There is an opinion that gold itself is one of the least useful metals. Is it so? An erudite engineer of the early 20th century. would answer: “Undoubtedly, so.” Engineers of the mid-70s were not so categorical. The technology of the past did without gold not only because it was too expensive. There was no particular need for properties unique to gold. However, the statement that these properties were not used at all would be incorrect. Church domes were gilded because of the chemical resistance and ease of mechanical processing of gold. Modern technology also uses these properties.

Gold and its alloys

Gold is a very soft metal, it can be easily flattened and turned into the thinnest plates and sheets. In some cases this is very convenient. Despite this, most gold products are cast, although the melting point of gold is 1063° C. Even the masters of antiquity had to make sure that it was not possible to give gold all the necessary shapes by casting. When making, for example, an ordinary jug, the handle had to be cast separately and then soldered.
Historians and archaeologists have found that soldering metals has been known to people for several millennia. Only the ancients soldered not with tin, but with gold, or rather, an alloy of gold and silver. Modern technology also sometimes has to use gold solder.
In terms of electrical conductivity, gold ranks third after silver and copper.
When gold comes into contact with copper under pressure in a reducing environment or in a vacuum, the process of diffusion - the penetration of molecules of one metal into another - occurs quite quickly. Parts made of these metals are connected to each other at a temperature significantly lower than the melting point of copper, gold or any of their alloys. Such connections are called golden seals. They are used in the manufacture of some types of radio tubes, although the strength of gold seals is somewhat lower than the strength of compounds obtained by alloying. Alloys of gold with silver or copper are used to make the hairs of galvanometers and other precision instruments, as well as miniature electrical contacts designed to receive a huge number of short circuits and open circuits. Moreover, what is especially important is that these structurally simple parts must work without sticking contacts and must respond to every impulse.
In alloys that provide the least adhesion, gold plays a special role. Alloys of gold with palladium (30%) and platinum (10%), palladium (35%) and tungsten (5%), zirconium (3%), manganese (1%) work flawlessly. Special literature describes alloys with similar properties that can compete with gold. This is, for example, an alloy of platinum with 18% iridium, but it is more expensive than any of the listed alloys. And all the best contact alloys are very expensive, but modern space technology cannot do without them. In addition, they are used in the most important non-spacecraft, which require special reliability.
Gold and its alloys have become a construction material not only for miniature radio tubes and contacts, but also for giant particle accelerators. An accelerator, as a rule, is a huge annular chamber - a pipe rolled into a bagel. The greater the vacuum that can be created in such a pipe, the longer elementary particles can live in it. The pipes are made of stainless steel melted in a vacuum. The inner surface of the pipe is polished to a mirror shine - with such a surface it is easier to maintain a deep vacuum.
The pressure in the particle accelerator does not exceed billionths of atmospheric pressure. There is no need to explain how difficult it is to maintain such a vacuum in a giant steering wheel, especially since the steering wheel has bends, sleeves, and joints.
O-rings and washers for accelerators are made of soft, ductile gold. The camera joints are soldered with gold.
In some cases, the plasticity of gold turns out to be an irreplaceable quality, while in others, on the contrary, it creates difficulties. One of the oldest uses of gold is in dentures. Of course, soft metal is easier to give the desired shape, but teeth made of pure gold wear out relatively quickly. Therefore, dentures and jewelry are made not from pure gold, but from its alloys with silver or copper. Depending on the silver content, such alloys have different colors: with 20-40% silver the metal is greenish-yellow, with 50% it is pale yellow.
The alloys are further strengthened by heat treatment, and at the same time gold behaves in a very unique way. The process of hardening steel is well known: the metal is heated to a certain temperature and then quickly cooled. This treatment imparts hardness to the steel. To remove the hardening, the metal is reheated and cooled slowly - this is annealing. Alloys of gold with copper and silver, on the contrary, acquire softness and ductility with rapid cooling, and with slow annealing - hardness and brittleness.

