Technetium

TECHNETIUM-I; m.[from Greek. technetos - artificial] Chemical element (Tc), a silver-gray radioactive metal obtained from the waste of the nuclear industry.

◁ Technetium, th, th.

technetium

(lat. Technetium), a chemical element of group VII of the periodic system. Radioactive, the most stable isotopes are 97 Tc and 99 Tc (half-life, respectively, 2.6 10 6 and 2.12 10 5 years). The first artificially obtained element; synthesized by the Italian scientists E. Segre and C. Perriez in 1937 by bombarding molybdenum nuclei with deuterons. Named from the Greek technētós - artificial. Silver gray metal; density 11.487 g / cm 3, t pl 2200°C. It is found in nature in small quantities in uranium ores. Spectrally detected on the Sun and some stars. Obtained from the waste of the nuclear industry. Catalyst component. Isotope 99 m Tc is used in the diagnosis of brain tumors, in studies of central and peripheral hemodynamics.

TECHNETIUM

TECHNETIUM (lat. Technetium, from the Greek technetos - artificial), Ts (read "technetium"), the first artificially obtained radioactive chemical element, atomic number 43. It has no stable isotopes. The longest-lived radioisotopes: 97 Tc (T 1/2 2.6 10 6 years, electron capture), 98 Tc (T 1/2 1.5 10 6 years) and 99 Tc (T 1/2 2.12 yrs) 10 5 years). Of practical importance is the short-lived nuclear isomer 99m Tc (T 1/2 6.02 hours).
The configuration of the two outer electron layers is 4s 2 p 6 d 5 5s 2 . Oxidation levels from -1 to +7 (valencies I-VII); the most stable +7. It is located in group VIIB in the 5th period of the Periodic Table of the Elements. The radius of the atom is 0.136 nm, the Tc 2+ ion is 0.095 nm, the Tc 4+ ion is 0.070 nm, and the Tc 7+ ion is 0.056 nm. Sequential ionization energies 7.28, 15.26, 29.54 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,9.
D. I. Mendeleev (cm. MENDELEEV Dmitry Ivanovich) when creating the periodic system, he left an empty cell in the table for technetium, a heavy analogue of manganese ("ecamarganese"). Technetium was obtained in 1937 by K. Perrier and E. Segré by bombarding a molybdenum plate with deuterons (cm. DEUTRON). In nature, technetium occurs in negligible amounts in uranium ores, 5·10 -10 g per 1 kg of uranium. Spectral lines of technetium have been found in the spectra of the Sun and other stars.
Technetium is isolated from a mixture of fission products 235 U - waste from the nuclear industry. During the processing of spent nuclear fuel, technetium is extracted by ion exchange, extraction and fractional precipitation methods. Technetium metal is obtained by reduction of its oxides with hydrogen at 500°C. World production of technetium reaches several tons per year. For research purposes, short-lived technetium radionuclides are used: 95m Тс( T 1/2 = 61 days), 97m Tc (T 1/2 = 90 days), 99m Tc.
Technetium - a silvery gray metal, with a hexagonal lattice, a=0.2737 nm, c= 0.4391 nm. Melting point 2200°C, boiling point 4600°C, density 11.487 kg/dm 3 . By chemical properties technetium is similar to rhenium. Values ​​of standard electrode potentials: Ts(VI)/Ts(IV) pairs 0.83 V, Ts(VII)/Ts(VI) pairs 0.65 V, Ts(VII)/Ts(IV) pairs 0.738 V.
When burning Tc in oxygen (cm. OXYGEN) yellow higher acid oxide Tc 2 O 7 is formed. Its solution in water is technetic acid NTSO 4 . When evaporated, dark brown crystals form. Salts of technetic acid - pertechnates (sodium pertechnate NaTcO 4 , potassium pertechnate KTcO 4 , silver pertechnate AgTcO 4). During the electrolysis of a solution of technetic acid, TcO 2 dioxide is released, which, when heated in oxygen, turns into Tc 2 O 7.
Interacting with fluorine, (cm. FLUORINE) Tc forms golden yellow crystals of technetium hexafluoride TcF 6 mixed with TcF 5 pentafluoride. Technetium oxyfluorides TcOF 4 and TcO 3 F were obtained. Chlorination of technetium gives a mixture of TcCl 6 hexachloride and TcCl 4 tetrachloride. Technetium oxychlorides TCO 3 Cl and TCOCl 3 have been synthesized. Sulfides are known (cm. SULFIDES) technetium Tc 2 S 7 and TcS 2 , carbonyl Tc 2 (CO) 10 . Tc reacts with nitrogen, (cm. NITRIC ACID) concentrated sulfuric (cm. SULFURIC ACID) acids and aqua regia (cm. AQUA REGIA). Pertechnates are used as corrosion inhibitors for mild steel. Isotope 99 m Tc is used in the diagnosis of brain tumors, in the study of central and peripheral hemodynamics (cm. HEMODYNAMICS).

encyclopedic Dictionary . 2009 .

