What is arsenic? Definition, formula, properties. Mendeleev's periodic table of elements - arsenic Position of the element in the periodic table arsenic

Arsenic (the name comes from the word mouse, used to bait mice) is the thirty-third element of the periodic table. Refers to semimetals. When combined with an acid, it does not form salts, being an acid-forming substance. Can form allotropic modifications. Arsenic has three currently known crystal lattice structures. Yellow arsenic exhibits the properties of a typical non-metal, amorphous arsenic is black, and the most stable metallic arsenic is gray. In nature, it is most often found in the form of compounds, less often in a free state. The most common are compounds of arsenic with metals (arsenides), such as arsenic iron (arsenopyrite, poisonous pyrite), nickel (kupfernickel, so named because of its similarity to copper ore). Arsenic is a low-active element, insoluble in water, and its compounds are classified as slightly soluble substances. Arsenic oxidation occurs during heating; at room temperature this reaction proceeds very slowly.

All arsenic compounds are very strong toxins that have a negative effect not only on the gastrointestinal tract, but also on the nervous system. History knows many sensational cases of poisoning with arsenic and its derivatives. Arsenic compounds were used as poison not only in medieval France, they were known even in ancient Rome and Greece. The popularity of arsenic as a potent poison is explained by the fact that it is almost impossible to detect it in food; it has neither smell nor taste. When heated, it turns into arsenic oxide. Diagnosing arsenic poisoning is quite difficult, since it has similar symptoms to various diseases. Most often, arsenic poisoning is confused with cholera.

Where is arsenic used?

Despite their toxicity, arsenic derivatives are used not only for baiting mice and rats. Since pure arsenic has high electrical conductivity, it is used as a dopant that imparts the required type of conductivity to semiconductors such as germanium and silicon. In non-ferrous metallurgy, arsenic is used as an additive, which gives alloys strength, hardness and corrosion resistance in a gaseous environment. In glassmaking, it is added in small quantities to brighten glass; in addition, it is part of the famous “Vienna glass”. Nickelin is used to color glass green. In the tanning industry, arsenic sulfate compounds are used when processing hides to remove hairs. Arsenic is part of varnishes and paints. In the woodworking industry, arsenic is used as an antiseptic. In pyrotechnics, “Greek fire” is made from arsenic sulfide compounds and used in the production of matches. Some arsenic compounds are used as chemical warfare agents. The toxic properties of arsenic are used in dental practice to kill dental pulp. In medicine, arsenic preparations are used as a medicine that increases the overall tone of the body, to stimulate an increase in the number of red blood cells. Arsenic has an inhibitory effect on the formation of leukocytes, so it is used in the treatment of some forms of leukemia. A huge number of medical preparations are known that are based on arsenic, but recently they have been gradually replaced by less toxic drugs.

Despite its toxicity, arsenic is one of the most essential elements. When working with its connections, you must adhere to safety rules, which will help avoid undesirable consequences.

Arsenic is a chemical element of the nitrogen group (group 15 of the periodic table). This is a gray, metallic, brittle substance (α-arsenic) with a rhombohedral crystal lattice. When heated to 600°C, As sublimates. When the vapor is cooled, a new modification appears - yellow arsenic. Above 270°C, all forms of As transform into black arsenic.

History of discovery

What arsenic was was known long before it was recognized as a chemical element. In the 4th century. BC e. Aristotle mentioned a substance called sandarac, which is now believed to have been realgar, or arsenic sulfide. And in the 1st century AD. e. the writers Pliny the Elder and Pedanius Dioscorides described orpiment - the dye As 2 S 3. In the 11th century n. e. There were three varieties of “arsenic”: white (As 4 O 6), yellow (As 2 S 3) and red (As 4 S 4). The element itself was probably first isolated in the 13th century by Albertus Magnus, who noted the appearance of a metal-like substance when arsenicum, another name for As 2 S 3, was heated with soap. But there is no certainty that this natural scientist obtained pure arsenic. The first authentic evidence of pure isolation dates back to 1649. German pharmacist Johann Schröder prepared arsenic by heating its oxide in the presence of coal. Later, Nicolas Lemery, a French physician and chemist, observed the formation of this chemical element by heating a mixture of its oxide, soap and potash. By the beginning of the 18th century, arsenic was already known as a unique semimetal.

