Silver (Ag, 47th element of the periodic table) is a soft metal with a white sheen that lends itself to a high degree of polishing. Along with copper and gold, it is used for minting coins. Silver is considered a noble metal, that is, one that does not lend itself to corrosion. It is the best conductor of heat and electricity. In nature, the Ag element is both in free form and in the composition of compounds, and they learned to extract it in ancient times.
Silver was associated with the moon and female nature, and gold was associated with the sun and a masculine character. In addition, given its attractive white color, it symbolized purity.
Due to the fact that silver belongs to the platinum group, it is considered a precious metal and is often sold as an investment product. The element and its alloys are used in the manufacture of coins, jewelry, dishes, mirrors, printed circuit boards and electronics. Silver nitrates and halides are appreciated in the photograph. AgCl chloride is used to bond glass products and in the manufacture of electrodes to test the acidity of solutions. AgO oxide is used in watch batteries, and AgCNO fulminate is explosive. Elemental silver is non-toxic, but most of its salts in relatively high concentrations are dangerous. In small quantities, some metal compounds have been successfully used to prevent infections.
Natural prevalence and extraction
This chemical element is common in nuggets and in various ores, such as argentite (silver sulfide) Ag 2 S and AgCl chloride. It can also be found in compounds with arsenic or antimony. The main sources of metal are copper, copper-nickel, gold-bearing, lead and lead-zinc ores mined in Canada, Mexico, Peru, Australia and the United States.
The largest silver producer in the world is Mexico. According to the Minister of Economy of this country, in 2000, 80.12 million troy ounces (2492 tons) of this metal were produced in the country, which is about 15% of the annual world production.
Silver is obtained by electrolytic purification of copper. Pure metal of commercial quality has a 99.9% sample. In addition, 99.999 percent purity can be achieved.
Etymology and History
In Latin, silver is called argentum. It is easy to guess which chemical element has the designation Ag.
Silver has been known since ancient times. Slag dumps found in Asia Minor and on the islands of the Aegean Sea indicate that it was separated from lead already in the 4th millennium BC. e. Historically, silver has been used to make jewelry and utensils. In addition, it was used in trade and was the basis of many monetary systems. Its value as a precious metal has long been considered second after gold. And in ancient Egypt and medieval Europe, it was often valued higher.
In the Bible, silver is already mentioned in Genesis. According to the New Testament, Judas Iscariot received a fee of 30 pieces of silver from religious leaders in Jerusalem to betray the Romans to Jesus Christ.
Alchemists associated this metal with the moon, the sea and various moon goddesses, and even called it “moon”. One of the alchemical symbols of this chemical element is a crescent with a concave part on the left.
Metallic mercury was once considered a type of silver, although these substances are not chemically bonded. The Latin name for mercury, Hydrargyrum, literally means "watery silver."
Being in nature
Silver is widespread in nature, but compared to other metals, its total content is quite small. The earth's crust contains 0.05 parts Ag per million. Almost all sulfides of lead, copper and zinc contain a certain amount of silver. Silver-containing ores may contain up to 10% of this metal.
Unlike gold, silver is present in many natural minerals. For commercial use, the most important are compounds such as tetrahedrite and argentite (silver sulfide, Ag 2 S), which is usually associated with other sulfides of lead, copper and some other sulfides, as well as antimony. Silver is usually found in lead and copper ores, cobalt arsenide, it accompanies gold. It is mainly obtained as a by-product of the mining and processing of other metals. But commercially important deposits of natural (chemically free or unbound) silver have also been found.
Since most ores containing silver include lead, copper, zinc, or a combination thereof, it is a by-product of their production. Pure metal is recovered from the crude fraction by smelting, annealing or electrolysis.
