Isotopes of gold. Gold from a nuclear reactor

09.05.2019

In 1935, the American physicist Arthur Dempster succeeded in carrying out the mass spectrographic determination of the isotopes contained in natural uranium. During the experiments, Dempster also studied the isotopic composition of gold and found only one isotope - gold-197. There was no indication of the existence of gold-199. Some scientists have suggested that there must be a heavy isotope of gold, because gold at that time was attributed to a relative atomic mass of 197.2. However, gold is a monoisotopic element. Therefore, those who want to artificially obtain this coveted noble metal, all efforts must be directed to the synthesis of the only stable isotope - gold-197.

The news of successful experiments in the manufacture of artificial gold has always caused concern in the financial and government circles. It was so in the days of the Roman rulers, and it remains so now. Therefore, it is not surprising that the dry report on the research of the National Laboratory in Chicago by the group of Professor Dempster has recently caused excitement in the capitalist financial world: in an atomic reactor you can get gold from mercury! This is the most recent and convincing case of alchemical transformation.

It began back in 1940, when in some laboratories of nuclear physics they began to bombard the elements neighboring with gold with fast neutrons obtained with the help of a cyclotron - mercury and platinum. At a meeting of American physicists in Nashville in April 1941, A. Sherr and C. T. Bainbridge of Harvard University reported on the successful results of such experiments. They sent overclocked deuterons at a lithium target and received a stream of fast neutrons, which was used to bombard mercury nuclei. As a result of nuclear transformation, gold was obtained!

Three new isotopes with mass numbers 198, 199 and 200. However, these isotopes were not as stable as the natural isotope - gold-197. Emitting beta rays, after a few hours or days they again turned into stable isotopes of mercury with mass numbers 198, 199 and 200. Consequently, the modern adherents of alchemy had no reason to rejoice. Gold, which turns back into mercury, is worthless: it is deceptive gold. However, scientists rejoiced at the successful transformation of the elements. They were able to expand their knowledge of artificial isotopes of gold.

The “transmutation” carried out by Sherr and Bainbridge is based on the so-called (n, p) -reaction: the nucleus of a mercury atom, absorbing a neutron n, turns into a gold isotope, and the proton p is released.

Natural mercury contains seven isotopes in varying amounts: 196 (0.146%), 198 (10.02%), 199 (16.84%), 200 (23.13%), 201 (13.22%), 202 (29 , 80%) and 204 (6.85%). Since Sherr and Bainbridge found isotopes of gold with mass numbers 198, 199 and 200, it should be assumed that the latter arose from isotopes of mercury with the same mass numbers. For example: 198 Hg + n = 198 Au + p

This assumption seems justified - after all, these isotopes of mercury are quite common. The probability of any nuclear reaction occurring is determined primarily by the so-called effective capture cross section of an atomic nucleus in relation to the corresponding bombarding particle. Therefore, the collaborators of Professor Dempster, physicists Ingram, Hess and Haydn, tried to accurately determine the effective cross section for neutron capture by natural isotopes of mercury. In March 1947, they were able to show that isotopes with mass numbers 196 and 199 have the largest neutron capture cross section and therefore have the highest probability of converting to gold. As a "by-product" of their experimental research, they received ... gold! Exactly 35 μg obtained from 100 mg of mercury after irradiation with moderated neutrons in a nuclear reactor. This amounts to a yield of 0.035%, but if the found amount of gold is attributed only to mercury-196, then a solid yield of 24% will be obtained, because gold-197 is formed only from the isotope of mercury with a mass number of 196.

(N, p) -reactions often occur with fast neutrons, and predominantly (n, y) -conversions with slow neutrons. The gold discovered by Dempster's employees was formed as follows:

196 Hg + n = 197 Hg * + y

197 Hg * + e- = 197 Au

The unstable mercury-197 formed by the (n, y) -process turns into stable gold-197 as a result of K-capture (an electron from the K-shell of its own atom). Thus, Ingram, Hess and Haydn synthesized tangible amounts of artificial gold in an atomic reactor! Despite this, their gold synthesis did not alarm anyone, since only scientists who carefully followed the publications in the Physicl Review learned about it. The report was short and probably not interesting enough for many because of its unremarkable title: "Neutron cross-sections for mercury isotopes" (Effective cross sections for neutron capture by isotopes of mercury). However, the occasion pleased that two years later, in 1949, an overly zealous journalist picked up this purely scientific message and, in a loud-market manner, announced in the world press about the production of gold in a nuclear reactor. Following this, there was a major confusion in France with the quotation of gold on the stock exchange, and a collapse began. It seemed that events were developing exactly as Rudolph Dauman imagined, predicting in his science fiction novel "THE END OF GOLD".

However, artificial gold obtained in an atomic reactor was long in coming. It had no intention of flooding the markets of the world. By the way, Professor Dempster had no doubts about it. Gradually, the French capital market calmed down again. This is not the last merit of the French magazine Atoms, which in the January 1950 issue published an article: "La transmutation du mercure en or" (Transmutation of mercury into gold).

Although the magazine, in principle, recognized the possibility of obtaining gold from mercury by the nuclear reaction method, however, it assured its readers the following: the price of such an artificial noble metal would be many times higher than natural gold mined from the poorest gold ores!

Dempster's employees could not deny themselves the pleasure of getting a certain amount of such artificial gold in the reactor. Since then, this tiny curious exhibit has adorned the Chicago Museum of Science and Industry. This rarity - a testament to the art of "alchemists" in the atomic era - could be admired during the Geneva conference in August 1955.

From the point of view of nuclear physics, several transformations of atoms into gold are possible. We will finally reveal the secret of the philosopher's stone and tell you how you can make gold. We emphasize here that the only possible way is the transformation of nuclei.

The stable gold, 197Au, could be obtained by radioactive decay of certain isotopes of neighboring elements. This is what the so-called nuclide map teaches us, in which all known isotopes and possible directions of their decay are presented. So gold-197 is formed from mercury-197 emitting beta rays, or from such mercury by K-capture. Gold could also be obtained from thallium-201 if this isotope emitted alpha rays. However, this is not observed. How to obtain an isotope of mercury with a mass number of 197, which is not found in nature? Theoretically, it can be obtained from thallium-197, and the latter from lead-197. Both nuclides spontaneously transform with electron capture into mercury-197 and thallium-197, respectively. In practice, this would be the only, albeit only theoretical, opportunity to make gold from lead. However, lead-197 is also only an artificial isotope, which must first be obtained by a nuclear reaction.