Prevalence

In the earth's crust, the concentration of arsenic is low and amounts to 1.5 ppm. It is found in soil and minerals and can be released into the air, water and soil through wind and water erosion. In addition, the element enters the atmosphere from other sources. As a result of volcanic eruptions, about 3 thousand tons of arsenic are released into the air per year, microorganisms produce 20 thousand tons of volatile methylarsine per year, and as a result of the combustion of fossil fuels, 80 thousand tons are released over the same period.

Despite the fact that As is a deadly poison, it is an important component of the diet of some animals and, possibly, humans, although the required dose does not exceed 0.01 mg/day.

Arsenic is extremely difficult to convert into a water-soluble or volatile state. The fact that it is quite mobile means that large concentrations of the substance cannot appear in any one place. On the one hand, this is a good thing, but on the other hand, the ease with which it spreads is why arsenic contamination is becoming a bigger problem. Due to human activity, mainly through mining and smelting, the normally immobile chemical element migrates and can now be found in places other than its natural concentration.

The amount of arsenic in the earth's crust is about 5 g per ton. In space, its concentration is estimated to be 4 atoms per million silicon atoms. This element is widespread. A small amount of it is present in the native state. As a rule, arsenic formations with a purity of 90-98% are found together with metals such as antimony and silver. Most of it, however, is included in more than 150 different minerals - sulfides, arsenides, sulfoarsenides and arsenites. Arsenopyrite FeAsS is one of the most common As-containing minerals. Other common arsenic compounds are the minerals realgar As 4 S 4, orpiment As 2 S 3, lellingite FeAs 2 and enargite Cu 3 AsS 4. Arsenic oxide is also common. Most of this substance is a by-product of the smelting of copper, lead, cobalt and gold ores.

In nature, there is only one stable isotope of arsenic - 75 As. Among the artificial radioactive isotopes, 76 As with a half-life of 26.4 hours stands out. Arsenic-72, -74 and -76 are used in medical diagnostics.

Industrial production and application

Metallic arsenic is obtained by heating arsenopyrite to 650-700 °C without air access. If arsenopyrite and other metal ores are heated with oxygen, then As easily combines with it, forming easily sublimated As 4 O 6, also known as “white arsenic”. The oxide vapor is collected and condensed, and later purified by repeated sublimation. Most As is produced by its reduction with carbon from white arsenic thus obtained.

Global consumption of arsenic metal is relatively small - only a few hundred tons per year. Most of what is consumed comes from Sweden. It is used in metallurgy due to its metalloid properties. About 1% arsenic is used in the production of lead shot as it improves the roundness of the molten drop. The properties of lead-based bearing alloys improve both thermally and mechanically when they contain about 3% arsenic. The presence of small amounts of this chemical element in lead alloys hardens them for use in batteries and cable armor. Small arsenic impurities increase the corrosion resistance and thermal properties of copper and brass. In its pure form, the chemical elemental As is used for bronze coating and in pyrotechnics. Highly purified arsenic has applications in semiconductor technology, where it is used with silicon and germanium, and in the form of gallium arsenide (GaAs) in diodes, lasers and transistors.

As connections

Since the valency of arsenic is 3 and 5, and it has a range of oxidation states from -3 to +5, the element can form different types of compounds. Its most important commercially important forms are As 4 O 6 and As 2 O 5 . Arsenic oxide, commonly known as white arsenic, is a byproduct of roasting ores of copper, lead and some other metals, as well as arsenopyrite and sulfide ores. It is the starting material for most other compounds. It is also used in pesticides, as a decolorizing agent in glass production, and as a preservative for leathers. Arsenic pentoxide is formed when white arsenic is exposed to an oxidizing agent (such as nitric acid). It is the main ingredient in insecticides, herbicides and metal adhesives.

