Elemental aristocracy

Each row of the periodic table ends at the end. A little over a hundred years ago, their existence was not even supposed. Then they amazed the world with their chemical properties, or rather their absence. Even later they turned out to be a logical consequence of the laws of nature. noble gases.

Over time, they "went into action", and in the second half of the last century they began to be associated with less noble elements. Let's start the story of elementary high society like this:

A long time ago…

… There was a lord.

Lord Henry Cavendish (1731-1810) in an old sketch.

Henry Cavendish he belonged to the highest British aristocracy, but he was interested in learning the secrets of nature. In 1766, he discovered hydrogen, and nineteen years later he conducted an experiment in which he was able to find another element. He wanted to find out whether the air contains other components besides the already known oxygen and nitrogen. He filled a bent glass tube with air, immersed its ends in mercury vessels and passed electric discharges between them. The sparks caused the nitrogen to combine with oxygen, and the resulting acidic compounds were absorbed by the alkali solution. In the absence of oxygen, Cavendish fed it into the tube and continued the experiment until all nitrogen was removed. The experiment lasted several weeks, during which the volume of gas in the pipe was constantly decreasing. Once the nitrogen was exhausted, Cavendish removed the oxygen and found that the bubble still existed, which he estimated to be ¹/₁₂₀ initial air volume. The Lord did not ask about the nature of the residues, considering the effect to be a mistake of experience. Today we know that he was very close to opening argon, but it took more than a century to complete the experiment.

solar mystery

Solar eclipses have always attracted the attention of both ordinary people and scientists. On August 18, 1868, astronomers observing this phenomenon first used a spectroscope (designed less than ten years ago) to study solar prominences, clearly visible with a darkened disk. French Pierre Janssen in this way he proved that the solar corona consists mainly of hydrogen and other elements of the earth. But the next day, while observing the Sun again, he noticed a previously undescribed spectral line located near the characteristic yellow line of sodium. Janssen was unable to attribute it to any element known at the time. The same observation was made by an English astronomer Norman Locker. Scientists have put forward various hypotheses about the mysterious component of our star. Lockyer named him high energy laser, on behalf of the Greek god of the sun - Helios. However, most scientists believed that the yellow line they saw was part of the hydrogen spectrum at the star's extremely high temperatures. In 1881, an Italian physicist and meteorologist Luigi Palmieri studied the volcanic gases of Vesuvius using a spectroscope. In their spectrum, he found a yellow band attributed to helium. However, Palmieri described the results of his experiments vaguely, and other scientists did not confirm them. We now know that helium is found in volcanic gases, and Italy may indeed have been the first to observe the terrestrial helium spectrum.

Illustration from 1901 showing the apparatus for the Cavendish experiment

Opening in the third decimal place

At the beginning of the last decade of the XNUMXth century, the English physicist Lord Rayleigh (John William Strutt) decided to accurately determine the densities of various gases, which also made it possible to accurately determine the atomic masses of their elements. Rayleigh was a diligent experimenter, so he obtained gases from a wide variety of sources in order to detect impurities that would falsify the results. He managed to reduce the error of determination to hundredths of a percent, which at that time was very small. The analyzed gases showed compliance with the determined density within the measurement error. This did not surprise anyone, since the composition of chemical compounds does not depend on their origin. The exception was nitrogen - only it had a different density depending on the method of production. Nitrogen atmospheric (obtained from air after the separation of oxygen, water vapor and carbon dioxide) has always been heavier than chemical (obtained by decomposition of its compounds). The difference, oddly enough, was constant and amounted to about 0,1%. Rayleigh, unable to explain this phenomenon, turned to other scientists.

Help offered by a chemist William Ramsay. Both scientists concluded that the only explanation was the presence of an admixture of a heavier gas in the nitrogen obtained from the air. When they came across the description of the Cavendish experiment, they felt they were on the right track. They repeated the experiment, this time using modern equipment, and soon they had a sample of an unknown gas in their possession. Spectroscopic analysis has shown that it exists separately from known substances, and other studies have shown that it exists as separate atoms. So far, such gases have not been known (we have O₂, N₂, H₂), so that also meant opening a new element. Rayleigh and Ramsay tried to make him argon (Greek = lazy) to react with other substances, but to no avail. To determine the temperature of its condensation, they turned to the only person in the world at that time who had the appropriate apparatus. It was Karol Olszewski, professor of chemistry at the Jagiellonian University. Olshevsky liquefied and solidified argon, and also determined its other physical parameters.