Isotopes of platinum 197Pt and mercury 197Hg are also obtained only by nuclear transformations. Only reactions based on natural isotopes are really feasible. Only 196 Hg, 198 Hg and 194 Pt are suitable starting materials for this. These isotopes could be bombarded with accelerated neutrons or alpha particles in order to arrive at the following reactions:

196 Hg + n = 197 Hg * + y

198 Hg + n = 197 Hg * + 2n

194 Pt + 4 He = 197 Hg * + n

With the same success, the desired isotope of platinum could be obtained from 194 Pt by the (n, y) -conversion or from 200 Hg by the (n, y) -process. In this case, of course, we must not forget that natural gold and platinum consist of a mixture of isotopes, so that in each case it is necessary to take into account the competing reactions. Pure gold will eventually have to be isolated from a mixture of various nuclides and unreacted isotopes. This process will be costly. The conversion of platinum into gold will have to be abandoned altogether for economic reasons: as you know, platinum is more expensive than gold.

Another option for the synthesis of gold is the direct nuclear transformation of natural isotopes, for example, according to the following equations:

200 Hg + p = 197 Au + 4 He

199 Hg + 2 D = 197 Au + 4 He

(Y, p) -process (mercury-198), (y, p) -process (platinum-194) or (p, y) or (D, n) -transformation (platinum-196 ). The only question is whether it is practically possible, and if so, is it cost-effective at all for the reasons mentioned. Only long-term bombardment of mercury with neutrons, which are present in the reactor in sufficient concentration, would be economical. Other particles would have to be produced or accelerated in a cyclotron - this method, as is known, gives only tiny yields of substances.

If natural mercury is exposed in a reactor to the action of a neutron flux, then, in addition to stable gold, mainly radioactive is formed. This radioactive gold (with mass numbers 198, 199 and 200) has a very short life span and within a few days it turns back into its original substances with the emission of beta radiation:

198 Hg + n = 198 Au * + p

198 Au = 198 Hg + e- (2.7 days)

It is not yet possible to exclude the reverse transformation of radioactive gold into mercury, that is, to break this "Circulus vitiosus": the laws of nature are not so easy to circumvent. The only stable isotope of gold is 197 Au 79, which guarantees its reliable and environmentally friendly production. The reason gold does not naturally convert to mercury is due to the accidental fact that the 197 Au nucleus is slightly more stable than the 197 Hg nucleus - by only 1 MeV. If, on the contrary, 197 Hg were more stable, then stable, natural gold would not exist at all. The fake gold bars would turn into a pool of mercury.

Under these conditions, synthetic production of an expensive noble metal - platinum, seems less complicated than alchemy. If it were possible to direct the neutron bombardment in the reactor so that predominantly (n, y) -transformation occurred, then one could hope to obtain significant amounts of platinum from mercury: all common isotopes of mercury - 198 Hg, 199 Hg, 201 Hg - are converted into stable isotopes of platinum - 195 Pt, 196 Pt and 198 Pt. Of course, here, too, the process of separating synthetic platinum is very complicated.

Frederick Soddy, back in 1913, proposed a way to obtain gold by nuclear transformation of thallium, mercury or lead. However, at that time, scientists did not know anything about the isotopic composition of these elements. If the process of elimination of alpha and beta particles proposed by Soddy could be carried out, one would have to proceed from the isotopes 201 Tl, 201 Hg, 205 Pb. Of these, only the 201 Hg isotope exists in nature, mixed with other isotopes of this element and chemically inseparable. Consequently, Soddy's recipe was not feasible.

The writer Dauman, in his book "THE END OF GOLD", published in 1938, gave us a recipe for turning bismuth into gold: by splitting off two alpha particles from the bismuth nucleus using high-energy X-rays. Such a (y, 2a) -reaction is not known to date. In addition, the hypothetical transformation 205 Bi + y = 197 Au + 2a cannot proceed for another reason: there is no stable isotope 205 Bi. Bismuth is a monoisotopic element! The only natural isotope of bismuth with a mass number of 209 can give according to the principle of the Dauman reaction - only radioactive gold-201, which with a half-life of 26 minutes again turns into mercury. As you can see, the hero of Dauman's novel, the scientist Bargengrond, could not get gold!

We now know how to actually get gold. Armed with the knowledge of nuclear physics, let's venture on a thought experiment: 50 kg. we will turn mercury in an atomic reactor into full-fledged gold - into gold-197. Real gold is made from mercury-196. Unfortunately, mercury contains only 0.148% of this isotope. Therefore, at 50 kg. there is only 74 g of mercury-196, and only this amount can we transmute into true gold.

In the beginning, let us be optimistic and assume that these 74 g of mercury-196 can be converted into the same amount of gold-197 if the mercury is bombarded with neutrons in a modern reactor with a capacity of 10 15 neutrons / (cm 2 s). Let's imagine 50 kg. mercury, that is, 3.7 liters, in the form of a ball placed in a reactor, then a stream of 1.16 will act on the surface of mercury equal to 1157 cm 2 every second. 10 18 neutrons. Of these, 74 g of isotope-196 are affected by 0.148%, or 1.69. 10 15 neutrons. For simplicity, let us further assume that each neutron causes the transformation of 196 Hg into 197 Hg *, from which 197 Au is formed by electron capture.

Therefore, we have 1.69 at our disposal. 10 15 neutrons per second in order to transform atoms of mercury-196. How many atoms are they actually? One mole of the element, that is, 197 g of gold, 238 g of uranium, 4 g of helium, contains 6.022. 10 23 atoms. We can get an approximate idea of this gigantic number only on the basis of visual comparison. For example, this: let's imagine that the entire population of the globe in 1990 - about 6 billion people - started counting this number of atoms. Each one counts one atom per second. In the first second, they would have counted 6. 10 9 atoms, in two seconds - 12. 10 9 atoms, etc. How long will it take for humanity in 1990 to count all the atoms in one mole? The answer is staggering: about 3,200,000 years!

74 g of mercury-196 contains 2.27. 10 23 atoms. We can transmute 1.69 per second with a given neutron flux. 10 15 mercury atoms. How long does it take to convert all of the mercury-196? Here's the answer: It will take an intense neutron bombardment from a high flux reactor for four and a half years! We have to make these huge expenses in order to get only 74 g of gold out of 50 kg of mercury in the end, and such synthetic gold must still be separated from the radioactive isotopes of gold, mercury, etc.

Yes, it is, in the age of the atom you can make gold. However, the process is too expensive. The gold obtained artificially in the reactor is priceless. It would be easier to sell a mixture of its radioactive isotopes as “gold”. Maybe science fiction writers will be seduced by inventions involving this “cheap” (in quotes) gold?

"Mare tingerem, si mercuris esset" (I would turn the sea into gold if it consisted of mercury). This saying was attributed to the alchemist Raimundus Lullus. Suppose that we, with the help of modern science, turned not the sea, but a large amount of mercury into 100 kg. gold in a nuclear reactor. Outwardly indistinguishable from natural, this radioactive gold lies in front of us in the form of shiny ingots. From the point of view of chemistry, this is also pure gold.

Some very wealthy person buys these bars at what is believed to be a similar price. He does not even suspect that in reality we are talking about a mixture of radioactive isotopes 198 Au and 199 Au, the half-life of which is from 65 to 75 hours. You can imagine this curmudgeon who saw that his golden treasure is literally slipping through his fingers.