Arsine (AsH 3), a colorless poisonous gas composed of arsenic and hydrogen, is another known substance. The substance, also called arsenic hydrogen, is obtained by hydrolysis of metal arsenides and reduction of metals from arsenic compounds in acid solutions. It has found use as a dopant in semiconductors and as a chemical warfare agent. In agriculture, arsenic acid (H 3 AsO 4), lead arsenate (PbHAsO 4) and calcium arsenate [Ca 3 (AsO 4) 2], which are used for soil sterilization and pest control, are of great importance.

Arsenic is a chemical element that forms many organic compounds. Cacodyne (CH 3) 2 As−As(CH 3) 2, for example, is used in the preparation of the widely used desiccant (drying agent) cacodylic acid. Complex organic compounds of the element are used in the treatment of certain diseases, for example, amoebic dysentery caused by microorganisms.

Physical properties

What is arsenic in terms of its physical properties? In its most stable state, it is a brittle, steel-gray solid with low thermal and electrical conductivity. Although some forms of As are metal-like, classifying it as a nonmetal is a more accurate characterization of arsenic. There are other forms of arsenic, but they are not very well studied, especially the yellow metastable form, consisting of As 4 molecules, like white phosphorus P 4 . Arsenic sublimes at a temperature of 613 °C, and in the form of vapor it exists as As 4 molecules, which do not dissociate until a temperature of about 800 °C. Complete dissociation into As 2 molecules occurs at 1700 °C.

Atomic structure and ability to form bonds

The electronic formula of arsenic - 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 3 - resembles nitrogen and phosphorus in that there are five electrons in the outer shell, but it differs from them in having 18 electrons in the penultimate shell instead of two or eight. Adding 10 positive charges to the nucleus while filling the five 3d orbitals often causes an overall decrease in the electron cloud and an increase in the electronegativity of the elements. Arsenic in the periodic table can be compared with other groups that clearly demonstrate this pattern. For example, it is generally accepted that zinc is more electronegative than magnesium, and gallium than aluminum. However, in subsequent groups this difference decreases, and many do not agree that germanium is more electronegative than silicon, despite the abundance of chemical evidence. A similar transition from the 8- to 18-element shell from phosphorus to arsenic may increase electronegativity, but this remains controversial.

The similarity of the outer shell of As and P suggests that they can form 3 per atom in the presence of an additional unbonded electron pair. The oxidation state must therefore be +3 or -3, depending on the relative mutual electronegativity. The structure of arsenic also suggests the possibility of using the outer d-orbital to expand the octet, which allows the element to form 5 bonds. It is realized only when reacting with fluorine. The presence of a free electron pair for the formation of complex compounds (through electron donation) in the As atom is much less pronounced than in phosphorus and nitrogen.

Arsenic is stable in dry air, but turns into a black oxide in humid air. Its vapors burn easily, forming As 2 O 3. What is free arsenic? It is practically unaffected by water, alkalis and non-oxidizing acids, but is oxidized by nitric acid to a state of +5. Halogens and sulfur react with arsenic, and many metals form arsenides.

Analytical chemistry

The substance arsenic can be qualitatively detected in the form of yellow orpiment, which precipitates under the influence of a 25% solution of hydrochloric acid. Traces of As are typically determined by converting it to arsine, which can be detected using the Marsh test. Arsine thermally decomposes to form a black mirror of arsenic inside a narrow tube. According to the Gutzeit method, a sample impregnated with arsine darkens due to the release of mercury.

Toxicological characteristics of arsenic

The toxicity of the element and its derivatives varies widely, from the extremely toxic arsine and its organic derivatives to simply As, which is relatively inert. What arsenic is is evidenced by the use of its organic compounds as chemical warfare agents (lewisite), vesicant and defoliant (Agent Blue based on an aqueous mixture of 5% cacodylic acid and 26% of its sodium salt).

In general, derivatives of this chemical element irritate the skin and cause dermatitis. Protection from inhalation of arsenic-containing dust is also recommended, but most poisoning occurs through ingestion. The maximum permissible concentration of As in dust over an eight-hour working day is 0.5 mg/m 3 . For arsine, the dose is reduced to 0.05 ppm. In addition to the use of compounds of this chemical element as herbicides and pesticides, the use of arsenic in pharmacology made it possible to obtain salvarsan, the first successful drug against syphilis.

