all, in the fact that atoms do not have such a possibility. Any mutual displacement of the atoms of a brittle material can only occur when their bonds are completely broken; these atoms have no other variants of compounds. In elastic materials (in metals), brittleness is also characterized by the fact that it is, as it were, jumping: a crack that has arisen as a result of excessive stresses spreads with lightning speed over the entire cross section of the body. For comparison: a brick under hammer blows can crumble (this is also fragility), but not split. The “jumping” brittleness of beryllium is explained by the fact that its atoms are not interconnected in the best way, and they are all stressed; and as soon as one bond is broken, the boundary atoms rapidly begin to “straighten up” to the detriment of connections with their neighbors; the ties of the latter will also begin to break down; and this process will take a chain character. Hence, the fragility of elastic metals depends on the degree of deformation of the interconnected atoms and on the inability to change the bonds between them.

The radiation resistance of beryllium is explained by the same reserve in the size of its atoms: the cord of the beryllium atom has the ability to spring under a hard radiation impact, not reaching its critical curvature, and thereby remain intact.

And the light gray color of beryllium and the absence of a bright metallic luster, such as, for example, lithium, can be explained in the same way: light waves of the ether, falling on non-rigid cords of surface atoms of beryllium, are absorbed by them, and only a part of the waves is reflected and creates a scattered light.

The density of beryllium is almost four times greater than that of lithium only because the density of the cords of its atoms is higher: they are connected to each other not at points, but in long sections. At the same time, in its continuous mass, beryllium is a rather loose substance: it is only twice as dense as water.

Russian and foreign chemists declare the possibility of the existence of two stable compounds of the most "xenophobic" element - helium, and experimentally confirmed the existence of one of them - sodium helide, according to an article published in the journal Nature Chemistry.

"This study demonstrates how completely unexpected phenomena can be detected using the most modern theoretical and experimental methods. Our work once again illustrates how little we currently know about the impact of extreme conditions on chemistry, and the role of such phenomena on processes inside planets has yet to be explained,” says Artem Oganov, professor at Skoltech and the Moscow Institute of Physics and Technology in Dolgoprudny.

Secrets of noble gases

The primary matter of the Universe, which arose several hundred million years after big bang, consisted of only three elements - hydrogen, helium and trace amounts of lithium. Helium is still the third most abundant element in the universe today, but it is extremely rare on Earth, and helium reserves on the planet are constantly decreasing due to the fact that it escapes into space.

A distinctive feature of helium and other elements of the eighth group of the periodic table, which scientists call "noble gases", is that they are extremely reluctant - in the case of xenon and other heavy elements - or in principle, like neon, are not able to enter into chemical reactions. There are only a few dozen compounds of xenon and krypton with fluorine, oxygen and other strong oxidizing agents, zero compounds of neon and one helium compound, discovered experimentally in 1925.

This compound, the union of a proton and helium, is not a real chemical compound in the strict sense of the word - helium in this case does not participate in the formation of chemical bonds, although it affects the behavior of hydrogen atoms deprived of an electron. As chemists previously assumed, "molecules" of this substance should have been found in the interstellar medium, but over the past 90 years, astronomers have not discovered them. Possible cause This is that this ion is extremely unstable and is destroyed upon contact with almost any other molecule.

Artem Oganov and his team wondered if helium compounds could exist under exotic conditions that terrestrial chemists rarely think about - at ultra-high pressures and temperatures. Oganov and his colleagues have been studying such "exotic" chemistry for a long time and even developed a special algorithm for searching for substances that exist under such conditions. With his help, they discovered that in the bowels of the gas giants and some other planets, exotic orthocarbonic acid, "impossible" versions of the usual table salt, and a number of other compounds that "violate" the laws of classical chemistry.

Using the same system, USPEX, Russian and foreign scientists found that at ultra-high pressures exceeding atmospheric pressure by 150 thousand and a million times, there are two stable helium compounds at once - sodium oxygelide and sodium helide. The first compound is made up of two sodium atoms and one helium atom, while the second is made up of oxygen, helium and two sodium atoms.

Atom on a diamond anvil

Both pressures can be easily obtained using modern diamond anvils, which Oganov's colleagues did under the guidance of another Russian, Alexander Goncharov from the Geophysical Laboratory in Washington. As his experiments showed, sodium gelide forms at a pressure of about 1.1 million atmospheres and remains stable up to at least 10 million atmospheres.