For every three days, his property is reduced by half, and he is unable to prevent it; in a week from 100 kg. only 20 kg of gold will remain, after ten half-lives (30 days) - practically nothing (theoretically it is another 80 g). Only a large pool of mercury will remain in the treasury.

Plutonium is the first man-made element seen by the human eye
"Hell" and "madness"
Gold obtained in an atomic reactor
The secret of the gold medallion

Radioactive gold is more valuable than natural gold

In discussing the possibility of artificially producing gold from mercury, we saw that the reverse conversion of gold to mercury is not so impossible. In essence, it is only through a whim of nature that gold exists as a natural element. The reason that gold does not naturally convert into mercury lies in the slightly higher stability of the 197 Au nucleus compared to 197 Hg - by only 1 MeV. If, on the contrary, 197 Hg were more stable, then natural gold would not exist at all. The fake gold bars would turn into a pool of mercury.

The news that they tried to convert gold for scientific purposes into another element, for example, into mercury, would certainly have led to bewilderment of the secret adherents of alchemy. What are the reasons for this "inverted alchemy"?

At one time, the isotope of mercury with a mass number of 198 acquired special importance in measuring technology. This isotope was required in a very pure form. Either it was not possible to isolate it from natural mercury, or it was impossible because of the enormous costs. There was only one way to go. It was necessary to obtain mercury-198 artificially, and this required gold. Why, for science, light converges like a wedge on this mercury?

A meter is one forty-millionth part of the Earth's equatorial circumference. This is how they used to be taught at school.
Since 1889, the standard of the meter has been kept in Paris - a rod made of an alloy of platinum with iridium. However, this benchmark is an artificial measure that can change.
Looking for constant, natural standard of length soon found another unit: one meter corresponds to 1553164.1 wavelengths of the red spectral line of cadmium, equal to 6438 angstroms (1 Â = 10 -10 m). With the help of such a standard, a fairly high accuracy has been achieved, sufficient for many purposes. During World War II, British air and sea navigation instrument designers used only cadmium red line values for secrecy purposes.

However, the new measure of length still did not meet the highest requirements. Cadmium is a mixed element, and each of its isotopes gives a red spectral line, the wavelength of which is slightly different from the others. Therefore, back in 1940, American physicists Vines and Alvarez suggested assigning to the green line of the spectrum of mercury-198 with a wavelength of 5461 A. This line is sharply limited and absolutely monochromatic. Vines and Alvarez by bombarding gold with neutrons in a cyclotron for a month obtained mercury-198 in quantities necessary for spectral analysis.

The resulting isotope of mercury was separated by incandescence. Its vapors condensed in tiny capillaries.

After World War II, the first Mercury-198 Lamps went on sale in the United States. They contained 1 mg of mercury-198, which was obtained from gold in an atomic reactor. Other states soon began releasing the required isotope of mercury as well. Since 1966, it has been received in the GDR, at the Central Institute for Nuclear Research in Rossendorf. In the local nuclear reactor, chemists obtained about 100 mg of mercury-198 with an isotopic purity of 99% from 95 g of pure gold as a result of its 1000-hour neutron bombardment:

197 Au + n= 198 Au * + γ
198 Au * = 198 Hg + e -

On the basis of this new standard for length, the meter was "re-measured" again. It is 1,831,249.21 wavelengths of the green line of the 198 Hg isotope. At present, mercury-198 is again replaced by the isotope of the noble gas krypton - 86 Kr, the orange line of which is 6058 A in length is more reproducible.

One meter corresponds to 1,650,763.73 wavelengths of radiation from krypton-86 atoms in a vacuum.

The intermediate product of the synthesis of mercury-198 - radioactive gold-198 - has also found application. This isotope emits beta rays and decays with a half-life of 65 hours to the stable isotope 198 Hg. At present, it is used as a medicine - in a finely dispersed state in the form of a golden sol. It is used to obtain radiograms of organs of the human body and to treat cancerous tumors. For this purpose, it is injected into the respective tissues. Each gold atom acts like a small X-ray tube and kills cancer cells in a highly restricted area.

Such therapy is much more expedient than irradiation of large surfaces. Radioactive gold is significantly less harmful than X-rays. Cases of healing in the treatment of leukemias, a painful increase in the number of white blood corpuscles, are also very illustrative. In the fight against the scourge of cancer, artificial radioactive gold has already provided invaluable services to mankind.

Modern science will say beyond any doubt: transformation of elements - yes, transformation into gold - no! For what? Today, gold is wasted without hesitation to synthesize other elements of interest to science. Gold is used to artificially obtain isotopes of france and astatine, elements that, as you know, cannot be obtained from natural sources. Here, too, alchemy is turned upside down. Francium is obtained from gold, which is bombarded with oxygen or neon ions in modern accelerators:

197 Au + 22 Ne = 212 Fr + 4 He + 3 n

Astatine is formed by converting gold when it is bombarded with overclocked carbon nuclei:

197 Au + 12 С = 205 At + 4 n

This is how "expensive" gold has become for modern science: it does not seek to obtain it artificially, but rather uses it as a "raw material" for the synthesis of other elements.

Gold has long established itself as an element of the global financial system. The reserves of this metal are small, which is why, over the course of history, gold was practically not lost, no matter what cataclysms the human society had to endure: the yellow metal was melted and accumulated. Products made of gold and ingots today act as the most important objects for investment of funds. The use of gold is not limited to investment. The metal is used in the production of jewelry, in the implementation of modern technologies in various industries, as well as in medicine.

Industrial value of gold

The value of the yellow metal for industrial production is due to its special properties: malleability and ductility. Thanks to these qualities, a micron wire or an ultra-thin sheet of foil can be made from raw materials.

Gold is characterized by a high degree of resistance to aggressive environments. This property allows the metal to be used in the chemical industry and electronics, even despite the lower thermal and electrical conductivity compared to the same copper.

The use of gold in modern industry is most often found in:

Transport industry;
Chemistry and petrochemical production;
Energy;
Electronics and measuring instruments manufacturing;
Telecommunications;
Nanotechnology;
Aviation and space industry.

Metal has become widespread as a welding material in the production of the latest technology samples, the production of thermocouples, and parts for galvanometers. In terms of its chemical and mechanical resistance, gold lags behind most of the platinoids, but it is irreplaceable as a raw material for electrical contacts. In the field of microelectronics, both gold conductors and galvanic gold plating of individual surfaces, boards and connectors are widely used.

Where else is gold used in industry? Metal is used as a solder when soldering metals, as it wets working surfaces well. Gold is also irreplaceable in the defense industry: targets for nuclear research are made of it, used as a coating for mirrors designed to operate in the far infrared range, and used for a neutron bomb shell. Electroplating of metals eliminates corrosion processes, and thin plates made of soft gold alloys are important in the field of ultrahigh vacuum research.