Health effects

Arsenic is one of the most toxic elements. Inorganic compounds of this chemical occur naturally in small quantities. People can be exposed to arsenic through food, water, and air. Exposure may also occur through skin contact with contaminated soil or water.

People who work with it, live in homes built from wood treated with it, and on agricultural lands where pesticides have been used in the past are also susceptible to exposure.

Inorganic arsenic can cause a variety of health effects in humans, such as stomach and intestinal irritation, decreased production of red and white blood cells, skin changes, and lung irritation. It is suspected that ingesting significant amounts of this substance may increase the chances of developing cancer, especially cancer of the skin, lungs, liver and lymphatic system.

Very high concentrations of inorganic arsenic cause infertility and miscarriages in women, dermatitis, decreased body resistance to infections, heart problems and brain damage. In addition, this chemical element can damage DNA.

The lethal dose of white arsenic is 100 mg.

Organic compounds of the element do not cause cancer or damage to the genetic code, but high doses can harm human health, for example, cause nervous disorders or abdominal pain.

Properties As

The main chemical and physical properties of arsenic are as follows:

• Atomic number is 33.
• Atomic weight - 74.9216.
• The melting point of the gray form is 814 °C at a pressure of 36 atmospheres.
• The density of the gray form is 5.73 g/cm 3 at 14 °C.
• The density of the yellow form is 2.03 g/cm 3 at 18 °C.
• The electronic formula of arsenic is 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 3.
• Oxidation states - -3, +3, +5.
• The valency of arsenic is 3.5.

Arsenic is a chemical element of group 5 of the 4th period of the periodic table with atomic number 33. It is a brittle semi-metal of steel color with a greenish tint. Today we will take a closer look at what arsenic is and get acquainted with the basic properties of this element.

general characteristics

The uniqueness of arsenic lies in the fact that it is found literally everywhere - in rocks, water, minerals, soil, flora and fauna. Therefore, it is often called nothing less than the omnipresent element. Arsenic is distributed unhindered throughout all geographic regions of planet Earth. The reason for this is the volatility and solubility of its compounds.

The name of the element is associated with its use for the extermination of rodents. The Latin word Arsenicum (arsenic formula in the periodic table is As) is derived from the Greek Arsen, meaning “strong” or “powerful.”

The body of the average adult contains about 15 mg of this element. It is mainly concentrated in the small intestine, liver, lungs and epithelium. Absorption of the substance is carried out by the stomach and intestines. Antagonists of arsenic are sulfur, phosphorus, selenium, some amino acids, as well as vitamins E and C. The element itself impairs the absorption of zinc, selenium, as well as vitamins A, C, B9 and E.

Like many other substances, arsenic can be both a poison and a medicine, it all depends on the dose.

Among the useful functions of such an element as arsenic are:

1. Stimulating the absorption of nitrogen and phosphorus.
2. Improvement of hematopoiesis.
3. Interaction with cysteine, proteins and lipoic acid.
4. Weakening of oxidative processes.

The daily requirement for arsenic for an adult is from 30 to 100 mcg.

Historical reference

One of the stages of human development is called “bronze”, since during this period people replaced stone weapons with bronze ones. This metal is an alloy of tin and copper. Once, when smelting bronze, craftsmen accidentally used weathering products of the copper-arsenic sulfide mineral instead of copper ore. The resulting alloy was easy to cast and excellent forging. In those days, no one yet knew what arsenic was, but deposits of its minerals were deliberately sought for the production of high-quality bronze. Over time, this technology was abandoned, apparently due to the fact that poisoning often occurred with its use.

In Ancient China they used a hard mineral called realgar (As 4 S 4). It was used for stone carving. Since under the influence of temperature and light realgar turned into another substance - As 2 S 3, it was also soon abandoned.

In the 1st century BC, the Roman scientist Pliny the Elder, along with the botanist and physician Dioscorides, described the arsenic mineral called orpiment. Its name is translated from Latin as “golden paint”. The substance was used as a yellow dye.