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Table of nuclides General information Name, symbol Technetium 99, 99Tc Neutrons 56 Protons 43 Nuclide properties Atomic mass 98.9062547 (21) ... Wikipedia

- (symbol Tc), silver-gray metal, RADIOACTIVE ELEMENT. It was first obtained in 1937 by the bombardment of MOLYBDENUM nuclei with deuterons (the nuclei of DUTERIA atoms) and was the first element synthesized in a cyclotron. Technetium is found in foods... ... Scientific and technical encyclopedic dictionary

TECHNETIUM- artificially synthesized radioactive chem. element, symbol Tc (lat. Technetium), at. n. 43, at. m. 98.91. T. is obtained in sufficiently large quantities during the fission of uranium-235 in nuclear reactors; managed to get about 20 T isotopes. One of ... ... Great Polytechnic Encyclopedia

- (Technetium), Tc, artificial radioactive element of group VII of the periodic system, atomic number 43; metal. Received by Italian scientists C. Perrier and E. Segre in 1937 ... Modern Encyclopedia

- (lat. Technetium) Tc, a chemical element of group VII of the periodic system, atomic number 43, atomic mass 98.9072. Radioactive, the most stable isotopes are 97Tc and 99Tc (half-life, respectively, 2.6.106 and 2.12.105 years). First… … Big Encyclopedic Dictionary

- (lat. Technetium), Tc radioactive. chem. element of group VII periodic. Mendeleev's systems of elements, at. number 43, the first of artificially obtained chem. elements. Naib. long-lived radionuclides 98Tc (T1 / 2 = 4.2 106 years) and available in appreciable quantities ... ... Physical Encyclopedia

Exist., number of synonyms: 3 metal (86) ecamarganese (1) element (159) Dictionary of synonyms ... Synonym dictionary

Technetium- (Technetium), Tc, artificial radioactive element of group VII of the periodic system, atomic number 43; metal. Received by Italian scientists C. Perrier and E. Segre in 1937. ... Illustrated Encyclopedic Dictionary

43 Molybdenum ← Technetium → Ruthenium ... Wikipedia

- (lat. Technetium) Te, a radioactive chemical element of the VII group of the periodic system of Mendeleev, atomic number 43, atomic mass 98, 9062; metal, malleable and ductile. The existence of an element with atomic number 43 was ... ... Great Soviet Encyclopedia

Books

• Elements. A wonderful dream of Professor Mendeleev, Kuramshin Arkady Iskanderovich. What chemical element is named after goblins? How many times has technetium been "discovered"? What are "transfermium wars"? Why did even pundits once confuse manganese with magnesium and lead with ...

Here we must make a small, purely physical digression, otherwise it will not be clear why Segre needed this piece of molybdenum so much. Molybdenum was used to make the "tooth" of the deflecting plate of the world's first low-power cyclotron by today's standards. A cyclotron is a machine that accelerates the movement of charged particles, such as deuterons - the nuclei of heavy hydrogen, deuterium. The particles are accelerated by a high-frequency electric field in a spiral and with each turn they acquire more balls. Everyone who has ever worked on a cyclotron knows how difficult it is to conduct an experiment if the target is installed directly in the vacuum chamber of the cyclotron. It is much more convenient to work on the extracted beam, in a special chamber where all the necessary equipment can be placed. But getting the beam out of the cyclotron is far from easy. This is done using a special deflecting plate, to which a high voltage is applied. The plate is installed in the path of the accelerated particle beam and deflects it in the desired direction. Calculating the best plate configuration is a whole science. But despite the fact that the plates for cyclotrons are made and installed with maximum precision, its frontal part, or "tooth", absorbs about half of the accelerated particles. Naturally, the “tooth” is heated by blows, which is why it is now made of refractory molybdenum.

But it is also natural that the particles absorbed by the material of the tooth should cause in it nuclear reactions, more or less interesting for physicists. Segre believed that an extremely interesting nuclear reaction was possible in molybdenum, as a result of which element No. 43 (technetium), which had been opened many times and invariably “closed” before, could finally be truly discovered.

From Ilmenia to Masuria

Element number 43 was searched for a long time. And for a long time. They searched for it in ores and minerals, mainly manganese. Mendeleev, leaving an empty cell for this element in the table, called it ecamarganese. However, the first contenders for this cell appeared even before the discovery of the periodic law. In 1846, an analogue of manganese, ilmenium, was allegedly isolated from the mineral ilmenite. After ilmenium was “closed”, new candidates appeared: devy, lucium, nipponium. But they also turned out to be “false elements”. The forty-third cell of the periodic table continued to be empty.

In the 1920s, the problem of ecamarganese and dvimarganese (eka means "one", dvi - "two"), i.e. elements No. 43 and 75, was taken up by the excellent experimenters spouses Ida and Walter Noddak. Having traced the patterns of changes in the properties of elements by groups and periods, they came to the seemingly seditious, but essentially correct idea that the similarity of manganese and its eka- and dvi-analogues is much less than previously thought, that it is more reasonable to look for these elements not in manganese ores, and in crude platinum and in molybdenum ores.

The experiments of the Noddaks continued for many months. In 1925, they announced the discovery of new elements - masuria (element No. 43) and rhenium (element No. 75). The symbols of the new elements occupied the empty cells of the periodic table, but later it turned out that only one of the two discoveries had actually taken place. For masuria, Ida and Walter Noddak took impurities that have nothing to do with element No. 43 technetium.

The symbol Ma stood in the table of elements for more than 10 years, although back in 1934 two theoretical works appeared that stated that element No. 43 could not be found either in manganese, or in platinum, or in any other ores. It's about about the prohibition rule formulated almost simultaneously by the German physicist G. Mattauch and the Soviet chemist S. A. Shchukarev.