Due to the ability of gold to reflect infrared rays, man has found another use for the metal: the glass industry. The metallization of building windows is made up of an insert of a thin gold film. Such measures allow to ensure that most of the rays are reflected and to avoid heating the building. If an electric current is passed through such glass, it will acquire anti-fog properties, which are indispensable for the manufacture of glasses for large vehicles - airplanes, electric locomotives, sea vessels.

The use of gold in the aviation and space industries may seem somewhat strange, because the weight of the metal is quite large. Gold is used where corrosion cannot be prevented in any way: this is the connection of parts of aircraft engines, and the places where electrical contacts are soldered, and the covering of shuttle windows with gold film.

Jewelery industry

Jewelry production has always been and remains the largest consumer of yellow metal. Gold jewelry has existed for many centuries, at least one can recall the ancient Egyptian pharaohs and the decoration of their tombs. Wearing gold items used to have a slightly different meaning: they were amulets against diseases, attacks, witchcraft. In the modern world, jewelry made of yellow metal embodies the status of their owner in society, and also carries aesthetic beauty.

The fashion for this metal is unlikely to pass over time, so the question of where gold is still used by a person can be safely answered - in jewelry. The assortment of gold jewelry is quite extensive; rings, earrings, chains, cufflinks, fingers and other products are made of metal. Jewelers make their masterpieces not from pure gold, but from its alloys. This is explained by the fact that pure metal is very soft and does not have the necessary strength in relation to mechanical stress.

In order to achieve the desired characteristics, in production, they first make an alloy of the metal with other additives, the main of which are silver and copper. Other components of the alloy include palladium, zinc, cobalt and nickel. The ratio of the components determines the fineness of the alloy. Gold provides resistance to corrosion processes, but the mechanical properties of the alloy and its color shade depend on the content of other metals. Depending on the ratio of metals in the alloy, gold jewelry has one of the shades of a three-color palette: yellow, white and red gold are distinguished.

Ring made of "red" gold.

The use of gold in jewelry dyeing accounts for about half of the total amount of metal that is used by humans.

Another significant item of expenditure of precious metal reserves - about 10% - is medicine.

Gold in medicine

Due to its good malleability and ability not to oxidize, gold has been widely used in dentistry since ancient times. For dentures and crowns, it takes, as well as for jewelry, not pure gold, but its alloys. All the same silver, copper, zinc, platinum are used as additional components. The result is a product with good ductility, excellent corrosion resistance and high mechanical properties - all that is required for dental prosthetics.

Where else is gold used for medicinal purposes? Pharmacology remains one of the most important areas of precious metal use. Metal compounds are a component of some drugs that are used in the treatment of arthritis, malignant tumors, and tuberculosis. Examples of the use of gold in medicine include water-soluble preparations containing precious metals, which are administered as injections to a patient with chronic arthritis, gold thiosulfate administered to patients with erythematous lupus, organic metal compounds used in tuberculosis.

Radioactive gold, used in oncology for the diagnosis and treatment of malignant tumors, gold threads in aesthetic cosmetology, gold-containing skin care preparations, which, thanks to the antimicrobial effect of metal, help to eliminate skin problems and rejuvenate them.

The advances in science that have presented gold-containing preparations to mankind have made it possible to achieve great results in the treatment of many diseases, especially in oncology, where radioactive gold is used, or rather the colloidal particles of its isotopes. In addition, it helps to cope with some ailments and simply wearing gold jewelry. The thesis about the beneficial effects of gold on the human body is actively used in alternative medicine recipes:

Improves memory, prevents the development of atherosclerosis;
Strengthens the heart and the entire circulatory system;
Helps to cope with colds;
Adds vivacity and energy.

The beneficial properties of gold may not always be beneficial to a particular person. Before being treated with gold, it is recommended to consult a doctor. Even the simple wearing of precious metal products can cause a negative reaction in the body: fever, pain in the intestines, kidney problems, hair loss and even depression. Such phenomena do occur in some people who have been in constant contact with gold.

The use of gold as an industrial and medicinal metal in the life of people is quite extensive. Fields of application include spacecraft engines, gold rings on the fingers of modern women of fashion, and dentures in the dentist's office. Gold as a precious metal has retained its investment, industrial, jewelry and medical purposes for several millennia. This trend is unlikely to be interrupted in the future, the properties of the yellow metal will always be used by scientists, expanding the boundaries of its modern application.

198 Au is used in the form of colloidal solutions for radioisotope diagnostics and in radiation therapy.

1. Small medical encyclopedia. - M .: Medical encyclopedia. 1991-96 2. First aid. - M .: Great Russian Encyclopedia. 1994 3. Encyclopedic Dictionary of Medical Terms. - M .: Soviet encyclopedia. - 1982-1984.

See what "radioactive gold" is in other dictionaries:

A group of radioactive isotopes of gold with mass numbers ranging from 187 to 203 and a half-life of 2 seconds. up to 31,016 years old; 198Au isotope is used in the form of colloidal solutions for radioisotope diagnostics and in radiation therapy ... Comprehensive Medical Dictionary

Au (lat.Aurum * a. Gold; n. Gold; f. Or; and. Oro), chem. element of group I periodic. Mendeleev systems; at. n. 79, at. m. 196.967. Natural gold consists of the stable isotope 197Au. 13 radioactive isotopes with mass numbers ... ... Geological encyclopedia

This term has other meanings, see Gold (disambiguation). 79 Platinum ← Gold → Mercury ... Wikipedia

- (lat. Aurum) Au, chemical element of group 1 of the periodic system of Mendeleev; atomic number 79, atomic mass 196.9665; heavy yellow metal. Consists of one stable isotope 197Au. Historical reference. Z. was ... ...

Gold, silver, platinum and platinum group metals (iridium, osmium, palladium, rhodium, ruthenium), which got their name mainly due to the high chemical resistance and beautiful appearance in the products. In addition, Gold, ... ... Great Soviet Encyclopedia

Precious metals- (Precious metals) Precious metals are rare metals that are distinguished by their brilliance, beauty and corrosion resistance History of the extraction of precious metals, varieties, properties, applications, distribution in nature, alloys ... ... Investor encyclopedia

Gold / Aurum (Au) Atomic number 79 Appearance of a simple substance Soft malleable yellow metal Properties of the atom Atomic mass (molar mass) 196.96654 a. units (g / mol) Radius of an atom ... Wikipedia

Precious metals Metals that are not subject to corrosion and oxidation, which distinguishes them from most base metals. All of them are also precious metals due to their rarity. The main precious metals are gold, silver, and also ... ... Wikipedia

Gold is a yellow very dangerous and poisonous metal
modern precision digital and cable technologies
Toxic and poisonous stones and minerals

Gold(Au). Since the earliest times gold was known to the peoples of our planet. There is a version that gold was practically the first metal that a person first met (after pyrite - iron pyrite, "gold blende"). There is evidence that in Egypt, at the ancient gold mines of the Jews ("Ibriim" - "aliens"), gold was mined and used in the manufacture of various products in the IV millennium BC, and in Indochina and India - in the second millennium BC. There, gold served as a material for the manufacture of coins, jewelry, art and cult items.