In the Middle Ages, alchemists classified three forms of the element: yellow (As 2 S 3 sulfide), red (As 4 S 4 sulfide) and white (As 2 O 3 oxide). In the 13th century, by heating yellow arsenic with soap, alchemists obtained a metal-like substance. Most likely, it was the first example of a pure element obtained artificially.

What arsenic is in its pure form was discovered at the beginning of the 17th century. This happened when Johann Schröder, reducing the oxide with charcoal, isolated this element. A few years later, the French chemist Nicolas Lemery managed to obtain the substance by heating its oxide in a mixture with soap and potash. In the next century, arsenic was already well known in its semimetal status.

Chemical properties

In the periodic table of Mendeleev, the chemical element arsenic is located in the fifth group and belongs to the nitrogen family. Under natural conditions, it is the only stable nuclide. More than ten radioactive isotopes of the substance are produced artificially. Their half-life range is quite wide - from 2-3 minutes to several months.

Although arsenic is sometimes called a metal, it is more likely to be a non-metal. In combination with acids, it does not form salts, but is itself an acid-forming substance. This is why the element is identified as a semimetal.

Arsenic, like phosphorus, can be found in various allotropic configurations. One of them, gray arsenic, is a brittle substance that has a metallic sheen when broken. The electrical conductivity of this semimetal is 17 times lower than that of copper, but 3.6 times higher than that of mercury. As the temperature increases, it decreases, which is typical for typical metals.

By rapidly cooling arsenic vapor to the temperature of liquid nitrogen (-196 °C), a soft yellowish substance resembling yellow phosphorus can be obtained. When heated and exposed to ultraviolet light, yellow arsenic instantly turns gray. The reaction is accompanied by the release of heat. When vapors condense in an inert atmosphere, another form of matter is formed - amorphous. If arsenic vapor is precipitated, a mirror film appears on the glass.

The outer electron shell of this substance has the same structure as phosphorus and nitrogen. Like phosphorus, arsenic forms three covalent bonds. In dry air it has a stable shape, and with increasing humidity it becomes dull and becomes covered with a black oxide film. When the vapor is ignited, the substances burn with a blue flame.

Since arsenic is inert, it is not affected by water, alkalis and acids, which do not have oxidizing properties. When a substance comes into contact with dilute nitric acid, orthoarsenic acid is formed, and with concentrated acid, orthoarsenic acid is formed. Arsenic also reacts with sulfur, forming sulfides of different compositions.

Being in nature

Under natural conditions, a chemical element such as arsenic is often found in compounds with copper, nickel, cobalt and iron.

The composition of the minerals that the substance forms is due to its semi-metallic properties. To date, more than 200 minerals of this element are known. Since arsenic can exist in negative and positive oxidation states, it easily interacts with many other substances. During positive oxidation of arsenic, it functions as a metal (in sulfides), and during negative oxidation, it functions as a nonmetal (in arsenides). Minerals containing this element have a rather complex composition. In a crystal lattice, a semimetal can replace atoms of sulfur, antimony and metals.

From a compositional point of view, many metal compounds with arsenic are more likely to belong not to arsenides, but to intermetallic compounds. Some of them are distinguished by variable content of the main element. Arsenides can simultaneously contain several metals, the atoms of which can replace each other at close ion radii. All minerals classified as arsenides have a metallic luster, are opaque, heavy and durable. Among the natural arsenides (there are about 25 in total) the following minerals can be noted: skutterudite, rammelsbreggite, nickelin, lellingrite, clinosafflorite and others.

Interesting from a chemical point of view are those minerals in which arsenic is present simultaneously with sulfur and plays the role of a metal. They have a very complex structure.

Natural salts of arsenic acid (arsenates) can have different colors: erythritol - cobalt; simplesite, annabergite and scoride are green, and rooseveltite, kettigite and gernessite are colorless.

In terms of its chemical properties, arsenic is quite inert, so it can be found in its native state in the form of fused cubes and needles. The content of impurities in the nugget does not exceed 15%.