Technetium - "Forbidden" element and nuclear reactions

Soon after the discovery of isotopes, the existence of isobars was also established. Note that isobar and isobar are concepts as distant as decanter and countess. Isobars are called atoms with the same mass numbers belonging to different elements. Example of several isobars: 93 Zr, 93 Nb, 93 Mo.

The meaning of the Mattauch-Shchukarev rule is that stable isotopes with odd numbers cannot have stable isobars. So, if the isotope of element No. 41 niobium-93 is stable, then the isotopes of neighboring elements - zirconium-93 and molybdenum-93 - must necessarily be radioactive. The rule applies to all elements, including element number 43.

This element is located between molybdenum (atomic mass 95.92) and ruthenium (atomic mass 101.07). Therefore, the mass numbers of the isotopes of this element should not go beyond the range of 96-102. But all stable "vacancies" of this range are occupied. Molybdenum has stable isotopes with mass numbers 96, 97, 98 and 100, while ruthenium has 99, 101, 102 and some others. This means that element 43 cannot have a single non-radioactive isotope. However, it does not at all follow from this that it cannot be found in the earth's crust: there are radium, uranium, and thorium.

Uranium and thorium have survived on the globe thanks to the long lifetimes of some of their isotopes. Other radioactive elements are products of their radioactive decay. Element 43 could only be detected in two cases: either if it has isotopes whose half-life is measured in millions of years, or if its long-lived isotopes are formed (and often enough) from the decay of elements 90 and 92.

Segre did not count on the first: if there were long-lived isotopes of element No. 43, they would have been found earlier. The second is also unlikely: most thorium and uranium atoms decay by emitting alpha particles, and the chain of such decays ends with stable isotopes of lead, an element with atomic number 82. Lighter elements cannot be formed during the alpha decay of uranium and thorium.

True, there is another type of decay - spontaneous fission, in which heavy nuclei spontaneously divide into two fragments of approximately the same mass. In the spontaneous fission of uranium, the nuclei of element No. 43 could be formed, but there would be very few such nuclei: on average, one uranium nucleus out of two million spontaneously fissions, and out of a hundred acts of spontaneous fission of uranium nuclei, element No. 43 is formed only in two. However, this Emilio Segre did not know then. Spontaneous fission was discovered only two years after the discovery of element No. 43.

Segre was carrying a piece of irradiated molybdenum across the ocean. But there was no certainty that a new element would be found in it, and it could not be. There were “for”, there were “against”.

Falling on a molybdenum plate, a fast deuteron penetrates quite deeply into its thickness. In some cases, one of the deuterons can merge with the nucleus of the molybdenum atom. For this, first of all, it is necessary that the energy of the deuteron is sufficient to overcome the forces of electrical repulsion. And this means that the cyclotron must accelerate the deuteron to a speed of about 15 thousand km/sec. The compound nucleus formed by the fusion of a deuteron and a molybdenum nucleus is unstable. It must get rid of excess energy. Therefore, as soon as the fusion has taken place, a neutron flies out of such a nucleus, and the former nucleus of the molybdenum atom turns into the nucleus of the atom of element No. 43.

Natural molybdenum consists of six isotopes, which means that, in principle, the irradiated piece of molybdenum could contain atoms of six isotopes of the new element. This is important because some isotopes can be short-lived and therefore chemically elusive, especially since more than a month has passed since the irradiation. But other isotopes of the new element could "survive". It was them that Segre hoped to discover. On this, in fact, all the "for" ended. "Against" was much more.

Ignorance of the half-lives of the isotopes of element 43 worked against the researchers. It could also happen that not a single isotope of element 43 exists for more than a month. The researchers also worked against "accompanying" nuclear reactions, in which radioactive isotopes of molybdenum, niobium and some other elements were formed.

It is very difficult to isolate the minimum amount of an unknown element from a radioactive multicomponent mixture. But that was exactly what Segre and his few assistants were to do.

Work began on January 30, 1937. First of all, they found out what particles emitted by molybdenum, which had been in the cyclotron and crossed the ocean. It emitted beta particles - fast nuclear electrons. When about 200 mg of irradiated molybdenum was dissolved in aqua regia, the beta activity of the solution was about the same as that of several tens of grams of uranium.

Previously unknown activity was discovered, it remained to determine who was its "culprit". First, radioactive phosphorus-32, formed from impurities that were in molybdenum, was chemically isolated from the solution. Then the same solution was subjected to "cross-examination" on the row and column of the periodic table. Carriers of unknown activity could be isotopes of niobium, zirconium, rhenium, ruthenium, molybdenum itself, finally. Only by proving that none of these elements is involved in the emitted electrons, it was possible to speak about the discovery of element No. 43.

Two methods were used as the basis for the work: one is a logical method of elimination, the other is the “carrier” method widely used by chemists to separate mixtures, when a compound of this element or another with similar chemical properties. And if the carrier substance is removed from the mixture, it carries away "related" atoms from there.

First of all, niobium was excluded. The solution was evaporated and the resulting precipitate was redissolved, this time in potassium hydroxide. Some elements remained in the undissolved part, but unknown activity passed into solution. And then potassium niobate was added to it, so that the stable niobium would “take away” the radioactive one. Unless, of course, he was present in the solution. Niobium is gone - activity remains. Zirconium was subjected to the same test. But the zirconium fraction was also inactive. Molybdenum sulfide was then precipitated, but the activity still remained in solution.