Gilding

Gold is one of the heaviest metals, only osmium, iridium and platinum surpass it in density. If the pharaohs' litters were truly gold, they would be two and a half times heavier than the iron ones. The stretcher was made of wood, covered with the finest gold foil.
An interesting detail: the density of tungsten is almost the same as the density of gold. In ancient times, tungsten was not known, but if we assume that the golden crown of the Syracusan king Hieron would have been counterfeited not with silver, but with tungsten, then the great Archimedes, using the law he derived, would not have been able to detect the fakes and convict the fraudulent master.
Gold coatings have been known since ancient times. The thinnest sheets of gold were glued to wood, copper, and later to iron with special varnishes. On items in constant use, such gold plating lasted for about 50 years. True, this method of gilding was not the only one. In some cases, the product was covered with a layer of special glue and sprinkled with the finest gold powder.
Since the middle of the last century, after the Russian scientist B. S. Jacobi discovered the processes of electroplating and electroplating, the old methods of gilding have almost fallen out of use. The electroplating process is not only more productive, it allows you to give the gold plating different shades. The addition of a small amount of copper cyanide to the gold electrolyte gives the coating a red tint, and in combination with silver cyanide it gives a pink tint: using silver cyanide alone you can get a greenish tint to gold coatings.
Gold coatings are highly durable and reflect light well. Nowadays, parts of conductors in high-voltage radio equipment and individual parts of X-ray machines are subjected to gilding. Reflectors are made with gold coating for drying by infrared rays. The surface of several artificial Earth satellites was gold-plated: gilding protected the satellites from corrosion and excess heat.
The newest method of applying gold coatings is catoid sputtering. An electric discharge in a discharged gas is accompanied by destruction of the cathode. In this case, the cathode particles fly at enormous speed and can be deposited not only on metal, but also on other materials: paper, wood, ceramics, plastic. This method of obtaining the thinnest gold coatings is used in the manufacture of solar cells, special mirrors and in some other cases.

Paints of gold

The “nobility” of gold extends only to certain limits. In other words, its compounds with other elements can be obtained relatively easily. Even in nature there are ores in which gold is not found in a free state, but in combination with tellurium or selenium.
The industrial process of extracting gold from ores - cyanidation - is based on the interaction of gold with alkali metal cyanides:
4Au + 8KCN + 2H 2 O + O 2 → 4K + 4KON.
Another important process - chlorination (it is now used not so much for extraction as for refining gold) - is based on the interaction of gold with chlorine.
Some gold compounds have industrial applications. First of all, it is gold chloride AuCl 3, formed when gold is dissolved in aqua regia. Using this compound, high-quality red glass - golden ruby ​​- is obtained. Such glass was first made at the end of the 17th century by Johann Kunkel, but a description of the method for its production appeared only in 1836. A solution of gold chloride is added to the charge and, by changing the latter, glass with various shades is obtained - from soft pink to dark purple. The best colors for glass are those that contain lead oxide. True, in this case one more component has to be introduced into the charge - a clarifier, 0.3-1.0% of “white arsenic” As 2 0 3. Coloring glass with gold compounds is not very expensive - for uniform, intense coloring of the entire mass, no more than 0.001-0.003% AuCl 3 is needed.
You can also give glass a red color by introducing compounds of copper or selenium and cadmium into the charge. They are, of course, cheaper than gold compounds, but working with them and obtaining high-quality products with their help is much more difficult. The production of “copper ruby” is complicated by the variability of color: the shade greatly depends on the cooking conditions. The difficulty in obtaining “selenium ruby” is the burning of selenium and sulfur from cadmium sulfide, which is part of the charge. “Golden Ruby” does not lose color when treated at high temperatures. The undeniable advantage of the method for producing it is that unsuccessful cooking can be corrected by subsequent remelting. As a coloring agent, gold chloride is also used when painting on glass and porcelain. In addition, it has long been used as a toning reagent in photography. “Gold Fixer” gives photo prints black-violet, brown or purple-violet shades. For the same purposes, another gold compound is sometimes used - sodium chloroaurate NaAuCl 4.

Gold in medicine

First attempts to use gold for medical purposes date back to the times of alchemy, but they were little more successful than the search for the philosopher's stone. In the 16th century Paracelsus tried to use gold preparations to treat certain diseases, in particular syphilis. “It is not the transformation of metals into gold that should be the goal of chemistry, but the preparation of medicines,” he wrote.
Much later, compounds containing gold were proposed as a medicine against tuberculosis. It would be wrong to consider that this proposal is devoid of reasonable grounds: in vitro, that is, outside the body, “in a test tube,” these salts have a detrimental effect on the tuberculosis bacillus, but to effectively combat the disease, a fairly high concentration of these salts is needed. Nowadays, gold salts are important for the fight against tuberculosis only insofar as they increase resistance to the disease.
It was also found that gold chloride at a concentration of 1:30,000 begins to inhibit alcoholic fermentation, with an increase in concentration to 1:3900 it significantly inhibits it, and at a concentration of 1:200 it completely stops.
A more effective medical remedy turned out to be gold and sodium thiosulfate AuNaS 2 0 3, which is successfully used to treat an intractable skin disease - erythematous lupus. Organic gold compounds, primarily crizolgan and triphal, also began to be used in medical practice.
Crizolgan was at one time widely used in Europe to combat tuberculosis, and triphal, less toxic and more effective than gold and sodium thiosulfate, was used as a cure for erythematous lupus. In the Soviet Union, a highly active drug was synthesized - crizanol (Au-S-CH 2 -CHOH-CH 2 S0 3) 2 Ca for the treatment of lupus, tuberculosis, and leprosy.
After the discovery of radioactive isotopes of gold, its role in medicine increased significantly. Colloidal isotope particles are used to treat malignant tumors. These particles are physiologically inert and therefore do not need to be removed from the body as quickly as possible. Injected into specific areas of the tumor, they irradiate only the affected areas. Radioactive gold can cure some forms of cancer. A special “radioactive pistol” has been created, the clip of which contains 15 rods of radioactive gold with a half-life of 2.7 days. Practice has shown that treatment with “radioactive needles” makes it possible to eliminate a superficial breast tumor already on the 25th day.