The report of Rayleigh and Ramsay in August 1894 caused a great resonance. Scientists could not believe that generations of researchers had neglected the 1% component of air, which is present on Earth in an amount much greater than, for example, silver. Tests by others have confirmed the existence of argon. The discovery was rightfully considered a great achievement and a triumph of careful experiment (it was said that the new element was hidden in the third decimal place). However, no one expected that there would be ...

… A whole family of gases.

Helium group (atomic number at the top, atomic mass at the bottom).

Even before the atmosphere had been thoroughly analyzed, a year later, Ramsay became interested in a geology journal article that reported the release of gas from uranium ores when exposed to acid. Ramsay tried again, examined the resulting gas with a spectroscope and saw unfamiliar spectral lines. Consultation with William Crooks, a specialist in spectroscopy, led to the conclusion that it has long been sought on Earth high energy laser. Now we know that this is one of the decay products of uranium and thorium, contained in the ores of natural radioactive elements. Ramsay again asked Olszewski to liquefy the new gas. However, this time the equipment was not capable of achieving sufficiently low temperatures, and liquid helium was not obtained until 1908.

Helium also turned out to be a monatomic gas and inactive, like argon. The properties of both elements did not fit into any family of the periodic table and it was decided to create a separate group for them. [helowce_uklad] Ramsay came to the conclusion that there are gaps in it, and together with his colleague Morrisem Traversem started further research. By distilling liquid air, chemists discovered three more gases in 1898: neon (gr. = new), krypton (gr. = skryty) i xenon (Greek = foreign). All of them, together with helium, are present in the air in minimal quantities, much less than argon. The chemical passivity of the new elements prompted researchers to give them a common name. noble gases. 

After unsuccessful attempts to separate from the air, another helium was discovered as a product of radioactive transformations. In 1900 Frederic Dorn Oraz André-Louis Debirne they noticed the release of gas (emanation, as they said then) from radium, which they called radon. It was soon noticed that the emanations also emit thorium and actinium (thoron and actinon). Ramsay and Frederick Soddy proved that they are one element and are the next noble gas they named niton (Latin = to glow because the gas samples glowed in the dark). In 1923, nithon finally became radon, named after the longest-lived isotope.

The last of the helium installations that complete the real periodic table was obtained in 2006 at the Russian nuclear laboratory in Dubna. The name, approved only ten years later, Oganesson, in honor of the Russian nuclear physicist Yuri Oganesyan. The only thing known about the new element is that it is the heaviest known so far and that only a few nuclei have been obtained that have lived for less than a millisecond.

Chemical misalliances

Belief in the chemical passivity of helium collapsed in 1962 when Neil Bartlett he obtained a compound of the formula Xe [PtF₆]. The chemistry of xenon compounds today is quite extensive: fluorides, oxides and even acid salts of this element are known. In addition, they are permanent compounds under normal conditions. Krypton is lighter than xenon, forms several fluorides, as does the heavier radon (the latter's radioactivity makes research much more difficult). On the other hand, the three lightest - helium, neon and argon - do not have permanent compounds.

Chemical compounds of noble gases with less noble partners can be compared to old misalliances. Today, this concept is no longer valid, and one should not be surprised that ...

Helicopters, from left to right: Lord Rayleigh (John William Strutt, 1842–1919), Sir William Ramsay (1852–1916) and Morris Travers (1872–1961); portrait from the collection of University College London.

… aristocrats work.

Helium is obtained by separating liquefied air in nitrogen and oxygen plants. On the other hand, the source of helium is mainly natural gas, in which it is up to a few percent of the volume (in Europe, the largest helium production plant operates in Overcame, in Greater Poland Voivodeship). Their first occupation was to shine in luminous tubes. Nowadays, neon advertising is still pleasing to the eye, but helium materials are also the basis of some types of lasers, such as the argon laser that we will meet at the dentist or beautician.

Artist's rendering of the Xenon Ion Probe Dawn near the asteroid Ceres.

The chemical passivity of helium installations is used to create an atmosphere that protects against oxidation, for example, when welding metals or hermetic food packaging. Helium-filled lamps operate at a higher temperature (that is, they shine brighter) and use electricity more efficiently. Usually argon is used mixed with nitrogen, but krypton and xenon give even better results. The latest use of xenon is as a propulsion material in ion rocket propulsion, which is more efficient than chemical propellant propulsion. The lightest helium is filled with weather balloons and balloons for children. In a mixture with oxygen, helium is used by divers to work at great depths, which helps to avoid decompression sickness. The most important application of helium is to achieve the low temperatures required for superconductors to function.

Oxygen-helium mixture ensures safe diving.