Interesting Facts
Europeans found a huge amount of silver in the New World, for example, in Zacatecas in Mexico and Potosi in Bolivia. Conquistador Francisco Pizarro is said to have horses for them, there was so much metal. In Peru, on the other hand, there was a relative lack of iron. At the same time, silver was an extremely valuable metal in other places. This made it a global commodity, caused inflation in Europe and contributed to the rise of the Spanish Empire. The rise and fall in the value of silver has affected the global market.
In honor of silver, the river Rio de la Plata is named. In addition, Argentina got its name from the Latin name of this valuable metal.
The search for silver and related metals (in particular, lead) in galenic ore, in which it is most often found, contributed to the settlement of western North America. The famous “silver rush” occurred in Colorado, Nevada, California, Ontario, and the Kootenay District of British Columbia. The largest metal deposits in the United States were discovered in Virginia (Nevada) in 1859.
Characteristics
In the periodic table, silver belongs to the group of transition metals in the V period, and is located between palladium and cadmium. In addition, it is an element of group 11 with atomic number 47 located between copper and gold. Therefore, its physical and chemical characteristics are average values of the characteristics of these metals. The melting point of Ag is 960.8 ° C, the boiling point is 2212 ° C, and the specific gravity is 10.5 g / cm 3 .
Silver is very ductile and malleable, slightly heavier than gold. It is stable in clean air and water, but darkens when exposed to ozone, hydrogen sulfide, or air containing sulfur. The structure of the Ag lattice is face-centered cubic with a single 5s displaced electron.
Silver has the highest electrical conductivity of all metals - it is even higher than that of copper. However, its higher cost and tarnishing prevented its use in electrical circuits instead of copper. Pure silver has the highest thermal conductivity, the whitest color, the highest optical reflectivity (with the exception of poor ultraviolet light reflection) and low contact strength of all metals.
In combination with other elements, its most common oxidation state is +1. For example, in AgNO 3 nitrate and AgCl chloride. In some compounds, such as AgF 2 fluoride, its valency is 2. The Ag element forms several compounds, such as Ag 2 (SO 5 ) 3 persulfate, in which its oxidation state is +3. Chloride and other silver halides are photosensitive and are known for their effects on light.
Oxygen, in comparison with other gases present in the air, dissolves relatively easily in silver. Attempts have been made to make of it membranes with a thickness of only a few layers of atoms, which can be used to separate pure oxygen from the air.
Isotopes
Silver isotopes in atomic weight range from 93.943 ( 94 Ag) to 123.929 ( 124 Ag) units of atomic mass. In nature, there are 2 stable isotopes of element number 47: Ag-107 and Ag-109. At the same time, the first of them is more widespread (51.839% of the natural content). In addition, 28 radioisotopes have been described, of which 105 Ag (the most stable) has a half-life of 41.29 days, 111 Ag - 7.45 days, and 112 Ag - 3.13 hours.
The half-life of all other radioactive isotopes does not exceed an hour, and in most of them - less than 3 minutes. Silver also has numerous meta states, of which the most stable are 128m Ag (418 years), 110m Ag (249.79 days) and 107m Ag (8.28 days).
The main type of decay to the most common stable 107 Ag isotope is electron capture, and after that - beta decay. The main decay products of up to 107 Ag are considered to be isotopes of palladium (element 46), and after that - isotopes of cadmium (element 48).
Application
Silver (and the platinum group) is used as a precious metal. Its cost however has undergone significant changes. Silver salts, especially nitrates and halides, are widely used in photography. Below are some other uses for silver and its compounds.
Some electrical and electronic products require excellent conductivity of this element. For example, printed circuit boards are made using silver inks, and silver electric contacts are used in computer keyboards. High voltage contacts are made from an alloy of silver with cadmium oxide, since it is able to minimize the electric arc.
In mirrors that require increased reflectivity of visible light, it is used as a reflective material. Conventional mirrors use aluminum.
Silver began to be used as money from 700 BC. e. Lydians in the form of electrum - native glory with gold. Later they learned to clean it and used it in its pure form. The words “silver” and “money” are the same in at least 14 languages.