After that, the most difficult thing began: it was necessary to separate the unknown activity and rhenium. After all, the impurities contained in the material of the “tooth” could turn not only into phosphorus-32, but also into radioactive isotopes of rhenium. It seemed all the more likely that it was the rhenium compound that carried the unknown activity out of the solution. And as the Noddacks found out, element number 43 should be more like rhenium than manganese or any other element. To separate the unknown activity from rhenium meant finding a new element, because all other "candidates" had already been rejected.

Emilio Segre and his closest assistant Carlo Perrier were able to do it. They found that in hydrochloric acid solutions (0.4-5 normal) a carrier of unknown activity precipitates when hydrogen sulfide is passed through the solution. But at the same time, rhenium also falls out. If the precipitation is carried out from a more concentrated solution (10-normal), then rhenium precipitates completely, and the element carrying an unknown activity, only partially.

Finally, for control, Perrier set up experiments to separate a carrier of unknown activity from ruthenium and manganese. And then it became clear that beta particles can only be emitted by the nuclei of a new element, which was called technetium (from the Greek "artificial").

These experiments were completed in June 1937. Thus, the first of the chemical "dinosaurs" was recreated - elements that once existed in nature, but completely "extinct" as a result of radioactive decay.

Later, extremely small amounts of technetium, formed as a result of spontaneous fission of uranium, were found in the earth. The same, by the way, happened with neptunium and plutonium: at first, the element was obtained artificially, and only then, having studied it, they managed to find it in nature.

Now technetium is obtained from fission fragments of uranium-35 in nuclear reactors.. True, it is not easy to separate it from the mass of fragments. There are about 10 g of element No. 43 per kilogram of fragments. This is mainly the technetium-99 isotope, whose half-life is 212 thousand years. Thanks to the accumulation of technetium in reactors, it was possible to determine the properties of this element, obtain it in its pure form, and study quite a few of its compounds. In them, technetium exhibits valence 2+, 3+ and 7+. Just like rhenium, technetium is a heavy metal (density 11.5 g/cm3), refractory (melting point 2140°C), and chemically resistant.

Despite the fact that technetium- one of the rarest and most expensive metals (much more expensive than gold), it has already brought practical benefits.

The damage caused to humanity by corrosion is enormous. On average, every tenth blast furnace works to “cover costs” from corrosion. There are substances-inhibitors that slow down the corrosion of metals. The best inhibitors were pertechnates - salts of technetic acid HTcO 4 . The addition of one ten-thousandth mole of TcO 4 -

prevents corrosion of iron and mild steel - the most important structural material.

The widespread use of pertechnates is hampered by two circumstances: the radioactivity of technetium and its high cost. This is especially annoying because similar compounds of rhenium and manganese do not prevent corrosion.

Item #43 has another unique property. The temperature at which this metal becomes a superconductor (11.2 K) is higher than that of any other pure metal. True, this figure was obtained on samples not very high purity- only 99.9%. Nevertheless, there are reasons to believe that alloys of technetium with other metals will turn out to be ideal superconductors. (As a rule, the temperature of transitions to the state of superconductivity for alloys is higher than for commercially pure metals.)

Although not so utilitarian, but useful service was rendered by technetium and astronomers. Technetium was discovered by spectral methods on some stars, for example, on the star and the constellation Andromeda. Judging by the spectra, element No. 43 is as common there as zirconium, niobium, molybdenum, and ruthenium. This means that the synthesis of elements in the Universe continues even now.

Technetium (lat. Technetium), Tc, a radioactive chemical element of group VII of the Mendeleev periodic system, atomic number 43, atomic mass 98, 9062; metal, malleable and ductile.

Technetium has no stable isotopes. Of the radioactive isotopes (about 20), two are of practical importance: 99 Tc and 99m Tc with half-lives, respectively T 1/2= 2.12 × 10 5 years and T 1/2 = 6,04 h. In nature, the element is in small quantities - 10 -10 G in 1 t uranium resin.

Physical and chemical properties.

Powdered metal technetium is gray in color (reminiscent of Re, Mo, Pt); compact metal (molten metal ingots, foil, wire) of silver-gray color. Technetium in the crystalline state has a close-packed hexagonal lattice ( a = 2,735

, c = 4.391); in thin layers (less than 150 ) - a cubic face-centered lattice ( a = 3.68? 0.0005); density T. (with a hexagonal lattice) 11.487 g / cm 3, t pl 2200? 50?С; t kip 4700? С; electrical resistivity 69 * 10 -6 ohm×cm(100? C); temperature of transition to the state of superconductivity Tc 8.24 K. Technetium is paramagnetic; its magnetic susceptibility at 25 0 C - 2.7 * 10 -4 . The configuration of the outer electron shell of the atom Tc 4 d 5 5s 2 ; atomic radius 1.358; ionic radius Tc 7+ 0.56.

By chemical properties Tc is close to Mn and especially to Re, in compounds it exhibits oxidation states from -1 to +7. The most stable and well-studied compounds are Tc in the +7 oxidation state. When Technetium or its compounds interact with oxygen, oxides Tc 2 O 7 and TcO 2 are formed, with chlorine and fluorine - halides TcX 6, TcX 5, TcX 4, the formation of oxyhalides, for example TcO 3 X (where X is a halogen), with sulfur - sulfides Tc 2 S 7 and TcS 2 . Technetium also forms technetic acid HTcO 4 and its salts pertechnate MeTcO 4 (where Me is a metal), carbonyl, complex and organometallic compounds. In the series of voltages, Technetium is to the right of hydrogen; he does not respond to hydrochloric acid any concentration, but easily soluble in nitric and sulfuric acids, aqua regia, hydrogen peroxide, bromine water.