Gold catalysis

Radioactive gold has found application not only in medicine. In recent years, reports have appeared about the possibility of replacing platinum catalysts in several important petrochemical and chemical processes.

Particularly interesting are the prospects for using the catalytic properties of gold in the engines of high-speed aircraft. It is known that above 80 km the atmosphere contains quite a lot of atomic oxygen. The combination of individual oxygen atoms into a 0 2 molecule is accompanied by the release of a large amount of heat. Gold catalytically speeds up this process.

It is difficult to imagine a super-fast aircraft operating virtually without fuel, but such a design is theoretically possible. The engine will operate using the energy released during the dimerization reaction of atomic oxygen. Having risen to an altitude of 80 km (i.e., significantly exceeding the ceiling of modern aircraft), the pilot will turn on the oxygen-catalytic engine, in which atmospheric oxygen will come into contact with the catalyst.

Of course, it is still difficult to predict what characteristics such an engine will have, but the idea itself is very interesting and, apparently, not fruitless. On the pages of foreign scientific journals, possible designs of the catalytic chamber were discussed, and even the inappropriateness of using a finely dispersed catalyst was proven. All this indicates the seriousness of intentions. Perhaps such engines will be used not on airplanes, but on rockets, or perhaps further research will bury this idea as impracticable. But this fact, like everything discussed above, shows that the time has come to abandon the established view of gold as a metal useless for technology.

ON A GOLD BACKING. In the nuclear fusion of mendelevium, the target was gold foil onto which an insignificant amount (only about a billion atoms) of einsteinium was deposited electrochemically. Gold substrates for nuclear targets were also used in the synthesis of other transuranium elements.

SATELLITES OF GOLD. Nuggets are rarely pure gold. They usually contain quite a lot of copper or silver. In addition, native gold sometimes contains tellurium.

GOLD OXIDIZES. At temperatures above 100°C, an oxide film forms on the surface of gold. It does not disappear upon cooling; at 20°C the film thickness is approximately 30 A°.

MORE ABOUT GOLDEN PAINTS. At the end of the last century, chemists first managed to obtain colloidal solutions of gold. The color of the solutions turned out to be purple. And in 1905, by treating weak solutions of gold chloride with alcohol, they obtained colloidal solutions of blue and red gold. The color of the solution depends on the size of the colloidal particles.

GOLD IN FIBER PRODUCTION. Threads of artificial and synthetic fibers are produced in devices called spinnerets. The material of the spinnerets must be resistant to the aggressive environment of the spinning solution and sufficiently durable. In the production of nitron, dies made of platinum, to which gold is added, are used. By adding gold, two goals are achieved: the dies become cheaper (since platinum is more expensive than gold) and stronger. Both metals in their pure form are soft, but in an alloy they are not only a material of increased strength, but even springy.

GOLDEN BULLET. The President of the Republic was shot dead. The murderer received a stipulated reward from those who sent him. Proof that it was he who carried out the “assignment” was supposed to be a newspaper report that the bullet that killed the president was gold. This is the plot of the famous film of the same name. However, gold bullets appear to have been used before in less dramatic situations. In the first half of the last century, the merchant Shelkovnikov traveled from Irkutsk to Yakutsk. From conversations at the Krestovaya parking lot, he learned that the Tungus (Evenks), who hunt animals and birds, buy gunpowder at a trading post and mine lead themselves. It turns out that along the bed of the Tonguda River you can collect a lot of “soft yellow stones” that are easy to round, but they are as heavy in weight as lead. The merchant realized that we were talking about placer gold, and soon gold mines were organized in the upper reaches of this river.

GOLDEN SIEVE. It is known that gold can be rolled into the thinnest, almost transparent sheets, bluish when exposed to light. In this case, tiny pores are formed in the metal, which could serve as a molecular sieve. The Americans tried to make an installation for separating uranium isotopes on gold molecular sieves, turning several tons of the precious metal into the thinnest foil, but things didn’t go any further. Either the sieves turned out to be insufficiently effective, or a cheaper technology was developed, or they simply regretted the gold - one way or another, but the foil was again melted into ingots.

AGAINST HYDROGEN FRITTLE. When steel comes into contact with hydrogen, especially at the moment the latter is released, the gas “introduces” itself into the metal, making it brittle. This phenomenon is called hydrogen embrittlement. To eliminate it, parts of the devices, and sometimes the entire device, are covered with a thin layer of gold. This, of course, is expensive, but we have to take such a measure, since gold protects steel from hydrogen better than any other coating, and the damage from hydrogen embrittlement is quite large...