Before the introduction of electronic money, gold was an element of the financial system, this metal was not subject to corrosion (with the exception of mercury amalgam, imitation of lead, galvanizing of silver, and other scams of the 20th century), has an attractive appearance, and its reserves are large (especially in seawater - "the curse" of the modern glass industry, quartz with impurities of gold is melted in a crucible with red cinnabar - mercury sulfide and gold is slagged out of quartz for the needs of electroplating).

Even in antiquity, gold was used as a material for making money (thieves imbued with amalgam of mercury on the outskirts of Almaden, Spain, west of continental Europe, "money silver"). Until now, gold coins remain a monument of antiquity. The period from 1817 to 1914 is even called the "golden age". Until the end of the First World War, gold continued to be the measure of the coins of money existing at that time (until the beginning of the 21st century). Paper notes at that time served as documents certifying the ownership of a part of the gold, banknotes were exchanged for gold (fraud - pyrite, iron sulfide, "fool's gold", in combination with "fools' silver" - arsenous iron sulfide arsenopyrite, Gold rush in Alaska, USA).

In accordance with wrong tradition (abolished under Peter I in Russia), the purity of gold is rarely measured in non-metric carats... One such carat is equal to one twenty-fourth part of a gold alloy (alchemy is amalgam, an alloy of gold with mercury in order to deceive the customs and present the gold alloy as silver with subsequent evaporation of mercury, illegal "jewelry business" of Armenians of the late 19th - early 20th centuries).

Gold with the mark "24K" is supposedly absolutely pure, i.e. has absolutely no impurities (the war of the Scarlet and White Rose between Britain and France, without Spain - gold amalgam). Gold impurities are created for various purposes, primarily to deceive consumers, therefore, the non-metric gold system is prohibited in Ukraine. If the alloy will have a non-metric (" British") mark" 18K ", this will mean that this alloy allegedly contains 18 parts of gold and 6 parts of various impurities (" special "or" Armenian "" gold ").

In the CIS countries, the metric (Spanish, the so-called " ton") measurement system. The purity of gold is measured by the so-called breakdown ( thousandths). The sample value ranges from zero to one thousand, the sample value shows the gold content in the alloy in thousandths. For example, the above described fake "grade" "18K" can be recalculated, as a result of which we get the 750th sample, "24K", i.e. pure jewelry gold, corresponds to the 996th standard and is considered "practically pure", it is used in the manufacture of jewelry. Gold of a higher purity is rare, its production requires costs, such gold is used in chemistry, computer technology and precision electronics.

Gold is a soft metal with a yellow color (similar to pyrite - iron sulfide). Impurities of other metals give a reddish tint to gold alloys, for example, coins and jewelry, in particular, there is often an impurity of copper (the "Armenian scam" in Spain in the Middle Ages, under Ivan the Terrible was the cause of mass executions and riots in Russia, the so-called . the fight against "amalgam jids") - imitate the presence of the red cinnabar of Spain (Almaden, Western Continental Europe) in the manufacture of gold amalgam "for silver".

When making thin (like paper) gold leaf - micron gold films, the metal begins to shine green (like the sea). Gold, as a metal, has a high thermal conductivity, while at the same time having a low electrical resistance (it is actively attacked by computer manufacturers).

Gold crystals from California. Photo: V. Levitsky.

Biological properties

The mechanism of the biological effect of gold is being investigated, recently it has become known that gold is a part of metalloproteids, interacts with copper and proteases, which hydrolyze collagen, as well as with elastases and other active components of connective tissues. Gold is involved in the processes of binding hormones in tissues.

The trace element gold can enhance the bactericidal effect of silver. It has an antiseptic effect on viruses and bacteria. Sometimes gold may participate in improving the body's immune processes.

The human body contains about 10 mg of gold, about half of this amount is in the bones (germinal centers of growth of calcium crystals, it is worn by young people). The distribution of gold throughout the body depends on the solubility of metal compounds (in the zones of bone growth, etc.). Colloidal gold compounds accumulate in the liver, and soluble ones - in the kidneys.

Nothing concrete is known about the biological role of gold, about the daily requirement of the metal. Gold is present in the grains, stalks and leaves of corn ("maize" is grown and eaten). The water of the oceans contains a gigantic amount of gold (from ~ 0 to 65 mg / t) and is noticeably green in the thickness. Lethal and toxic doses for humans have not been determined (often, gold is taken with seawater during a storm, tsunami and illiteracy).

Metallic gold is toxic, and organic derivatives used as pharmaceuticals are active. Certain organic gold compounds can accumulate in the liver, kidneys, hypothalamus, and spleen, which can lead to dermatitis and organic diseases, thrombocytopenia and stomatitis.

Determination of the gold content in the body is carried out on the basis of the study of biosubstrates (biopsies and blood). With gold poisoning, the content of coproporphyrin in the urine increases. Gold is a potentially toxic element.

Metallic gold is not absorbed, while gold salts can have a high toxic effect, which is similar to that of mercury (imitation of the so-called "Spanish flu" - a disease when working with mercury and cinnabar).

Despite the fact that gold is a relatively inert metal, people with gold jewelry can develop contact dermatitis. In some cases, gold causes sensitization of the body, this is confirmed in dental practice, plastic surgery and a number of other cases (zirconium is used).

Gold poisoning. The negative effect of excess gold is removed by the introduction of 2,3-dimercaptopropranol, in which the SH group strips off gold from SH-containing proteins and restores their normal properties (but there is an intolerance to this treatment and hormones, in this case they give red medical cinnabar) ...

Excessive gold manifestations: drooling, metallic taste in the mouth; vomiting, spasms, excretion of protein in the urine; the appearance of painful spots on the skin; pain along the nerves (neuritis); pancytopenia (leukopenia, thrombocytopenia); state of arousal; skin rashes. diarrhea; symptoms of depression of the central nervous system; increased sweating; colic and pain in the intestines, pain in bones, joints, muscles; swelling of the legs (accompanies uranium poisoning); weight loss, aplastic bone marrow hypoplasia; conjunctivitis; itching, skin inflammation, fever, malaise; bone and joint pain; generalized eczema; inflammation of the mucous membranes of the tongue and mouth; throat pain, aplastic anemia; nephrotic syndrome, glomerulonephritis; vomiting, diarrhea.

Chemical elements that are antagonists and synergists of gold have been identified - mercury and cinnabar. As auxiliary drugs, it is possible to use antithymocyte globulin, androgens, corticosteroids. In some cases, the use of hematopoietic stimulants, bone marrow transplantation is indicated.