In soil, the arsenic content ranges from 0.1-40 mg/kg. In areas of volcanoes and places where arsenic ore occurs, this figure can reach up to 8 g/kg. Plants in such places die and animals get sick. A similar problem is typical for steppes and deserts, where the element is not washed out from the soil. Clay rocks are considered enriched, since they contain four times more arsenic substances than ordinary rocks.

When a pure substance is converted into a volatile compound through the process of biomethylation, it can be carried out of the soil not only by water, but also by wind. In normal areas, the concentration of arsenic in the air averages 0.01 μg/m 3 . In industrial areas where factories and power plants operate, this figure can reach 1 μg/m3.

Mineral water may contain a moderate amount of arsenic substances. In medicinal mineral waters, according to generally accepted standards, the concentration of arsenic should not exceed 70 µg/l. It is worth noting here that even at higher rates, poisoning can only occur with regular consumption of such water.

In natural waters, the element can be found in various forms and compounds. Trivalent arsenic, for example, is much more toxic than pentavalent arsenic.

Obtaining arsenic

The element is obtained as a by-product of the processing of lead, zinc, copper and cobalt ores, as well as during gold mining. In some polymetallic ores, the arsenic content can reach up to 12%. When they are heated to 700 °C, sublimation occurs - the transition of a substance from a solid to a gaseous state, bypassing the liquid state. An important condition for this process to occur is the absence of air. When arsenic ores are heated in air, a volatile oxide is formed, called “white arsenic.” By subjecting it to condensation with coal, pure arsenic is recovered.

The formula for getting an element is as follows:

• 2As 2 S 3 +9O 2 =6SO 2 +2As 2 O 3;
• As 2 O 3 +3C=2As+3CO.

Arsenic mining is a hazardous industry. Paradoxical is the fact that the greatest pollution of the environment by this element occurs not near the enterprises that produce it, but near power plants and non-ferrous metallurgy plants.

Another paradox is that the volume of production of metallic arsenic exceeds the need for it. This is a very rare occurrence in the metal mining industry. Excess arsenic must be disposed of by burying metal containers in old mines.

The largest deposits of arsenic ores are concentrated in the following countries:

1. Copper-arsenic - USA, Georgia, Japan, Sweden, Norway and Central Asian states.
2. Gold-arsenic - France and USA.
3. Arsenic-cobalt - Canada and New Zealand.
4. Arsenic-tin - England and Bolivia.

Definition

Laboratory determination of arsenic is carried out by precipitation of yellow sulfides from hydrochloric acid solutions. Traces of the element are determined using the Gutzeit method or the Marsh reaction. Over the last half century, all sorts of sensitive analysis techniques have been created that can detect even very small amounts of this substance.

Some arsenic compounds are analyzed using the selective hybrid method. It involves the reduction of the test substance into the volatile element arsine, which is then frozen in a container cooled with liquid nitrogen. Subsequently, when the contents of the container are slowly heated, the various arsines begin to evaporate separately from each other.

Industrial use

Almost 98% of mined arsenic is not used in its pure form. Its compounds are widely used in various industries. Hundreds of tons of arsenic are mined and processed annually. It is added to bearing alloys to improve their quality, used to increase the hardness of cables and lead batteries, and is also used in the production of semiconductor devices along with germanium or silicon. And these are just the most ambitious areas.

As a dopant, arsenic imparts conductivity to some “classical” semiconductors. Its addition to lead significantly increases the strength of the metal, and to copper - fluidity, hardness and corrosion resistance. Arsenic is also sometimes added to some grades of bronzes, brasses, babbitts and type alloys. However, metallurgists often try to avoid using this substance, since it is unsafe for health. For some metals, large amounts of arsenic are also harmful because they degrade the properties of the original material.

Arsenic oxide has found use in glass making as a glass brightener. It was used in this direction by ancient glassblowers. Arsenic compounds are a strong antiseptic, so they are used to preserve furs, stuffed animals and skins, and also to create antifouling paints for water transport and impregnation for wood.