STORY WITH THE DUELIST. The famous inventor Ernst Werner Siemens fought a duel in his youth, for which he was imprisoned for several years. He managed to obtain permission to set up a laboratory in his cell and continued experiments in electroplating technology in prison. In particular, he developed a method for gilding non-precious metals. When this task was already close to being resolved, the pardon came. But, instead of rejoicing at the freedom he finally received, the prisoner submitted a request to remain in prison for some more time - so that he could finish the experiments. The authorities did not respond to Siemens’ request and kicked him out of the “habitable premises.” He had to re-equip the laboratory and finish what he started in prison when he was free. Siemens did receive a patent for the gilding method, but this happened later than it could have been.

GOLD IN BIRCH JUICE. Gold is not one of the vital elements. Moreover, its role in living nature is very modest. However, in 1977, in the journal “Reports of the Academy of Sciences of the USSR” (vol. 234, No. I), a message appeared that in the sap of birch trees growing above gold deposits, there is an increased content of gold, as well as zinc, if under The soil hides deposits of this by no means noble metal.

CONTRAINDICATIONS. It would seem that medical preparations of gold, a chemically passive element, should be drugs without contraindications or almost without contraindications. However, it is not. Gold preparations often cause side effects - fever, irritation of the kidneys and intestines. In severe forms of tuberculosis, diabetes mellitus, diseases of the blood, cardiovascular system, liver and some other organs, the use of drugs with gold can do more harm than good.

Before talking about the properties of any precious metal, you need to understand and determine its chemical composition, as well as understand its physical properties. Therefore, the answer to the question “what is gold made of” should be sought first of all in school chemistry lessons or on the Internet, and only then can one judge the corresponding price of a metal with unique properties. After all, the high cost of this substance appeared for a reason.

Composition of precious metal in nature

The thing is that the reasons and processes for the appearance of gold on Earth are unknown to science. There are some assumptions about the ingress of precious metal particles due to the action of meteorites and nuclear reactions during neutron explosions, but these are only hypotheses. The fact remains that there is very little gold on Earth; every day people mine such an amount of iron that is equal to all the gold mined during the existence of civilization.

Gold nuggets

Therefore, scientists and alchemists had questions about the structure of this metal, and were also interested. If you know the exact structure, you can make assumptions about the appearance of gold, and only then try to conduct an experiment and obtain gold in the laboratory.

So, in nature this element occurs in the form of gold particles. According to scientists, the lithosphere contains about 5% gold. But according to hypotheses, there is much more of it in the Earth’s core. Gold can be found in igneous rocks, as well as at broken tectonic plates or in old mountain ranges.

This location is practically not explained by geologists, and astrophysicists consider this phenomenon to be a consequence of the largest meteorite attacks on certain areas of the earth. But, thanks to temperature changes, gold from deeper balls comes to the surface. And then it can be found in iron ores.

In ores, gold is present in inclusions or veins measuring 0.1-1000 microns. It is rare to find one weighing several kilograms. And precious metal can be extracted from the following types of ores:

• gold ores, which are very rare;
• iron ores, in which the lowest in comparison with other mines;
• copper ores;
• lead-zinc ores;
• uranium mines.

It is interesting that along with gold you can find impurities of such elements as:

• bismuth;
• antimony;
• selenium.

But silver is never found next to gold deposits. Sometimes deposits are found even under ordinary soil on different continents.

Physical and chemical capabilities of the element

From the point of view of chemists, gold is one of the elements of the periodic table. The chemical formula consists of the abbreviation Au from the word aurum. The whole point is that this precious metal consists of isotopes of one substance and there is simply no formula in the usual sense. The atomic mass of gold is 196.9 g/mmol. It was included in the group of noble metals after checking its interaction with other elements, as well as with ordinary oxygen.

It turned out that gold does not react at all to either sulfur or oxygen, like most other elements. Even if gold reacts, this means that only the outer layer of the metal will be damaged, but not the entire substance.

In addition, gold has an attractive appearance, and it is also ductile, which makes it possible to make various jewelry from gold and conducts current well. Even mineral acids cannot change the appearance and composition of gold. Thanks to this, the authenticity of the metal is determined.

They indicate that in terms of composition it is a unique element in the periodic table. To look at the particles of gold that are part of the jewelry, you need to evaporate the product in aqua regia. This is how refining is carried out, that is, the process of extracting gold from impurities.

Physical characteristics of gold

Nothing can be extracted from the metal itself; gold is an integral element. But manufacturers have a question about how to extract gold from ore on an industrial scale and purify it from impurities. A solution to this issue can be found using processes such as:

• concentration flotation, gravity;
• leaching;
• sorption;
• cyanidation;
• amalgamation.