In the middle of the 20th century, gold was used in the treatment of tuberculosis, leprosy, syphilis, epilepsy, eye diseases, and malignant tumors in Spain (instead of cinnabar). Today, preparations based on gold salts are used in the treatment of rheumatoid and psoriatic arthritis, Felty's syndrome, and lupus erythematosus. These include chrysanol, auranofin, and others (with hormone tolerance).

Interesting Facts

During the reign of Pharaoh Thutmose III, gold was stolen at the VAK especially actively (from chemists). The content of gold on the surface of the Sun is an order of magnitude higher than in the earth's crust.

By the end of the XIX century. in the Irkutsk region of the Russian Federation, a nugget weighing 22.6 kg was found. Large for large nuggets was found in the Urals. The largest nugget - "Big Triangle" with dimensions 39 × 33 × 25.4 cm and a mass of 36.157 kg was found in the South Urals in 1842. The largest nugget in the world, the Halterman Plate, was 140 × 66 × 10 cm in size and weighs 285.76 kg and consisted of gold and quartz. 93.3 kg of gold was smelted from it.

At one exhibition, a small, polished golden cube was shown, the size of which is slightly more than 5 cm, and the announcement said that the person who can lift the cube with two fingers of his hand will be able to take it with him.

If a room with an area of 20 square meters and a height of 2.85 m is filled with gold bars, the mass of gold will be 1150 tons, which is equal to the weight of a loaded train (meaning a working train in Almaden, Spain, western Europe - leaving the mine with cinnabar).

In the synthesis of Mendelevium atoms, gold foil was used as a target, and a negligible amount (only 1,000,000,000 atoms) of Einsteinium was electrochemically applied to it. Such gold substrates for nuclear targets have sometimes been used in the synthesis of other elements.

Gold nuggets are never gold. They usually contain a lot of copper or silver. Native gold contains tellurium (a catalyst for the growth of crystals and gold nuggets, especially in calderas).

In the lane. floor. XIX century. the merchant Shelkovnikov went from Irkutsk to Yakutsk. At the Krestovaya parking lot, he learned: the Evenks (Tungus), who hunt birds and animals, buy gunpowder in the trading post, and pigs (in the Donetsk region of Ukraine) "get" themselves red paint for monasteries of the Russian Federation fled from the city of Almaden, Spain, western Europe - they did not reach the southeast of Donetsk region.Ukraine, Nikitovka, Gorlovka, the deposit of cinnabar druses and crystals similar to the physalis plant, they ran into military patrols).

It turned out that a bunch of "soft yellow stones" could be collected along the Tonguda river bed, they could be easily "rounded" - most likely we are talking about pyrite ("fools' gold"). Soon, gold mines were organized in the upper reaches of the river (pyrite is a satellite of gold, a sign of a caldera).

In the end. XIIIV century chemists managed to extract colloidal solutions of gold. But these solutions were purple in color. And in 1905, under the influence of alcohol on weak solutions of gold chloride, colloidal gold solutions of red and blue colors were obtained. The color of such a solution is closely related to the size of the colloidal particles.

Ernst Werner Siemens, when he was young, fought in a duel, later he was imprisoned for this. The scientist managed to obtain permission from the administration to organize a laboratory in the cell and in prison he continued experiments on electroplating. He developed a method of gilding base metals (electroplating is a strong point of the Russian Federation, Ukraine does not have this).

When the task was close to being solved, a pardon came. Instead of the joy of freedom, the prisoner gave a request to leave him in prison for a while and finish the experiments. But the authorities threw the inventor out of jail. He had to re-equip the laboratory and finish what he started in prison at home. Siemens nevertheless filed a patent for the gilding method (with amalgam), but this happened later than the inventor would have liked (he believed that mercury was liquid).

History

Ancient gold mines were located in Egypt. There is evidence of the manufacture of gold items in the 5th millennium BC, i.e. during the Stone Age. In ancient times, the Egyptians mined gold in the Arabian-Nubian province, which is located between the Red Sea and the Nile. During the reign of about 30 dynasties, this gold mine produced about 3.5 thousand tons of gold (gold mines of the Jews).

By the time of the capture by Rome, the Egyptians had managed to steal about 6 thousand tons of gold from the Jews. Countless riches have been plundered almost entirely.

In antiquity, the gold-bearing rocks of Spain brought about 1.5 thousand tons of gold to the Romans. The mines of Austria-Hungary in the Middle Ages produced 6.5 tons annually. On the coins of that time one can find inscriptions in Latin "from the gold of the Danube" or "from the gold of the Rhine", etc. In Scandinavia, little gold was mined, only a few kilograms annually. Columbus's voyage made it possible to discover Colombia, which for many years had the largest gold and pyrite mining in the world. In Brazil, Australia and other countries in the XVIII - XIX centuries. found quite rich gold-bearing placers.

For a long time there was no gold mining in Russia. Scientists differ on the first Russian production. Apparently, the first gold was mined from the Nerchinsk ores of the Russian Federation in 1704 (Peter I), where it was together with silver. Silver with a gold content was smelted at the Moscow Mint. This method was laborious and time-consuming, for more than 50 years less than 1 ton of gold has been extracted by this method. There is a rumor that the thieves Demidovs in 1745 secretly smelted 6 kg of gold in the Altai mines (they stole the gold). In 1746, the gold mines became the property of the family of Peter I.

In the Urals, in 1745, an ore gold mine was opened. This made it possible to start industrial mining of crystalline metal (crystalline shield of gold).

Economic waves of instability in the United States (non-delivery of red cinnabar from Almaden, Spain, for the needs of industry and production) forced the price of gold to increase. In 1976, a decision came into force to remove the pegging of currencies to gold and to establish floating rates (cinnabar). Thus, gold ceased to be a currency, and the dollar ceased to be a reserve currency (this is the usual US currency, the US government).

As a result of all these changes, gold has ceased to be an investment object. Gold price changed in 96-99. XX century in connection with the beginning of sabotage and work stoppage at the mines of red cinnabar, which is used to extract gold, in the city of Almadena, Spain (bankruptcy of production in 2004).

Being in nature

Except for gold, the earth contains little, about 4.3 · 10 -7% by weight. On average, a ton of rocks contains 4 milligrams of gold. Gold is one of the rare metals on earth (the hard part of the lithosphere). If we assume that earthly gold would be dispersed evenly over the planet, as in seawater (where there is a lot of it), then the extraction of the metal would become impossible. But gold tends to migrate, for example, with underground waters to the hot batholiths of volcanoes and settle in the sources of mountain and other rivers, with dissolved oxygen. As a result of such migration processes, the gold content in some places increases sharply: quartz gold-bearing veins are literally impregnated with it, and gold-bearing sand appears.