Receipt.

The main source of technetium is waste from the nuclear industry. The yield of 99 Tc in the fission of 235 U is about 6%. Technetium in the form of pertechnates, oxides, sulfides is extracted from a mixture of fission products by extraction with organic solvents, ion exchange methods, and precipitation of sparingly soluble derivatives. The metal is obtained by reduction with hydrogen NH 4 TcO 4 , TcO 2 , Tc 2 S 7 at 600-1000 0 C or by electrolysis.

Application.

Technetium is a promising metal in technology; it can find application as a catalyst, high temperature and superconducting material. Technetium compounds. - effective corrosion inhibitors. 99m Tc is used in medicine as a source of g-radiation . Technetium is radiation-hazardous; working with it requires special sealed equipment.

Discovery history.

Back in 1846, the chemist and mineralogist R. Herman, who worked in Russia, found in the Ilmensky mountains in the Urals a previously unknown mineral, which he called yttroilmenite. The scientist did not rest on his laurels and tried to isolate from it a new chemical element, which, as he believed, was contained in the mineral. But he did not have time to open his ilmenium, as the famous German chemist G. Rose, "closed" it, proving the fallacy of Herman's work.

A quarter of a century later, ilmenium reappeared at the forefront of chemistry - it was remembered as a contender for the role of "eka - manganese", which was supposed to take the empty place in the periodic table at number 43. But the reputation of ilmenium was greatly "tarnished" by the works of G. Rose, and, despite the fact that many of its properties, including atomic weight, were quite suitable for element No. 43, D. I. Mendeleev did not register it in his table. Further research finally convinced the scientific world that , that ilmenium can enter the history of chemistry only with the sad glory of one of the many false elements.

Since a holy place is never empty, claims for the right to occupy it appeared one after another. Davy, lucius, nipponium - they all burst, as if bubble, barely having time to appear.

But in 1925, the German scientists Ida and Walter Noddak published a message that they had discovered two new elements - masurium (No. 43) and rhenium (No. 75). For rhenium, fate turned out to be favorable: he was immediately legitimized in his rights and immediately occupied the residence prepared for him. But fortune turned its back on Masurium: neither its discoverers nor other scientists could scientifically confirm the discovery of this element. True, Ida Noddack stated that “soon, masurium, like rhenium, can be bought in stores,” but chemists, as you know, do not believe the words, and the Noddak spouses could not provide other, more convincing evidence - the list of “false forty-thirds” filled with another loser.

During this period, some scientists began to lean towards the idea that far from all the elements predicted by Mendeleev, in particular element No. 43, exist in nature. Maybe they simply do not exist and there is no need to waste time and break spears? Even the prominent German chemist Wilhelm Prandtl, who vetoed the discovery of masurium, came to this conclusion.

The younger sister of chemistry, nuclear physics, which had already gained a strong authority by that time, made it possible to clarify this issue. One of the laws of this science (noted in the 1920s by the Soviet chemist S. A. Shchukarev and finally formulated in 1934 by the German physicist G. Mattauch) is called the Mattauch-Shchukarev rule, or the rule of prohibition.

Its meaning lies in the fact that in nature there cannot be two stable isobars, the nuclear charges of which differ by one. In other words, if any chemical element has a stable isotope, then its closest neighbors in the table are "categorically forbidden" to have a stable isotope with the same mass number. In this sense, element No. 43 is clearly unlucky: its neighbors on the left and right - molybdenum and ruthenium - made sure that all the stable vacancies of the nearby "territories" belonged to their isotopes. And this meant that element No. 43 had a heavy fate: no matter how many isotopes it had, they were all doomed to instability, and thus they had to continuously - day and night - decay, whether they wanted to or not.

It is reasonable to assume that once element number 43 existed on Earth in appreciable quantities, but gradually disappeared like morning fog. So why, in this case, uranium and thorium have survived to this day? After all, they are also radioactive and, therefore, from the very first days of their lives, decay, as they say, slowly but surely? But this is precisely the answer to our question: uranium and thorium survived only because they decay slowly, much more slowly than other elements with natural radioactivity (and yet, during the existence of the Earth, uranium reserves in its natural stores decreased by about a hundred once). Calculations by American radiochemists have shown that an unstable isotope of one or another element has a chance to survive in the earth's crust from the moment of the "creation of the world" to the present day only if its half-life exceeds 150 million years. Looking ahead, let's say that when various isotopes of element No. 43 were obtained, it turned out that the half-life of the longest-lived of them was only a little more than two and a half million years, and, therefore, its last atoms ceased to exist, apparently, even long before the appearance on Earth first dinosaur: after all, our planet "functions" in the universe for about 4.5 billion years.

Therefore, if scientists wanted to “feel” element No. 43 with their own hands, it had to be created with the same hands, since nature had long ago included it in the lists of the missing. But is science capable of such a task?

Yes, on the shoulder. This was first experimentally proved back in 1919 by the English physicist Ernest Rutherford. He subjected the nucleus of nitrogen atoms to a fierce bombardment, in which the decaying radium atoms served as weapons all the time, and the alpha particles formed in the process served as projectiles. As a result of a long shelling, the nuclei of nitrogen atoms were replenished with protons and it turned into oxygen.