All these processes are carried out in stages and are now mechanized. A few centuries ago, gold mining was done manually without the slightest hint of automation of the process. This was possible due to another feature of gold - its high density. Therefore, when washed out of rivers, gold settled to the very bottom, where it could be seen. It should also be remembered that the compounds of gold with other metals or elements are unstable, so the precious metal can be extracted chemically. The final stages involve dissolving the resulting gold in aqua regia and subsequent precipitation of the precious metal.

The presence of precious metal in the composition of the product is detected through the formation of colored sediments and solutions. To do this, they use gold compounds with various substances, as well as processes such as electrophoresis, chromatography, and luminescence. To determine the amount of gold in a substance, titration, photometry, and gravimetry methods are used.

Impurities are also sometimes added to gold itself. This is done in order to reduce the cost of the product, as well as give it the necessary shape. The thing is that gold is a soft metal. This is not critical when producing ingots, which, due to their shape, do not deform greatly over time. But gold jewelry may well bend under its own weight or change the design for the worse.

Therefore, in order for the earrings or chain to remain unchanged, other metals are added to the composition, which are called alloys. A ligature is an admixture to gold, so not only the cost of the product, but also its characteristics will depend on its properties. For example, the type of metal changes the shade of the jewelry. If gold in its pure form has a bright yellow color, then with the addition of copper the product will acquire a red tint. Gold is called: red, yellow, white, pink. The most commonly used ligatures are:

• Copper. It adds strength to the composition of the decoration.
• Silver. The precious metal acquires a noble hue.
• Platinum is an even more expensive metal than gold.
• Nickel. It improves the casting quality of the product, but the alloy with nickel is not suitable for making jewelry.
• Zinc lowers the melting point, but adds brittleness to the alloy.
• Cadmium and palladium are rarely added to gold alloys in practice.

Such gold with admixtures of other metals in its composition has a fineness or carat. Knowing the sample of the product, you can determine the content of pure gold in it. This is not difficult, since gold items certified and manufactured according to the rules must have a mark on which the purity will be indicated. Sample compositions are determined according to GOST. All proportions must be strictly observed, because the cost of the product depends on this.

According to GOST standards, there are about 40 alloys of different samples. The percentage of gold depends on the purpose of using the precious metal. Of course, high-grade gold is used to make jewelry, which looks presentable. But in industry, low-grade alloys that have the necessary physical properties can also be used.

No one can unravel the formula of gold to this day, but many admire this metal and continue to make a cult of their lives out of it. But the formula of the precious metal, and therefore its true composition, still remains one of the questions to which humanity does not yet have an exact answer.

GOLD (chemical element) GOLD (chemical element)