Gold can be ore and loose. Ore gold has the form of small gold grains (0.0001 - 1 mm) embedded in quartz. In this form, the metal is found in quartz rocks in the form of thin inclusions, sometimes in the form of powerful veins that permeate sulfide ores - copper pyrite CuFeS 2, sulfur pyrite FeS 2, antimony luster Sb 2 S 3 and others. Another form of natural gold is its rare minerals, in which gold is in the form of chemical compounds (most often - with tellurium, with which gold forms silvery-white crystals, less often they have a yellow tint): montbreyite Au 2 Te 3, calaverite AuTe 2, mutmannite (Ag, Au) Te (the parentheses show that these elements can be present in the mineral in different proportions), sylvanite (Ag, Au) 2 Te 4, krennerite (Ag, Au) Te 2, montbreyite (Au , Sb) 2 Te 3, aurostibite AuSb 2, petzite Ag 3 AuTe 2, auricupride Cu 3 Au, aurantimonate AuSbO 3, fishesserite Ag 3 AuSe 2, tetraauricupride AuCu, nagiagite Pb 5 Au (Te, Sb) 4S 5–8 and others ...

Sometimes gold can be present as impurities in various sulfide minerals, such as pyrite, chalcopyrite, sphalerite and others. The most modern methods of chemical analysis make it possible to detect the presence of even trace amounts of "aurum" in the organisms of animals and plants, in cognacs and wines, in sea water and mineral waters.

In the process of geological changes, some of the gold was removed from the location of the primary deposition and re-deposited in other places of secondary occurrence, as a result of which the so-called placer gold was formed, which is a product of the process of destruction of fundamental deposits that accumulate in river valleys. There are rarely cases of finds of rather large gold nuggets, which have a bizarre shape. Some of these deposits were formed around 20-30 thousand years BC.

Native gold is not chemically pure. It always, without exception, contains impurities, often in decent quantities. Silver impurities can be from 2% to 50%, copper impurities usually make up up to 20% of the mixture, the nugget can contain iron, lead, mercury, bismuth, tellurium, platinum group metals and others. A natural alloy of gold and silver, in which about 15-20% silver and an insignificant admixture of copper, in ancient Greece was called an electron (the Romans sounded like "electrum") - an imitation of amber, does not electrify when rubbed against wool. This was due to the yellow color, in Greek the word "elektor" means the sun, the sun, from where the Greek "elektron" came from, i.e. amber.

Application

Currently, the gold available in the world is distributed approximately like this: 10% - in industry, 45% - from individuals (bullion and jewelry) and 45% - centralized reserves (standard bars of chemically pure gold).

In 2005, swindler Rick Munarritz asked a hypothetical question: where is it more profitable to invest - in gold (in the form of someone else's iron sulfide - "fool's gold") or in the Google search engine? The answer is simple - in Google, there is more real (technical galvanic) gold (gilding of "legs" of modern 32-bit PC processors by electroplating in the Russian Federation, gilding of contacts of coaxial cables, including acoustic computer digital processor audio systems, cable Internet, main faraim and other modern computer technologies).

Gold is an integral element of the global computer system, because this metal does not corrode, has many areas of technical application, and its use is limited. Gold was actively lost during historical cataclysms, melted, polluted and accumulated. The result was the bankruptcy of the 20th century. on gold (before the introduction of modern computer technologies). Au returnes ...

In terms of mechanical strength and chemical resistance, gold is inferior to platinoids, but it is irreplaceable as a running material for the manufacture of electrical contacts. That is why electroplating coatings with gold plating of connectors, contact surfaces, printed circuit boards, as well as gold conductors are used very widely in microelectronics.

Gold is used as a target in nuclear research, as a coating for mirrors that operate in the far infrared, as a special shell in a neutron (hydrogen) bomb.

Amalgamated solders made of mercury and gold wet various metal surfaces and are used for soldering metals (pink-red powder additive to gold - red cinnabar). Thin gaskets made of soft gold alloys are used in the ultra-high vacuum technique.

Metal gilding is used for corrosion protection. Although such a coating of metals has disadvantages, it is also common because the finished product becomes more expensive in appearance, "galvanized". Gold was registered as food additive E175.

Significant quantities of gold were consumed by dentistry: alloys of gold and silver, copper, nickel, platinum, zinc are used to make dentures and crowns. It gave way to modern zirconium, platinum, iridium and other alloys because of the predatory hunt for gold in cemeteries - it was stolen and melted into uncontrolled stolen jewelry and went bankrupt in 1989-1985. jewelry industry (gold amalgam, globally).

The composition of medicines includes gold compounds (amalgam and a mixture with red cinnabar). They are used in the treatment of rheumatoid arthritis, tuberculosis, etc. Radioactive gold is used in the treatment (diagnosis and search) of many malignant tumors.

Production

At the moment, South Africa is a major supplier of the world gold market, where mines have reached a depth of 4 km. The Waal Reefs mine in South Africa is the largest in the world. In South Africa, gold production is the country's main production (instead of uranium ...).

Due to the concentration of gold in nature, a tenth is theoretically available for mining. Gold crystal mining began with nuggets that shine brightly and are visible. But there are few such nuggets, so the most important way was to wash the sand.

Gold is about 8 times heavier than sand and 20 times heavier than water, so you can wash the gold out of the sand with a jet of water. The oldest method of washing out is reflected in the ancient Greek myth of the golden fleece, i.e. grains of gold after washing out were deposited on the lamb skin. Placers of gold used to be quite common in rivers that have eaten away gold-bearing rocks for centuries.

Today, the extraction of gold from ore has become mechanized, but despite this, the process remains complex and hides deep underground. Recently, they began to proceed from economic efficiency when searching for deposits. It is substantiated that if the content is 2-3 g of gold in 1 ton of ore, and if the content is 10 g or more, it is already considered rich. Among all the costs. used for geological exploration, the cost of prospecting for gold ores is from 50 to 80%.

There is a mercury method for extracting gold from ore. It is based on the fact that mercury wets gold and dissolves it. The crushed gold-bearing ore was shaken in barrels, and at the bottom there was mercury or cinnabar (in the latter case, the barrel was heated, for which the swindlers stole coal). Gold particles adhered to the released mercury and formed a chemical amalgam of gold (theft of alchemists in Almaden, Spain).

Because the color of the gold particles disappears, it seems that the gold has "dissolved" - turned into "silver" or "platinum" ("silver", poison - this is how Tsar Alexei Mikhailovich Romanov was deceived, mid-17th century, Russia). Then the gold amalgam mixture was heated (with sulfur and coal, the furnace was closed). Volatile mercury partially disappeared (poison for women is an aphrodisiac), gold remained. Disadvantages: mercury is highly toxic, incomplete gold release (cracks, mercury remains).

There is also a modern method - leaching with sodium cyanide, when small grains are converted into water-soluble compounds (uranium extraction technology, for example). Gold is extracted from an aqueous solution, for example, it is extracted using zinc powder: 2Na + Zn = Na + 2Au.

The process allows you to extract gold from mining dumps, turning them into a new deposit. There is also a method of underground leaching, in which a cyanide solution is pumped into the wells, through cracks it penetrates into the rock and dissolves gold, and then the solution is pumped out from other wells. Cyanide will dissolve with gold, and other metals that form cyanide complexes.