Rutherford's experiments armed scientists with extraordinary artillery: with its help it was possible not to destroy, but to create - to turn one substance into another, to obtain new elements.

So why not try to extract element number 43 in this way? The young Italian physicist Emilio Segre took up the solution of this problem. In the early 1930s he worked at the University of Rome under the already famous Enrico Fermi. Together with other "boys" (as Fermi jokingly called his talented students) Segre took part in experiments on the neutron irradiation of uranium, and solved many other problems of nuclear physics. But then the young scientist received a tempting offer - to head the Department of Physics at the University of Palermo. When he arrived in the ancient capital of Sicily, he was disappointed: the laboratory, which he was to lead, was more than modest and its appearance was by no means conducive to scientific exploits.

But great was Segre's desire to penetrate deeper into the mysteries of the atom. In the summer of 1936, he crosses the ocean to visit the American city of Berkeley. Here, in the radiation laboratory of the University of California, the cyclotron invented by Ernest Lawrence, an accelerator of atomic particles, has been operating for several years. Today, this small device would seem to physicists as something like a child's toy, but at that time the world's first cyclotron aroused the admiration and envy of scientists from other laboratories (in 1939, E. Lawrence was awarded the Nobel Prize for its creation).

Task 1.Write the electronic formula of the technetium atom. How many electrons are in the d-sublevel of the penultimate electron layer? Which electron family does the element belong to?

Decision: The Tc atom in the periodic table has the serial number 43. Therefore, its shell contains 43 electrons. In the electronic formula, we distribute them into sublevels according to the filling order (in accordance with the Klechkovsky rules) and taking into account the capacity of the sublevels: Tc 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 5 5s 2 . The order in which the sublevels are filled is as follows: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d. The last electron is located on the 4d sublevel, which means that technetium belongs to the d-element family. There are 5 electrons on the d-sublevel of the penultimate (4th) layer.

Answer: 5d.

Task 2.Which element atom has the electronic configuration 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 1 ?

Decision:

The number of electrons in the shell of a neutral atom is 49. Therefore, its nuclear charge and, therefore, its serial number are also 49. In the periodic system of D.I. Mendeleev, we find that this element is indium.

Task 3.Which of the following compounds has the least acidic properties? a) HNO 3, b) H 3 PO 4, c) H 3 AsO 4, d) H 3 SbO 4.

Decision:

The given oxygen-containing compounds are hydroxides of elements of the main subgroup of group V of the periodic table. It is known that the acidic properties of hydroxides weaken from top to bottom in a subgroup. Therefore, in this series, H 3 SbO 4 has the least pronounced acidic properties.

Answer: H 3 SbO 4.

Task 4.Specify the type of hybridization of boron orbitals in the BBr 3 molecule.

Decision:

The formation of three covalent bonds between boron and bromine atoms involves one s- and two p-orbitals of the boron atom, the properties of which differ. Since all chemical bonds in the BBr 3 molecule are equivalent, the boron atom undergoes hybridization. The above three orbitals of the outer electron layer take part in it. Therefore, the type of hybridization is sp 2 .

Answer: sp2.

Task 5.According to the periodic table, make an empirical formula for the highest oxide of lead. What is its molar mass?

Decision:

Lead is in the 4th group of the periodic table, so its highest oxidation state is +4. The oxygen atom in oxides has an oxidation state of -2, so there are two oxygen atoms for every lead atom in the oxide molecule. The formula of the highest oxide is PbO 2. Let's calculate its molar mass: 207+2 16=239.

Answer: 239 g/mol.

Task 6.What types of chemical bonds are present in the NH 4 I molecule?

Decision:

The NH 4 I molecule consists of NH 4 + and I - ions, between which there is an ionic bond. In the NH 4 + ion, four bonds are polar covalent, and one of them is formed according to the donor-acceptor type (see Section 3.2.3).

Answer: ionic, covalent polar, donor-acceptor.

Task 7.Bond Energy Calculation.

Compute Energy H-S connections in the H 2 S molecule according to the following data: 2H 2 (g) + S 2 (g) \u003d 2 H 2 S (g) - 40.30 kJ; the bond energies D(H-H) and D(S-S) are –435.9 kJ/mol and –417.6 kJ/mol, respectively.

Decision: The formation of two H 2 S molecules can be represented as a sequential process of bond breaking H-H in a molecule H2 and connections S-S in a molecule S2:

2 H-H 4 H - 2D(H-H)

S-S 2 S-D(S-S)

4 H + 2 S 2 H 2 S+ 4D(S-H),

where D(H-H), D(S-S) and D(S-H) - bonding energy H-H, S-S and S-H respectively. Summing up the left and right parts of the above equations, we arrive at the thermochemical equation

2H 2 (g) + S 2 (g) \u003d 2 H 2 S (g) -2D (H-H) - D (S-S) + 4D (S-H).

The thermal effect of this reaction is

Q \u003d -2D (H-H) - D (S-S) + 4D (S-H), where D(S-H)= .

Task 8.Calculation of the bond length.

Calculate the bond length in the HBr molecule if the internuclear distance in the H 2 and Br 2 molecules is 0.74∙10 -10 and 2 ,28 ∙10 -10 m respectively.