GOLD (lat. Aurum ) , Au (pronounced "aurum"), chemical element with atomic number 79, atomic mass 196.9665. Known since ancient times. There is one stable isotope in nature, 197 Au. Configuration of outer and pre-outer electron shells 5 s 2 p 6 d 10 6s 1 . Located in group IB and the 6th period of the periodic table, it belongs to the noble metals. Oxidation states 0, +1, +3, +5 (valency from I, III, V).
The metallic radius of the gold atom is 0.137 nm, the radius of the Au + ion is 0.151 nm for coordination number 6, the Au 3+ ion is 0.084 nm and 0.099 nm for coordination numbers 4 and 6. Ionization energies Au 0 - Au + - Au 2+ - Au 3 + are respectively equal to 9.23, 20.5 and 30.47 eV. Electronegativity according to Pauling (cm. PAULING Linus) 2,4.
Being in nature
The content in the earth's crust is 4.3·10–7% by mass, in the water of the seas and oceans it is less than 5·10–6% mg/l. Refers to scattered elements. More than 20 minerals are known, of which the main one is native gold (electrum, cuprous, palladium, bismuth gold). Large nuggets are extremely rare and, as a rule, have personal names. Chemical compounds of gold are rare in nature; they are mainly tellurides - caleverite AuTe 2, krennerite (Au,Ag)Te 2 and others. Gold may be present as an impurity in various sulfide minerals: pyrite (cm. PYRITE), chalcopyrite (cm. CHALCOpyRITE), sphalerite (cm. SPHALERITE) and others.
Modern methods of chemical analysis make it possible to detect the presence of minute amounts of Au in plant and animal organisms, in wines and cognacs, in mineral waters and in sea water.
History of discovery
Gold has been known to mankind since ancient times. Perhaps it was the first metal with which man became acquainted. There is evidence of the mining of gold and the manufacture of products from it in Ancient Egypt (4100-3900 BC), India and Indochina (2000-1500 BC), where it was used to make money, expensive jewelry, and works of art. cult and art.
Receipt
Sources of gold for its industrial production are ores and sands of placer and primary gold deposits, the gold content of which is 5-15 g per ton of source material, as well as intermediate products (0.5-3 g/t) of lead-zinc, copper, uranium and some other industries.
The process of obtaining gold from placers is based on the difference in the densities of gold and sand. Using powerful jets of water, the crushed gold-bearing rock is transferred to a state suspended in water. The resulting pulp flows down an inclined plane in a dredge. In this case, heavy gold particles settle, and grains of sand are carried away by water.
In another way, gold is extracted from ore by treating it with liquid mercury and obtaining a liquid alloy - amalgam. Next, the amalgam is heated, the mercury evaporates, and the gold remains. The cyanide method of extracting gold from ores is also used. In this case, the gold ore is treated with a solution of sodium cyanide NaCN. In the presence of atmospheric oxygen, gold goes into solution:
4Au + O 2 + 8NaCN + 2H 2 O = 4Na + 4NaOH
Next, the resulting solution of the gold complex is treated with zinc dust:
2Na + Zn = Na 2 + NO +H 2 O
followed by selective precipitation of gold from solution, for example, using FeSO 4 .
Physical and chemical properties
Gold is a yellow metal with a face-centered cubic lattice ( a= 0.40786 nm). Melting point 1064.4 °C, boiling point 2880 °C, density 19.32 kg/dm3. It has exceptional ductility, thermal conductivity and electrical conductivity. A ball of gold with a diameter of 1 mm can be flattened into the thinnest sheet, translucent in a bluish-green color, with an area of ​​50 m2. The thickness of the thinnest gold leaves is 0.1 microns. The finest threads can be drawn from gold.
Gold is stable in air and water. With oxygen (cm. OXYGEN), nitrogen (cm. NITROGEN), hydrogen (cm. HYDROGEN), phosphorus (cm. PHOSPHORUS), antimony (cm. ANTIMONY) and carbon (cm. CARBON) does not interact directly. Antimonide AuSb 2 and gold phosphide Au 2 P 3 are obtained indirectly.
In the series of standard potentials, gold is located to the right of hydrogen, therefore it does not react with non-oxidizing acids. Dissolves in hot selenic acid:
2Au + 6H 2 SeO 4 = Au 2 (SeO 4) 3 + 3H 2 SeO 3 + 3H 2 O,
in concentrated hydrochloric acid when passing through a chlorine solution:
2Au + 3Cl2 + 2HCl = 2H
By carefully evaporating the resulting solution, yellow crystals of chlorauric acid HAuCl 4 3H 2 O can be obtained.
With halogens (cm. HALOGEN) Without heating and in the absence of moisture, gold does not react. When gold powder is heated with halogens or xenon difluoride, gold halides are formed:
2Au + 3Cl 2 = 2AuCl 3,
2Au + 3XeF 2 = 2AuF 3 + 3Xe
Only AuCl 3 and AuBr 3, consisting of dimeric molecules, are soluble in water:
The thermal decomposition of hexafluoroaurates (V), for example, O 2 + –, produced gold fluorides AuF 5 and AuF 7 . They can also be obtained by oxidizing gold or its trifluoride with KrF 2 and XeF 6 .
Gold monohalides AuCl, AuBr and AuI are formed by heating the corresponding higher halides in vacuum. When heated, they either decompose:
2AuCl = 2Au + Cl2
or disproportionate:
3AuBr = AuBr 3 + 2Au.
Gold compounds are unstable and hydrolyze in aqueous solutions, easily being reduced to metal.
Gold (III) hydroxide Au(OH) 3 is formed by adding alkali or Mg(OH) 2 to a solution of H:
H + 2Mg(OH) 2 = Au(OH) 3 Ї + 2MgCl 2 + H 2 O
When heated, Au(OH) 3 easily dehydrates, forming gold(III) oxide:
2Au(OH) 3 = Au 2 O 3 + 3H 2 O
Gold(III) hydroxide exhibits amphoteric properties when reacting with solutions of acids and alkalis:
Au(OH) 3 + 4HCl = H + 3H 2 O,
Au(OH)3 + NaOH = Na
Other oxygen compounds of gold are unstable and easily form explosive mixtures. The compound of gold (III) oxide with ammonia Au 2 O 3 ·4NH 3 is “explosive gold” and explodes when heated.
When gold is reduced from dilute solutions of its salts, as well as when gold is electrically sputtered in water, a stable colloidal solution of gold is formed:
2AuCl 3 + 3SnCl 2 = 3SnCl 4 +2Au
The color of colloidal solutions of gold depends on the degree of dispersion of gold particles, and the intensity depends on their concentration. Gold particles in solution are always negatively charged.
Application
Gold and its alloys are used for the manufacture of jewelry, coins, medals, dentures, parts of chemical equipment, electrical contacts and wires, microelectronics products, for cladding pipes in the chemical industry, in the production of solders, catalysts, watches, for coloring glass, making feathers for fountain pens, coating of metal surfaces. Typically, gold is used in an alloy with silver or palladium (white gold; also called an alloy of gold with platinum and other metals). The gold content in the alloy is designated by the state mark. 14k gold is an alloy with 58.3% gold by weight. See also Gold (in economics) (cm. GOLD (in economics)).
Physiological action
Some gold compounds are toxic and accumulate in the kidneys, liver, spleen and hypothalamus, which can lead to organic diseases and dermatitis, stomatitis, thrombocytopenia.

encyclopedic Dictionary. 2009 .