Due to the biological activity of some arsenic derivatives, the substance is used in the production of plant growth stimulants, as well as medicines, including anthelmintics for livestock. Products containing this element are used to control weeds, rodents and insects. Previously, when people did not think about whether arsenic could be used for food production, the element had wider uses in agriculture. However, after its toxic properties were discovered, a replacement had to be found.

Important areas of application of this element are: the production of microcircuits, fiber optics, semiconductors, film electronics, as well as the growth of microcrystals for lasers. For these purposes, gaseous arsines are used. And the production of lasers, diodes and transistors is not complete without gallium and indium arsenides.

Medicine

In human tissues and organs, the element is presented mainly in the protein fraction, and to a lesser extent in the acid-soluble fraction. It is involved in fermentation, glycolysis and redox reactions, and also ensures the breakdown of complex carbohydrates. In biochemistry, compounds of this substance are used as specific enzyme inhibitors, which are necessary for the study of metabolic reactions. Arsenic is necessary for the human body as a trace element.

The use of the element in medicine is less extensive than in production. Its microscopic doses are used to diagnose all kinds of diseases and pathologies, as well as to treat dental diseases.

In dentistry, arsenic is used to remove pulp. A small portion of a paste containing arsenous acid ensures the death of the tooth literally within a day. Thanks to its action, pulp removal is painless and unhindered.

Arsenic is also widely used in the treatment of mild forms of leukemia. It allows you to reduce or even suppress the pathological formation of leukocytes, as well as stimulate red hematopoiesis and the release of red blood cells.

Arsenic is like poison

All compounds of this element are poisonous. Acute arsenic poisoning results in abdominal pain, diarrhea, nausea, and central nervous system depression. The symptoms of intoxication with this substance resemble those of cholera. Therefore, earlier cases of intentional arsenic poisoning were often encountered in judicial practice. For criminal purposes, the element was most often used in the form of trioxide.

Symptoms of intoxication

At first, arsenic poisoning manifests itself as a metallic taste in the mouth, vomiting and abdominal pain. If measures are not taken, convulsions and even paralysis may occur. In the worst case, poisoning can be fatal.

The cause of poisoning can be:

1. Inhalation of dust containing arsenic compounds. Occurs, as a rule, in arsenic production plants where labor safety rules are not followed.
2. Consuming poisoned food or water.
3. Use of certain medications.

First aid

The most widely available and well-known antidote for arsenic intoxication is milk. The casein protein it contains forms insoluble compounds with the toxic substance that cannot be absorbed into the blood.

In case of acute poisoning, to quickly help the victim, he needs to undergo gastric lavage. In hospital settings, hemodialysis is also carried out, aimed at cleansing the kidneys. Among medications, a universal antidote is used - Unithiol. Additionally, antagonist substances can be used: selenium, zinc, sulfur and phosphorus. In the future, the patient is required to be prescribed a complex of amino acids and vitamins.

Arsenic deficiency

Answering the question: “What is arsenic?”, it is worth noting that the human body needs it in small quantities. The element is considered immunotoxic, conditionally essential. It takes part in almost all the most important biochemical processes of the human body. A deficiency of this substance may be indicated by the following signs: a decrease in the concentration of triglycerides in the blood, deterioration in the development and growth of the body.

As a rule, in the absence of serious health problems, there is no need to worry about a lack of arsenic in the diet, since the element is found in almost all products of plant and animal origin. Seafood, cereals, grape wine, juices, and drinking water are especially rich in this substance. Within 24 hours, 34% of consumed arsenic is eliminated from the body.

In case of anemia, the substance is taken to increase appetite, and in case of selenium poisoning, it acts as an effective antidote.

