Artificial elements - part 1
Almost two years ago, the International Union of Pure and Applied Chemistry, an organization of chemists from around the world, announced the names of four new elements. Thus, the chapter in the history of chemistry has come to an end - the seventh period of the periodic table has finally been completed, and since then there are officially 118 chemical elements.
However, the IUPAC decision (
Lifespan
To estimate the lifetime of radioactive elements, physicists use the concept of half-life. This is the time until half of the original amount of the element remains. However, after a second of the same amount of time, the entire element will not disappear, but only half of the half or a quarter of the original amount will remain. Etc. Theoretically, even after an infinitely long period of time, some fraction of the original amount will remain, but in practice it is assumed that after ten periods there is practically no radioactive material left.
Electric wires, ring and aluminum can certainly testify to the existence of copper, gold and aluminum. As you know from school, air contains nitrogen and oxygen. Reactive elements such as sodium and chlorine form table salt. We also have these elements, and our imagination suggests that somewhere on the shelves of chemical laboratories there are samples of them. If the concept of a laboratory is extended to places where highly radioactive elements are also stored, then it turns out that the last of the existing ones is Einstein, with serial number 99. Colloquially, existence should be understood as the presence of an element or its compound in tangible quantities. To do this, it is necessary to have at least a millionth of a gram, otherwise even the smallest crystals of a chemical compound will not form (in the case of element 100 - firm - information on the receipt of the required quantity is not fully confirmed).
The Curies demonstrate the radiation of radium (painting by André Castaigne, 1903).
She had to face this problem at the beginning of the last century. The radiation of radium and polonium was not enough for the chemists of that time to recognize the existence of these elements - only the isolation of a fraction of a gram of their compounds convinced the doubters. But let's not criticize the traditionalists. This approach is very practical: there is little that can be done in an ordinary laboratory with such a small amount of a substance that it cannot even be seen.
The reason for the "non-existence" is, of course, the lifetime of some elements - too short to survive until now after the formation of the Earth from cosmic dust. Supernova explosions produce even the heaviest elements, which then dissipate within light years of the exploding star. Under favorable conditions, the crumbs merge into larger clusters, and those into planets. However, 4,5 billion years is definitely too long for certain elements to remain on our globe in appreciable quantities (the heavier, the less and the shorter lives). Therefore, in order to subject them to research, it was necessary to create the missing elements of matter. Not to open, because they did not exist, hidden from the "glass and eyes" of scientists, but simply to produce.
Even the heaviest elements are formed in supernova explosions. The Hubble image shows the Crab Nebula in the constellation Taurus, the remnant of the supernova of 1054.
Mama franço's hair and astatue?
Very little. It is estimated that no more than 50 grams of a franc are located in the earth's crust at any one time. Astatine is even less - about a gram! In both cases, the reason is in the very short lifetime of natural isotopes, and in addition, in the inefficient way of formation - they are formed in the side branches of radioactive series with a low probability of their own transformation. Not surprisingly, so far no one has singled out the visible part of these elements, and it does not seem that in the near future.
The division is not as obvious as it might seem at first glance. We're pretty good at classifying in the case of handmade items like bolts or nuts. However, when we enter an area of nature where the boundaries are not sharp, problems arise in the form of objects that can be assigned to different groups.
It's the same with elements. Uranium is the heaviest element, the lifetime of which allowed it to survive to this day (the half-life is comparable to the age of our planet, so we still have about half of the uranium that was part of the young Earth). Elements more massive than it were created by man (more on this later in the series), but some of them were later discovered as by-products of transformations caused by the decay of uranium nuclei.
Fraud from a Czech mine in the Sudetes. Uranium ores are a source of many radioactive elements.
A similar situation arises with unstable elements weighing less than uranium. Some of them have a very short lifespan (for French it's only 20 minutes and for astatu seconds at most, although the artificially obtained isotope of this element has a half-life of eight hours), and their existence in nature is only a consequence of the constant supply of decaying uranium and thorium nuclei (see: Radioactive series). The two elements located in the middle of the periodic table - TechNet i traffic - despite decades of efforts by chemists, they are not found in nature. Only after they were obtained, it became clear that they are the product of a very rare, spontaneous fission of uranium nuclei and were identified in extremely small quantities in the ores of this metal.