Plasticity, non-toxicity and beauty of Ag are the characteristics due to which the metal is used in dental alloys from which dental crowns and prostheses are made.
The beauty of metal is the reason for its use in jewelry manufacturing. They are traditionally made from sterling silver (an alloy consisting of 92.5% silver and 7.5% copper). Initially, the British currency pound corresponded to 1 troy pound sterling.
Silver is also used in sports awards given for second place.
The catalytic properties of the Ag element make it ideal for use as a catalyst in oxidation reactions. Examples include the preparation of formaldehyde from methanol and air using a silver sieve or crystallites containing at least 99.95% of this metal. In addition, silver (on a suitable support) is probably the only catalyst that is currently available for converting ethylene to ethylene oxide. The latter can be hydrolyzed to ethylene glycol, which is used in an important industrial reaction to produce polyesters.
The Ag element is used in solders, electrical contacts, and high-power silver-zinc and cadmium batteries. Silver fulminate is a powerful explosive.
Chloride can be made transparent and used as a cement for glass. Compound with chlorine is also widely used to determine acidity and conduct potentiometric measurements.
Silver iodide is sprayed in the air to cause rain. Oxide is used as a positive electrode (cathode) in watch batteries. Colloidal silver is an antibacterial agent used in alternative medicine. However, it causes the infamous argyria.
Until the late 1990s, nitrate (liquid) was a standard antibacterial agent for treating severe burns, but it was replaced by silver sulfadiazine ointment. In addition to these drugs, silver-coated dressings are used to reduce pain and allow treatment at home.
In India, some products and pastries are decorated with thin silver foil.
Use in medicine
Hippocrates, the father of modern medicine, wrote that this chemical element has useful healing properties. The Phoenicians stored water, wine and vinegar in silver bottles to prevent their spoilage. Back in the early 1900s, coins from the “lunar metal” were put in bottles of milk, believing that this prolonged its freshness. Before antibiotics, silver compounds were successfully used to fight infections, for example, during the First World War.
With the advent of modern antibiotics, the widespread use of metal in medicine has gone out of fashion. Recently, however, there has been an increased interest in silver as a broad-spectrum antimicrobial agent. It is used with alginate, a natural biopolymer derived from algae. A number of drugs have been developed to prevent infections in the care of wounds, especially those resulting from a burn.
Precautions
Silver does not perform any natural biological function in humans, and the possible health effects of its use are a matter of debate. The Ag metal itself is not toxic, but most of its salts are dangerous, and some are carcinogenic.
Silver (especially colloidal) and its compounds can penetrate the circulatory system and are deposited in various tissues of the body, which leads to a condition called argyria. It causes pigmentation of the skin, eyes and mucous membranes. Although this condition does not harm human health, it usually does not go away. Argyria is rare, and its mild forms are sometimes mistaken for cyanosis.
Ions and silver compounds have a toxic effect on some bacteria, viruses, algae and fungi, like heavy metals such as lead or mercury. However, for humans they are not as dangerous as lead and mercury.
Alternative medicine
Today, various silver compounds or devices for preparing its solutions are sold as agents for treating a wide range of diseases. Despite the fact that in most cases they are harmless, some people resorting to such methods use too much of this metal and within a few months or years they develop argyria. In recent years, several cases of diseases associated with the use of large doses of silver, including one case of coma, have been recorded in the medical literature. Therefore, doctors strongly recommend reporting self-medication with this metal.
Superstition
The mystical connection with the moon, the aesthetic qualities and the fact that silver symbolizes purity are the reasons that in European folklore it was traditionally considered an antidote to various ailments and fictional monsters. It is noteworthy that with its help they fought with vampires and the living dead. It was believed that a werewolf in his bestial form could only kill a weapon or a bullet of silver. According to East European folklore, silver bullets were an effective remedy against vampires. These beliefs gave rise to a term that is used to describe drugs designed to treat or eliminate a wide range of diseases.