Interestingly, sodium helide is similar in structure and properties to fluorine salts, helium's "neighbor" on the periodic table. Each helium atom in this "salt" is surrounded by eight sodium atoms, similar to the structure of calcium fluoride or any other salt of hydrofluoric acid. The electrons in Na2He are "attracted" to the atoms so strongly that this compound, unlike sodium, is an insulator. Scientists call such structures ionic crystals, since electrons take the role and place of negatively charged ions in them.

"The compound we have discovered is very unusual: although helium atoms are not directly involved in chemical bond, their presence fundamentally changes the chemical interactions between sodium atoms, contributing to the strong localization of valence electrons, which makes the resulting material an insulator,” explains Xiao Dong from Nankang University in Tianjin (China).

Another compound, Na2HeO, turned out to be stable in the pressure range from 0.15 to 1.1 million atmospheres. The substance is also an ionic crystal and has a structure similar to Na2He, only the role of negatively charged ions in them is played not by electrons, but by oxygen atoms.

Interestingly, all other alkali metals, which have a higher reactivity, are much less likely to form compounds with helium at pressures exceeding atmospheric pressure by no more than 10 million times.

Oganov and his colleagues attribute this to the fact that the orbits along which electrons move in potassium, rubidium, and cesium atoms change noticeably with increasing pressure, which does not happen with sodium, for reasons that are not yet clear. Scientists believe that sodium gelide and other similar substances can be found in the cores of some planets, white dwarfs and other stars.

You may have heard the phrase "you are made of stardust" - and it's true. Many of the particles that make up your body, and the world around you, were formed inside stars billions of years ago. But there are some materials that were formed at the very beginning, after the birth of the Universe.

Some astronomers believe they appeared just a few minutes after the Big Bang. The most common elements in the universe are hydrogen and helium, and very few chemical like lithium.

Astronomers can determine with little accuracy how much lithium was in the early Universe. To do this, you need to explore the oldest stars. But the results obtained do not match - in old stars it turned out to be 3 times less lithium than expected to be found! The reason for this mystery is still unknown.

Let's take a closer look...

Strictly speaking, at the current level of our observations, there should be no error: there is very little lithium. The situation clearly hints at some new physics, a process unknown to us that took place immediately after the Big Bang.

The most recent study on this topic has touched upon the regions least changed since the Big Bang - the atmospheres of old stars located on the periphery of the Milky Way. Since they are isolated from the core, where lithium can be produced, the likelihood of late contamination affecting the results should be extremely small. Their atmospheres contain only about a third of the level predicted by the simulations for lithium-7. Causes? One explanation offered is that he drowned. Lithium from the atmosphere of stars simply began to sink into the matter of the stars, gradually reaching their depths. Therefore, it is not visible in their atmospheres.

Christopher Hawk of the University of Notre Dame (Indiana, USA) and colleagues undertook to verify the results based on data from the Small Magellanic Cloud, a satellite galaxy of the Milky Way. And in order to get rid of the data from the effect of “plunging lithium” and other influences of local stellar processes, the researchers analyzed the contents of interstellar gas in this dwarf galaxy, suggesting that he should be proud of his lithium: he simply has nothing to drown in here.

Using observations from the European Southern Observatory's Very Large Telescope, astronomers found just as much lithium as the Big Bang model predicted, as reported in the journal Nature. But this, alas, did not help much in resolving the issue. The fact is that lithium is constantly formed in the Universe in the course of natural processes, and supernova explosions evenly distribute it throughout the Metagalaxy, like all other elements produced in the depths. New results, according to Christopher Hawke, only exacerbated the lithium mystery: “We can only talk about a solution to this problem if there has been no change in the amount of lithium available since the Big Bang.” And that is only on the scale of the Small Magellanic Cloud!

Most importantly, it is very difficult to imagine that in 12–13 billion years of thermonuclear fusion, which created those very heavy elements who make possible life for some reason, lithium was not produced on Earth. At least our current understanding of thermonuclear nucleosynthesis does not allow us to put forward such a hypothesis.

Even worse, new work by Miguel Pato of the Technical University of Munich (Germany) and Fabio Iocco of the University of Stockholm (Sweden) has shown that not only supermassive black holes in the cores of galaxies, but also the most common (and more numerous) black holes of stellar origin should generate lithium in their accretion disks, and quite intensively.

Now it turns out that almost every microquasar (simply the BH system - an accretion disk) must create lithium. But theoretically, there should be much more of them than SMBH, notes Miguel Pato.