Also, some man-made elements are better understood than long-established, ingrained elements. In some cases, the production of artificial substances exceeds the entire world supply of simple substances considered natural (see: How many francs and astatine do we have?)! The reason, of course, is the use: about 20 tons of radioactive plutonium are used annually, while almost no one needs metallic strontium and its production reaches kilograms. Add to this the fact that the earth's surface is contaminated by products of nuclear power plants and nuclear explosions (mostly nuclei are lighter than uranium) and thermonuclear ones (in this case they are also heavier than uranium), and we will have a complete picture of the difficulty of carrying out a seemingly simple fission: natural or artificial element?
Nuclear weapons tests "enriched" the environment with numerous radioactive elements.
The greatest achievement of chemistry in the 150th century was construction (next year, Mendeleev's work "turns" XNUMX years old!). The genius of its creator was revealed, among other things, in the fact of leaving vacancies for yet undiscovered elements and predicting their properties. As the gaps in the table were filled (some predictions failed), the question arose: how many elements actually exist?
Henry Moseley (1887-1915) and X-ray spectrum images of several elements.
The answer was given by a young, under 26 years old English physicist Henry Mosley, in 1913. During an internship in the laboratory of the discoverer of the atomic nucleus, Ernest Rutherfordstudied X-ray emission of excited atoms. He managed to connect the wavelengths of the emitted X-rays with the charge of atomic nuclei, and this one was different for each element, constituting a uniquely defining feature. However, the Great War soon broke out, Moseley was mobilized and fell at Gallipoli two years later. Studies have shown that the heaviest known - uranium - has 92 protons in the nucleus, which means the same number of elements (at least at that time). It also meant that seven elements were missing from the periodic table at positions 43, 61, 72, 75, 85, 87 and 91. Chemists and physicists went on a scientific hunt, the easier it was because they knew where and what to look for - the location of unknown elements in the periodic table made it possible to determine their properties and intended locations.
Row of radioactive uranium and radium (atomic number on the bottom, isotope mass number on the left).
radioactive series - two isotopes of uranium and one of thorium with a long life span decay with the formation of also radioactive nuclei. These in turn undergo further decay, and so on. After a dozen or so changes, permanent isotopes of lead are eventually formed. The sequence of isotopes, one of which arises from the other, is the radioactive series. After receiving Neptune, it turned out that one of its isotopes also started the series. However, the relatively short lifetime of its members meant that this number was obsolete in nature, and the only remnant of it is the presence of the last in the series - bismuth.
In 1923 it was discovered harrow (No. 72), and two years later - Ren (No. 75). The discoverers of the latter faced the same problem as our compatriot a few years earlier. And they, too, had to process a large amount of ore in order to obtain visible samples of the compounds of the new element. They used the Moseley method for identification. They also saw frequencies in the spectrum that pointed to another element from the same group, number 43, but their observations were not confirmed. Technet, because we are talking about him, the first of the elements was obtained artificially (Latin = artificial), in 1937, as a result of the bombardment of molybdenum (No. 42) with nuclei of the hydrogen isotope (No. 1). This element is radioactive, although its long life allows it to be used. Later it turned out that technetium occurs in nature as a result of the spontaneous decay of uranium nuclei.
Radiation source marking. It is better not to approach containers with this sign!
During the research, natural radioactive arrays were discovered protactin (No. 91) i французский (No. 87). However, element 85 was first obtained artificially by bombarding a bismuth target (No. 83) with alpha particles (helium nuclei containing two protons and two neutrons). Due to its very short half-life, the new element was named summer (gr. = fickle). Knowledge of its chemical properties made it possible a few years later to detect astatine in uranium and thorium ores, where it appears as one of their decay products.
The last of the missing trafficwith 61 protons in the nucleus - identified in 1945 during the study of spent uranium fuel residues in the reactor. The name of the element comes from the mythical Prometheus, who, like the Olympic flame in the past, brought a new source of energy to mankind. This element is also present in trace amounts in uranium ores.