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- (French Chlore, German Chlor, English Chlorine) an element from the group of halogens; its sign is Cl; atomic weight 35.451 [According to Clarke's calculation of Stas data.] at O ​​= 16; Cl 2 particle, which is well matched by its densities found by Bunsen and Regnault in relation to... ...

- (chemical; Phosphore French, Phosphor German, Phosphorus English and Lat., whence the designation P, sometimes Ph; atomic weight 31 [In modern times, the atomic weight of Ph. was found (van der Plaats) to be: 30.93 by restoration with a certain weight of F. metal... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Ephron

- (Argentum, argent, Silber), chemical. Ag sign. S. is one of the metals known to man since ancient times. In nature, it is found both in the native state and in the form of compounds with other bodies (with sulfur, for example Ag 2S... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Ephron

- (Argentum, argent, Silber), chemical. Ag sign. S. is one of the metals known to man since ancient times. In nature, it is found both in the native state and in the form of compounds with other bodies (with sulfur, for example Ag2S silver ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Ephron

Hello! Gold is a chemical element that has claimed many lives. During the construction of St. Isaac's Cathedral in St. Petersburg, the domes were gilded using gold amalgam. Architect Auguste Montferrand took measures to protect workers from mercury vapor, but knew they were doomed. But the domes will never have to be gilded again.

And so it happened: all 60 people died from poisoning, and the cathedral has never been gilded since then.

A cubic kilometer of sea water contains 5 kg of the coveted element, and if you prick your finger and squeeze out a drop of blood, it will contain 0.00025 mg of gold. 10 mg is contained in the human skeleton: if you set out to melt a ring of people, you will only need 300 people. But this gold is in such a dispersed form in the environment that it is unprofitable and often impossible to extract it from there.

Deposits suitable for gold mining are primary (post-magmatic) and secondary (placer).

Primary deposits

Magma, the melt inside the globe, is rich in the chemical element Au. Gold is found in the upper layers of the mantle and partially in the earth's crust (however, it contains almost the entire periodic table). Magma comes to the surface of the planet, cools and turns into solid rock. The places where it contains enough of the precious element to justify industrial development are primary deposits.

Natural gold is found in the form of nuggets - whole grains of a chemically pure substance. It is often combined with other elements (magma contains almost everything):

• silver;
• copper;
• platinum group metals;
• bismuth and others.

Secondary deposits

Secondary deposits are the result of the destruction of primary ones, the so-called weathering, which happens:

• physical (cause - wind, water, temperature fluctuations);
• chemical (chemical reactions);
• biological (bacteria and other organisms).

A placer of pure gold looks like sand and sometimes drifts along waters many kilometers from the original deposit.

History of element discovery

In its pure form, gold fell into the hands of man in the 6th century BC. Massive development of African deposits began earlier - around 2000 BC. e., but there were no methods for getting rid of impurities, and gold products of that time are of low standard.

During late antiquity (beginning of our era), alchemy began to spread throughout the world with its desire to transform base chemical elements into noble ones. She was not successful, but thanks to her, modern civilization has mastered many miracles - for example, the technique of extracting chemically pure gold from ore.

The Latin name for gold is Aurum (read as aurum) - “yellow”. It is accepted as international. The symbol of the sun among alchemists looked like a circle with a dot inside, and in modern chemistry it is denoted by the abbreviation Au.

How do you get it?

The main methods for producing gold on an industrial scale complement each other - for example, concentrate can be purified from dense impurities by amalgamation.

Flushing

Washing (sizing) is an ancient method of extraction from secondary deposits. Sand is washed away due to its density: less dense minerals are washed out with water, and the concentrate settles.

Large-scale gold mining is automated: instead of people, washing devices and excavators work. However, the principle of their operation has remained almost unchanged over the past 2000 years.

The concentrate is not pure gold. There are elements that are denser - they settle with sand at the bottom of the washing tank. For final cleaning, other methods, in particular chemical ones, are used.

Amalgamation

This method has also been known since antiquity, but was described in the 16th century. It is possible due to the property of mercury to form alloys (amalgams) with other metals without additional thermal or chemical effects. After getting rid of waste rock fragments, the chemical elements are mechanically separated.