In short, there is no clarity on this issue yet. Christopher Hawke, for example, suggests that immediately after the Big Bang, some exotic reactions from a physical point of view could take place in the Universe, in which dark matter particles participated, and they suppressed the formation of lithium. This could explain why there is more lithium in the Small Magellanic Cloud than in our Galaxy: dwarf galaxies, which include the MMO, should have been less active in attracting dark matter in the early Universe. This means that these hypothetical reactions had less effect on the concentration of lithium in them. Mr. Hawk intends to test this idea with the help of a more in-depth study of the Small Magellanic Cloud ...

Until now, we could only look for lithium in the nearest stars of our Galaxy. And so a group of astronomers was able to determine the level of lithium content in a star cluster outside our Galaxy.

The star cluster Messier 54 has a secret - it does not belong to the Milky Way, and is part of a satellite galaxy - a dwarf elliptical galaxy in Sagittarius. This location of the cluster allowed scientists to check whether the abundance of lithium in stars outside the Milky Way is also low.

In the vicinity of the Milky Way, there are more than 150 globular star clusters, which consist of hundreds of thousands of ancient stars. One such cluster, along with others in the constellation Sagittarius, was discovered in the late 18th century by the French comet hunter Charles Messier, and bears his name Messier 54.

For more than two centuries, scientists have mistakenly believed that M54 is the same cluster as all the others in the Milky Way, but in 1994 it was discovered that this star cluster belongs to another galaxy - the dwarf elliptical galaxy in Sagittarius. The object was also found to be 90,000 light-years from Earth, more than three times the distance between the Sun and the center of the galaxy.

AT this moment Astronomers are monitoring M54 with the VLT Survey as they try to solve one of the most puzzling questions in modern astronomy, the presence of lithium in stars.

In this picture you can see not only the cluster itself, but also a very dense foreground, consisting of the stars of the Milky Way. Photo by ESO.

Previously, astronomers were only able to determine the abundance of lithium in the stars of the Milky Way. However, a research team led by Alessio Mucciarelli of the University of Bologna has now used the VLT Survey to measure the abundance of lithium in the extragalactic star cluster M54. The study showed that the amount of lithium in the old stars M54 does not differ from the stars of the Milky Way. Therefore, wherever lithium disappears, Milky Way it's completely irrelevant here.

metallic lithium

Lithium is the lightest metal, 5 times lighter than aluminum. Lithium got its name because it was found in "stones" (Greek λίθος - stone). The name was suggested by Berzelius. It is one of three elements (besides hydrogen and helium) that formed during the era of primordial nucleosynthesis after the Big Bang, even before the birth of stars. Since then, its concentration in the universe has remained virtually unchanged.

Lithium can rightly be called the most important element of modern civilization and technology development. In the past and the century before last, the indicators of the production of the most important acids and metals, water and energy carriers were the criteria for the development of the industrial and economic power of states. In the 21st century, lithium has firmly and permanently entered the list of such indicators. Today, lithium is of exceptional economic and strategic importance in advanced industrial countries.

By studying the new star Nova Delphini 2013 (V339 Del), astronomers were able to detect the chemical precursor of lithium, thus making the first direct observations of the processes of formation of the third element in the periodic table - which had previously been assumed only theoretically.

“Until now, scientists have not had direct evidence of lithium production in new stars, but after our study, we can say that such processes are taking place,” said the main author of the new scientific work Akito Taitsu of the National Observatory of Japan.

Explosions of new stars occur when, in a close binary star system, matter flows from one of its constituent stars to the surface of a companion star - a white dwarf. An uncontrolled thermonuclear reaction causes a sharp spike in the luminosity of a star, which, in turn, leads to the formation of elements heavier than hydrogen and helium, which are present in significant quantities inside most of the stars of the universe.

One of chemical elements, formed as a result of such an explosion, is the widespread lithium isotope Li-7. While most of the heavy chemical elements are formed in the cores of stars and in supernova explosions, Li-7 is too fragile an element to withstand the high temperatures maintained in most stellar cores.

Some of the lithium present in the universe was formed as a result of the Big Bang. In addition, some amounts of lithium could be formed as a result of the interaction of cosmic rays with stars and interstellar matter. However, these processes do not explain too much large quantities lithium present in the universe today.

In the 1950s scientists have suggested that lithium in the universe can be formed from the beryllium isotope Be-7, which forms near the surface of stars and can be transferred to space, where the impact is reduced high temperatures on the material, and the newly formed lithium remains in a stable state. However, until now, observations from the Earth of lithium formed near the surface of a star have been a rather difficult task.