Another constant source of gold mining is intermediate products of copper, uranium, lead-zinc and other industries. Gold is adjacent to other metals. When refining copper, after dissolution of the anode, precious metals accumulate under the anode in the sludge. This sludge is an important source of gold, which is mined the more, the larger the production of base metals.

Recycled gold is obtained from defective or used electronics products. Scrap gold is an important source of recycled gold.

Along with small grains, large nuggets are also found, which are written about in newspapers and talked about on radio and TV. Most of the large nuggets were found in the Urals (RF).

Physical properties

Gold is a yellow cubic metal. Lump gold gives a yellow reflected color, gold foil of an especially thin workmanship can be blue or green in transmission, gold vapors are greenish-yellow. Colloidal solutions with gold content have different colors, it all depends on the degree of dispersion (for example, when gold compounds get on human skin, a colloid with a violet color is formed).

The formula in the form of text is: Au. The molecular weight of gold is (in amu) 196.97. The melting point of the metal (in degrees Celsius) is 1063.4 o, the boiling point (in degrees Celsius) is 2880 o. Solubility of gold (in g / 100 g or characteristic): almost insoluble in distilled water; in mercury - 0.13 (at a temperature of 18 o C); almost insoluble in ethanol.

The gold content in the composition of the earth's crust (solid) is 0.0000005%. In nature, it is found only in its native form (the largest nugget in the world weighed 112 kilograms). Gold minerals are known for the most part of telluride nature, for example, calaverite, creinerite, ilvanite, aurostibite, petzite. The average gold content of the deposits is 0.001%. In the water of the world's oceans, the content of dissolved gold is 0.0000000005% (it is poisoned in the ocean when seawater is ingested). If we consider living organisms, then most of the gold is found in the grains, stems and leaves of corn.

The density of gold as a metal is 19.3 (at a temperature of 20 o C, g / cm3). The value of the pressure of gold vapor (in mm Hg) is 0.01 (at a temperature of 1403 o C), 0.1 (at a temperature of 1574 o C), 10 (at a temperature of 2055 o C) 100 (at a temperature of 2412 o C) The index of the surface tension of the metal (in mN / m) is 1120 (at a temperature of 1200 o C). The specific heat of the metal while maintaining a constant pressure (in J / g · K) is 0.132 (at a temperature of 0-100 o C). The standard enthalpy of formation of gold ΔH (298 K, kJ / mol) is 0 (t). The index of the standard Gibbs energy of formation ΔG (298 K, kJ / mol) is 0 (t). The value of the standard entropy of formation S (298 K, J / mol · K) is 47.4 (t). The standard molar heat capacity of gold Cp (298 K, J / mol · K) is 25.4 (t). The index of the enthalpy of melting of gold ΔHmelt (kJ / mol) is 12.55. Well, the enthalpy of boiling gold ΔHboil (kJ / mol) is 348.5.

Gold has high ductility, malleability, and thermal and electrical conductivity. Gold is well welded and soldered (on amalgam). Gold reflects infrared radiation. Naturally occurring gold has one isotope, Au-197. The Mohs hardness index of gold is 2.5. Pure gold is soft.

Gold is one of the heaviest metals: the density of the metal, as mentioned above, is 19.3 g / cm3. Osmium, iridium, platinum and rhenium have a greater mass than gold.

Chemical properties

Gold is an inert metal, under normal conditions gold does not react with most acids, does not form oxides, which is why it belongs to noble metals, but unlike ordinary metals, which are destroyed by the environment. It was discovered that aqua regia dissolves gold, and this shaken the confidence in the inertness of the metal.

Over the millennia, chemists have conducted many different experiments with gold, as a result, it turned out that gold is not as inert as non-specialists think about it. But here, sulfur and oxygen (which are aggressive towards almost all metals, especially after heating), do not affect gold at any temperature. The only exception is surface gold atoms. Upon reaching 500–700 o C, the atoms form a thin but highly stable oxide, which does not decompose within 12 hours when heated to 800 o C. For example, Au 2 O 3 or AuO (OH). This oxide layer was found on the surface of native gold.

Gold does not react with nitrogen, hydrogen, carbon, phosphorus, and when heated, halogens react with gold, forming AuBr 3, AuF 3, AuCl 3, and AuI. It is easy, even at room temperature, to react with bromine and chlorine water. Chemists meet with these reagents. The danger for gold rings in everyday life is iodine tincture, i.e. aqueous-alcoholic solution of iodine and potassium iodide: 2Au + I 2 + 2KI = 2K.

Among standard potentials, gold is located to the right of hydrogen, which is why it does not react with non-oxidizing acids. Gold dissolves in heated selenic acid:

2Au + 6H 2 SeO 4 = Au 2 (SeO 4) 3 + 3H 2 SeO 3 + 3H 2 O,

In also in concentrated hydrochloric acid in the process of passing through a chlorine solution:

2Au + 3Cl 2 + 2HCl = 2H

If the resulting solution is evaporated, it becomes possible to obtain crystals of hydrochloric acid HAuCl 4 3H 2 O.

After reduction of gold salts with tin dichloride, a persistent, bright red colloidal solution (ie "cassian purple") is formed. Some gold oxides (eg, AuO 2 and Au 2 O 3) can only be obtained by vaporizing the metal at a high temperature in a vacuum. Hydroxide Au (OH) 3 under the action of especially strong alkalis precipitates in the form of a solution of AuCl 3. Salt Au (OH) 3 with a base - aurat - are formed when it is dissolved in strong alkalis. Gold reacts with hydrogen, forming a hydride, upon reaching a pressure of 28 - 65 * 10 -8 Pa and a temperature of more than 3500 o C. Sulfoaurate MeAuS is formed in the reaction of gold with hydrosulfide of alkali metals at a high temperature. There are gold sulfides Au 2 S and Au 2 S 3, but they are metastable, decompose, separating a metallic phase.

Gold is dissolved in aqua regia: Au + HNO 3 + 4HCl = H + NO + 2H 2 O. After evaporation of the solution, crystals of hydrochloric acid HAuCl 4 able to dissolve gold. In sulfuric acid, gold can dissolve with oxidants: iodic acid, nitric acid, manganese dioxide. In cyanide solutions with oxygen access, gold dissolves, forming very strong dicyanoaurates: 4Au + 8NaCN + 2H 2 O + O 2 = 4Na + 4NaOH; this reaction underlies a very important industrial method of recovering ore gold.

There are organic compounds of gold. The action of gold (III) chloride with aromatic compounds produces compounds that are resistant to oxygen, water and acids, for example: AuCl 3 + C 6 H 6 = C 6 H 5 AuCl 2 + HCl. Organic derivatives of metal (I) are stable in the presence of ligands coordinated to gold, for example, triethylphosphine: CH 3 Au · P (C 2 H 5) 3.

Using materials from the website