Expert opinion

Vsevolod Kozlovsky

6 years in jewelry making. Knows everything about samples and can identify a fake in 12 seconds

Amalgamation is not used everywhere: in a number of countries (since 1988 - in Russia) the use of mercury is prohibited due to the deadly danger of this element to humans.

Cyanidation

The method of extracting a precious element from ore by cyanidation is based on the ability of gold to dissolve in hydrocyanic acid (hydrogen cyanide, HCN) and its salts. The ore is treated with a weak (0.03–0.3%) cyanide solution. The noble metal reacts before other chemical elements, and after the chemical reaction it precipitates from solution.

Physical and chemical properties

: in its pure form does not form oxides, is not subject to corrosion. He also has:

• high density - 19.32 g/cm³;
• medium melting point (melting point in the range of 600–1600 °C - 1064.43 °C);
• low hardness - 2.5 points on the Mohs scale;
• high malleability (thanks to it, gilding is created);
• high plasticity, ductility.

Gold's place in Mendeleev's periodic table

The element is located in group XI (copper subgroup), period VI of the periodic table of chemical elements.

The atomic number (charge number) of gold is 79. This is the number of protons in the nucleus of an atom, equal to the number of electrons orbiting the nucleus. The atomic mass - the total mass of protons and neutrons (atomic nucleus) - of gold is 196.9665 amu. (atomic mass units). Natural gold exists in the form of the chemically stable isotope 197 Au. All others are unstable and are possible only in a nuclear reactor.

Formula

Gold does not have its own chemical formula, since it exists in the form of monatomic molecules. The electronic configuration of the Au atom is written as 4f14 5d10 6s1 and denotes the exact distribution of electrons among the orbitals.

Interaction with acids

Due to its inertness (not absolute, but significant), gold does not dissolve in acids. This allows them to be used for refining (chemical purification of an element from impurities): the alloy is treated with an acid, such as nitric acid, and thus gets rid of the alloy.

But there are exceptions. Pure gold is dissolved by acids:

• selenium;
• cyanide and its salts (cyanides);
• nitrogen mixed with hydrochloric water (regia vodka).

Oxidation states and relationships with halogens

Under natural conditions, Au does not oxidize under the influence of oxygen - this is one of the properties that makes the element precious. When heated, gold reacts with halogens (elements of group XVII): iodine, fluorine, bromine and chlorine, forming iodide, fluoride, bromide and chloride, respectively.

Standard oxidation states are 1 and 3. Fluoride with an oxidation state of +5 has been isolated in laboratory conditions.

Measures of gold purity

States control the circulation of precious metals. A century ago, almost every country had its own testing system, but now most have been brought to a common denominator.

British carat system

In the carat system (USA, Canada, Switzerland), the number 24 is considered 100%. The mark “18 K” indicates that the jewelry consists of 75% of precious metal, and 25% of something else - for example, copper and palladium .

Metric system

In Russia, the CIS, and Germany, the number on the stamp is the number of ppm (thousandths) of gold in the alloy. 500 ‰ - sample 500, 375 ‰ -375. Only the 1000 sample does not exist - instead there is 999.9. It contains a microscopic amount of impurities and is conventionally considered pure.

Spool system

The spool sampling system operated in the Russian Empire, the RSFSR and the USSR in 1798–1927. It is based on the Russian pound, equal to 96 spools, similar to the carat mathematically, but divides the whole not into 24, but into 96 shares.

Sample correspondence table

Let's look at the three systems in comparison. There is also a lot sample - it essentially repeats the carat sample, but takes 16 units (lot) for one hundred percent. The lot hallmark was used to hallmark silver in Europe before the introduction of the metric system and has no relation to gold.

Alloys with other metals

In industry they use silver, platinum, palladium, nickel and other metals. The ligature changes the properties of the alloy. Platinum and palladium give it a white color, zinc and cadmium lower the melting point (but zinc makes the alloy brittle, and cadmium does not), copper colors it red and makes it harder.

Application

It is impossible to imagine without gold:

• jewelry making;
• information Technology;
• petrochemical production;
• production of measuring instruments;
• electronics and microelectronics;
• pharmacology;
• nuclear research.

Until now, gold has not lost its original purpose - it is used to save and increase funds.

How to spot a fake

To make money by passing off products made from base alloys as valuable, scammers resort to tricks: burning silver on fire, combining copper with zinc and tin. Pay attention to:

• Brand - it must meet the standard.
• Price - if it is incredibly low, this is an alarming sign.
• Country of origin - check the decoration again if it is Turkey, China or the UAE.

There are tips to try something on your teeth in front of the seller or test it chemically by dropping iodine on it. These are effective methods for determining the authenticity of high standards, but they are not always acceptable in society. If the seller makes you doubt so much that you are ready to bite his goods, you should refuse the purchase.

Conclusion

Do not put gold in mercury or spill hydrocyanic acid on it - this will make it last longer. Also, subscribe to my articles and share them with your friends!