Arsenic compounds (English and French Arsenic, German Arsen) have been known for a very long time. In the III - II millennia BC. e. already knew how to produce copper alloys with 4 - 5% arsenic. Aristotle's student, Theophrastus (IV-III centuries BC), called red arsenic sulfide found in nature as realgar; Pliny calls yellow arsenic sulphide As 2 S 3 orpiment (Auripigmentum) - golden in color, and later it received the name orpiment. The ancient Greek word arsenicon, as well as sandarac, refer mainly to sulfur compounds. In the 1st century Dioscorides described the burning of orpiment and the resulting product - white arsenic (As 2 O 3). In the alchemical period of the development of chemistry, it was considered undeniable that arsenic (Arsenik) has a sulfurous nature, and since sulfur (Sulfur) was revered as the “father of metals,” masculine properties were attributed to arsenic. It is unknown when exactly arsenic metal was first obtained. This discovery is usually attributed to Albert the Great (13th century). Alchemists considered the coloring of copper with the addition of arsenic to a white silver color as the transformation of copper into silver and attributed such a “transmutation” to the powerful power of arsenic. In the Middle Ages and in the first centuries of modern times, the toxic properties of arsenic became known. However, even Dioscorides (Iv.) recommended that asthma patients inhale the vapors of the product obtained by heating realgar with resin. Paracelsus already widely used white arsenic and other arsenic compounds for treatment. Chemists and miners of the 15th - 17th centuries. knew about the ability of arsenic to sublimate and form vaporous products with a specific odor and toxic properties. Vasily Valentin mentions what was well known to metallurgists of the 16th century. blast furnace smoke (Huttenrauch) and its specific smell. The Greek (and Latin) name for arsenic, referring to arsenic sulfides, is derived from the Greek masculine. There are other explanations for the origin of this name, for example from the Arabic arsa paki, meaning “an unfortunate poison penetrating deep into the body”; the Arabs probably borrowed this name from the Greeks. The Russian name arsenic has been known for a long time. It has appeared in literature since the time of Lomonosov, who considered arsenic to be a semimetal. Along with this name in the 18th century. the word arsenic was used, and arsenic was called As 2 O 3. Zakharov (1810) proposed the name arsenic, but it did not catch on. The word arsenic was probably borrowed by Russian artisans from the Turkic peoples. In Azerbaijani, Uzbek, Persian and other eastern languages, arsenic was called margumush (mar - kill, mush - mouse); Russian arsenic, probably a corruption of mouse-poison, or mouse-venom.

DEFINITION

Arsenic- thirty-third element of the Periodic Table. Designation - As from the Latin "arsenicum". Located in the fourth period, VA group. Refers to semimetals. The nuclear charge is 33.

Arsenic occurs in nature mostly in compounds with metals or sulfur and only rarely in a free state. The arsenic content in the earth's crust is 0.0005%.

Arsenic is usually obtained from arsenic pyrite FeAsS.

Atomic and molecular mass of arsenic

Relative molecular weight of the substance(M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.

Since in the free state arsenic exists in the form of monatomic As molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 74.9216.

Allotropy and allotropic modifications of arsenic

Like phosphorus, arsenic exists in several allotropic forms. With rapid cooling of steam (consisting of As 4 molecules), a non-metallic fraction is formed - yellow arsenic (density 2.0 g / cm 3), isomorphic to white phosphorus and, like it, soluble in carbon disulfide. This modification is less stable than white phosphorus, and when exposed to light or low heating it easily transforms into a metallic modification - gray arsenic (Fig. 1). It forms a steel-gray brittle crystalline mass with a metallic sheen when freshly fractured. The density is 5.75 g/cm3. When heated under normal pressure, it sublimates. Has metallic electrical conductivity.

Rice. 1. Gray arsenic. Appearance.

Isotopes of arsenic

It is known that in nature arsenic can be found in the form of the only stable isotope 75 As. The mass number is 75, the nucleus of an atom contains thirty-three protons and forty-two neutrons.

There are about 33 artificial unstable isotopes of arsenic, as well as ten isomeric states of nuclei, among which the longest-lived isotope 73 As with a half-life of 80.3 days.

Arsenic ions

The outer energy level of the arsenic atom has five electrons, which are valence electrons:

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 3 .

As a result of chemical interaction, arsenic gives up its valence electrons, i.e. is their donor, and turns into a positively charged ion:

As 0 -3e → As 3+ ;

As 0 -5e → As 5+ .

Arsenic molecule and atom

In the free state, arsenic exists in the form of monatomic As molecules. Here are some properties characterizing the arsenic atom and molecule:

Examples of problem solving

EXAMPLE 1