Taitsu and his team used the Subaru Telescope in Hawaii for their observations. During the observation period, the team clearly recorded how the nuclide Be-7, which has a half-life of 53 days, turned into Li-7.

The lithium helium molecule LiHe is one of the most fragile molecules known. Its size is more than ten times the size of water molecules.

As is known, neutral atoms and molecules can form more or less stable bonds with each other in three ways. First, with the help of covalent bonds, when two atoms share one or more common electron pairs. Covalent bonds are the strongest of the three. The characteristic energy of their rupture is usually equal to several electron volts.

Significantly weaker covalent hydrogen bonds. This is the attraction that occurs between a bound hydrogen atom and an electronegative atom of another molecule (usually such an atom is oxygen or nitrogen, less often fluorine). Despite the fact that the energy of hydrogen bonds is hundreds of times less than that of covalent bonds, it is they that largely determine physical properties water, and also play a crucial role in the organic world.

Finally, the weakest is the so-called van der Waals interaction. Sometimes it is also called dispersed. It arises as a result of the dipole-dipole interaction of two atoms or molecules. In this case, dipoles can either be inherent in molecules (for example, water has a dipole moment), or be induced as a result of interaction.

The characteristic energy of the van der Waals bond is units of kelvin (the electron volt mentioned above corresponds to about 10,000 kelvin). The weakest of the van der Waals is the coupling between two induced dipoles. If there are two non-polar atoms, then as a result of thermal motion, each of them has a certain randomly oscillating dipole moment (the electron shell, as it were, trembles slightly relative to the nucleus). These moments, interacting with each other, as a result predominantly have such orientations that two atoms begin to attract.

The most inert of all atoms is helium. He does not enter covalent bonds not with any other atom. At the same time, the value of its polarizability is very small, that is, it is difficult for it to form dispersed bonds. There is, however, one important circumstance. The electrons in a helium atom are so strongly bound by the nucleus that it can be brought very close to other atoms without fear of repulsive forces - up to a distance of the order of the radius of this atom. The dispersed forces grow very quickly with decreasing distance between atoms - inversely proportional to the sixth power of the distance!

Hence the idea was born: if you bring two helium atoms close to each other, then a fragile van der Waals bond will nevertheless arise between them. This, indeed, was realized in the mid-1990s, although it required considerable effort. The energy of such a bond is only 1 mK, and the He₂ molecule has been detected in small amounts in supercooled helium jets.

At the same time, the properties of the He₂ molecule are in many ways unique and unusual. So, for example, its size is ... about 5 nm! For comparison, the size of a water molecule is about 0.1 nm. At the same time, the minimum potential energy of the helium molecule falls on a much shorter distance - about 0.2 nm - however, most of the time - about 80% - helium atoms in the molecule spend in the tunneling mode, that is, in the region where they are located within the framework of classical mechanics could not.

This is what a helium molecule looks like.
The average distance between atoms far exceeds their size.
© Institut für Kernphysik, J. W. Goethe Universität

The next largest atom after helium is lithium, so after obtaining the helium molecule, it became natural to study the possibility of fixing the connection between helium and lithium. In 2013, scientists finally managed to do just that. The lithium-helium LiHe molecule has a higher binding energy than helium-helium - 34 ± 36 mK, and the distance between atoms, on the contrary, is smaller - about 2.9 nm. However, even in this molecule, atoms most of the time are in the classically forbidden states under the energy barrier. Interestingly, the potential well for the LiHe molecule is so small that it can exist in only one vibrational energy state, which is actually a doublet split due to the spin of the ⁷Li atom. Its rotation constant is so large (about 40 mK) that the excitation of the rotational spectrum leads to the destruction of the molecule.

Potentials of the molecules under discussion (solid curves) and the squared modulus of the wave functions of atoms in them (dashed curves). Points are also marked PM - potential minimum, OTP - external turning point for the lowest energy level, MIS - weighted average distance between atoms.
© Brett Esry/Kansas State University

So far, the results obtained are interesting only from a fundamental point of view. However, they are already of interest to related fields of science. Thus, helium clusters of many particles can become a tool for studying the effects of delay in the Casimir vacuum. The study of the helium-helium interaction is also important for quantum chemistry, which could test its models on this system. And, of course, there is no doubt that scientists will come up with other interesting and important applications for such extravagant objects as He₂ and LiHe molecules.