Decision: The length of a covalent bond between two unlike atoms is equal to the sum of their covalent radii

l(H-Br) = r(H) + r(Br).

In turn, the covalent radius of an atom is defined as half the internuclear distance in molecules H 2 and Br2:

Thus,

Answer: 1.51 10 -10 m.

Task 9.Determination of the type of hybridization of orbitals and the spatial structure of the molecule.

What type of hybridization of electron clouds takes place in the silicon atom during the formation of the SiF 4 molecule? What is the spatial structure of this molecule?

Decision: In the excited state, the structure of the external energy level of the silicon atom is as follows:

3s		3p
3s	3p x	3py	3pz

In the formation of chemical bonds in the silicon atom, electrons of the third energy level participate: one electron in the s-state and three electrons in the p-state. When a SiF 4 molecule is formed, four hybrid electron clouds (sp 3 hybridization) arise. The SiF 4 molecule has a spatial tetrahedral configuration.

Task 10.Determination of the valencies of elements in chemical compounds based on the analysis of graphic electronic formulas of the ground and excited states of atoms of these elements.

What valency, due to unpaired electrons, can sulfur exhibit in the ground and in the excited state?

Decision: The distribution of electrons of the external energy level of sulfur …3s 2 3p 4, taking into account the Hund rule, has the form:

	s		p				d
16S

From the analysis of the ground and two excited states, it follows that the valency (spinvalence) of sulfur in the normal state is two, in the first excited state - four, in the second - six.

Options control tasks

Option 1

1. What information about an element can be learned based on its position in the PSE?

2. Write the electronic formulas of the atoms of elements with atomic numbers 9 and 28. Show the distribution of the electrons of these atoms in quantum cells. Which electronic family does each of these elements belong to?

Option 2

1. Give definitions: ionization energy, electron affinity and electronegativity of an atom? How do they change in period and group?

2. Write the electronic formulas of the atoms of elements with serial numbers 16 and 26. Distribute the electrons of these atoms among the quantum cells. Which electronic family does each of these elements belong to?

Option 3

1. Which covalent bond is called polar and which is non-polar? What is the quantitative measure of the polarity of a covalent bond?

2. What is the maximum number of electrons that can occupy s-, p-, d- and f-orbitals of the given energy level? Why? Write the electronic formula of an atom of an element with atomic number 31.

Option 4

1. How the valence bond (BC) method explains linear structure BeCl 2 molecules?

4s or 3d; 5s or 4p? Why? Write the electronic formula of an atom of an element with atomic number 21.

Option 5

1. What bond is called σ-bond and what π-bond?

2. Which orbitals of the atom are filled with electrons earlier: 4d or 5s; 6s or 5p? Why? Write the electronic formula of an atom of an element with atomic number 43.

Option 6

1. What is called a dipole moment?

2. Write the electronic formulas of atoms of elements with serial numbers 14 and 40. How many free 3d-orbitals of the atoms of the last element?

Option 7

1. What chemical bond is called ionic? What is the mechanism of its formation?

2. Write the electronic formulas of atoms of elements with serial numbers 21 and 23. How many free 3d-orbitals in the atoms of these elements?

Option 8

1. Which variant of the periodic system is most widely used and why?

2. How many free d- orbitals are found in atoms Sc, Ti, V? Write the electronic formulas of the atoms of these elements.

Option 9

1. What properties of an ionic bond distinguish it from a covalent bond?

2. Using Hund's rule, distribute electrons among quantum cells corresponding to the lowest energy state of atoms: chromium, phosphorus, sulfur, germanium, nickel.

2. For a boron atom, two different electronic states are possible and . What are these states called? How to move from the first state to the second?

Option 11

1. Which of the 4 different types of atomic orbitals have the most complex formula?

2. Which atom of the elements corresponds to each of the following electronic formulas:

a) ;b) ;

Option 12

2. Using Hund's rule, distribute electrons among quantum cells corresponding to the highest energy state of atoms: manganese, nitrogen, oxygen, silicon, cobalt.

Option 13

1. If there are 4 electrons in the p-orbitals of any layer, how many of them have unpaired spins and what is their total spin number 7

2. Atoms of what elements and what states of these elements correspond to the following electronic formulas and ; and ?

Option 14

1. What characteristics of an atom can be called, knowing: a) the serial number of the element in the periodic system; b) period number; c) the number and type of the group in which the element is located?

2. Write the electronic configuration of atoms using the electronic formulas for elements with serial numbers 12, 25, 31, 34, 45.

Option 15

1. How to determine, based on the position of an atom in the periodic system, the number of elementary particles in its composition? Determine the number of elementary particles in the composition of sulfur and zinc atoms.

2. Using Hund's rule, distribute the electrons among the energy cells corresponding to the lowest energy state for the atoms of elements with serial numbers 26, 39, 49, 74, 52.

Option 16

1. What are quantum numbers? What properties of orbitals and electrons do they reflect? What values ​​do they take? Determine the maximum possible number of electrons in each energy level of aluminum and copper atoms.

2. Which of the electronic formulas reflecting the structure of an unexcited atom of some element is incorrect: a) 1s 2 2s 2 2p 5 3s 1 ; b) 1s 2 2s 2 2p 6; in) 1s 2 2s 2 2p 6 3s 2 3p 6 3d 4 ; G) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2; e) 1s 2 2s 2 2p 6 3s 2 3d 2 ? Why? Atoms of which elements correspond to correctly composed electronic formulas?

Option 17

1. What principles underlie all modern theories of chemical bonding? What is an ionic bond? What properties does it have? Give examples of compounds with an ionic bond.

2. Write the electronic formulas of the atoms of elements with serial numbers 24 and 33, given that the first one has a “failure” of one 4s-electron to the 3d sublevel. What is the maximum spin d-electrons at the atoms of the first and p-electrons from the atoms of the second element?

Option 18

1. What is electronegativity? How does electronegativity change? R-elements in a period, in a group of the periodic system with increasing atomic number? Why?

2. Make electronic formulas of atoms of elements with serial numbers 32 and 42, given that the latter has a “failure” of one 5s-electron on 4d-sublevel. Which electronic family does each of these elements belong to?

Option 19

1. What values ​​can quantum numbers take n, l, m l and m S characterizing the state of electrons in an atom? What values ​​do they take for the outer electrons of the magnesium atom?

2. How many free f-orbitals is contained in the atoms of elements with serial numbers 61, 62, 91, 92? Using Hund's rule, distribute the electrons among the energy cells for the atoms of these elements.

Option 20

1. What is ionization energy? In what units is it expressed? How does recovery activity change? s- and p-elements in groups of the periodic system with increasing atomic number? Why?

2. What is the Pauli principle? Can it be at some sublevel of the atom p 7 - or d 12- electrons? Why? Compose the electronic formula of an atom of an element with serial number 22 and indicate its valence electrons. .

Option 21

1. List the rules according to which orbitals are filled with electrons. What is the electronic formula of an atom? Write the electronic formulas for silicon and iron, underlining the valence electrons.

2. Quantum numbers for electrons of the outer energy level of atoms of some elements have the following values: n = 4; l = 0; m l= 0; m S= . Write the electronic formulas of the atoms of these elements and determine how many free 3d-orbitals contains each of them.

Option 22

1. What are isotopes? How can one explain that for most elements of the periodic system, atomic masses are expressed as a fractional number? Can atoms of different elements have the same mass? What are these atoms called?

2. Based on the position of the metal in the periodic system, give a reasoned answer to the question: which of the two hydroxides is the stronger base: Ba (OH) 2 or Mg (OH) 2; Ca(OH) 2 or Fe(OH) 2; Cd (OH) 2 or Sr (OH) 2?

Option 23

1. What is electron affinity? In what units is it expressed? How does the oxidative activity of non-metals change in a period and in a group of the periodic system with an increase in the serial number? Justify your answer by the structure of the atom of the corresponding element.

2. Manganese forms compounds in which it exhibits an oxidation state of +2, +3, +4, +6, +7. Write formulas for its oxides and hydroxides corresponding to these oxidation states. Write the reaction equations proving the amphoteric nature of manganese (IV) hydroxide.

Option 24

1. How do the acid-base and redox properties of higher oxides and hydroxides of elements change with an increase in the charge of their nuclei: a) within a period; b) within a subgroup.

2. How many and what values ​​​​can the magnetic quantum number take m l at orbital number l= 0, 1, 2 and 3? What elements in the periodic system are called s-, p-, d- and f-elements? Give examples.

Option 25

1. Theory of hybridization. The mechanism of formation of the donor-acceptor bond. Connection examples

2. Which one R-elements of the fifth group of the periodic system - phosphorus or antimony - are non-metallic properties more pronounced? Which of the hydrogen compounds of these elements is the strongest reducing agent? Justify your answer by the structure of the atom of these elements.

Option 26

1. What is the lowest oxidation state of chlorine, sulfur, nitrogen and carbon? Why? Write formulas for aluminum compounds with these elements in this oxidation state. What are the names of the corresponding compounds?

2. The energy state of the outer electron of an atom is described the following values quantum numbers: n=4, l=0, m l=0. The atoms of which elements have such an electron? Compose the electronic formulas of the atoms of these elements. Write down all the quantum numbers of ale electrons of atoms: a) lithium, beryllium, carbon; b) nitrogen, oxygen, fluorine.

Option 27

1. Metal connection. Formation mechanism and properties. Examples of compounds and their properties.

2. Based on the position of germanium and technetium in the periodic system, write the formulas for meta- and orthogermanic acids, and technetium oxide, corresponding to their highest oxidation state. Draw the formulas of these compounds graphically.

Option 28

1. Which element of the fourth period - chromium or selenium - has more pronounced metallic properties? Which of these elements forms a gaseous combination with hydrogen? Motivate your answer by the structure of the atoms of chromium and selenium.

2. The nickel-57 isotope is formed by bombarding the nuclei of iron-54 atoms with α-particles. Make an equation for this nuclear reaction and write it in abbreviated form

Option 29

Write the electronic formulas of atoms of elements and name them if the values ​​of quantum numbers ( n, l, m l , m S) electrons of the outer (last) and penultimate electron layers are as follows:

a) 6, 0, 0, +; 6, 0, 0, - ; 6, 1, -1, + ;

b) 3, 2, -2, +; 3, 2, -1, + ; 4, 0, 0, +; 4, 0, 0, -.

Option 30

1. Modern methods describing the formation of a covalent bond, their main postulates. Properties of a covalent bond. Give examples of compounds with a covalent bond and their properties.

2. Compose comparative characteristic elements with serial numbers 17 and 25 based on their position in the PSE. Explain the reasons for the similarities and differences in the properties of these elements.

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