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Degrees of oxidation of arsenic: chemical properties of arsenic

Before considering the degree of oxidation of arsenic, we will reveal its position in the periodic table and the features of the structure. In addition, let's name the basic physical and chemical properties of this chemical element.

Position in the PS

The main degrees of oxidation of arsenic, chemical properties, application - all this can be learned by looking at the location of the element in the periodic system of Mendeleev. Arsenic is located in the fifth group, the main subgroup, is a member of the nitrogen family. It has a relative atomic mass of 74.9216. The main degrees of oxidation of arsenic are related precisely to the group in which it is located in the SS. This element has 33 serial number. The number of energy levels corresponds to the number of the period in which the element is located, it is equal to four.

Consider the arrangement of electrons on each atomic shell. At the first energy level there are only two paired electrons, the second shell is occupied by eight particles: 2s and 6p. At the third level, apart from them, ten d-electrons are located, that is, only 18 particles. The external energy level is a 2s-electron, as well as three unpaired p-electrons. It is the number of valence electrons that determines the possible degrees of oxidation of arsenic.

Pages of History

It is arsenic attributed to the five "alchemical" elements, known from the Middle Ages. An interesting point is the fact that four of them are in the fifth PS group. In those days no one knew how to determine the degree of oxidation of arsenic, but its compounds were successfully used to make medicines, create paints.

After the replacement of the Stone Age by the Bronze Age, people learned to make this alloy with special characteristics. It turns out that it contained up to 7 percent of arsenic and only 3 percent of tin. Scientists believe that the first smelting of bronze instead of malachite, which is green, mistakenly took the green sulfides of copper-arsenic minerals.

The amazing performance of the resulting alloy made it popular among ancient masters. They specifically looked for in nature minerals containing this substance.

The degrees of oxidation of arsenic in compounds of this type are positive, corresponding to its higher valence. To identify sulfides containing arsenic, the mineral is heated. The appearance of a specific garlic smell is a confirmation of the presence of arsenic in the compound. Gradually from the smelting of arsenic bronze refused. Among the reasons for the termination of production, scientists call the constant poisoning of masters during work.

Natural Minerals

In the form of a mineral, the substance we are considering has been known since ancient times. For example, the degree of oxidation of 3 arsenic appears in a compound known in ancient China as "mine dust". Aristotle described the mineral sandarak, which is an arsenic sulphide. Translated from the Latin language, its name sounds like "golden paint". Used it in those distant times as a yellow dye.

In the eleventh century, the alchemists distinguished three different species of this substance. The degrees of oxidation of arsenic in the compounds represented by these species correspond to the group number. White arsenic called it hexavalent oxide, yellow was called sulphide, and red - As4S4 (tetrasulfide tetrashyyyaka).

The white variant was obtained by sublimation of impurities during the roasting of copper ores, which included arsenic. As condensation from the gaseous state, arsenic oxide precipitates as a white deposit. It has been used since ancient times as a means of destroying pests.

In the thirteenth century, Albert the Great received a gaseous substance. He heated yellow arsenic with soap. The substance obtained as a result of the interaction did not confirm the "mystical connection" of the seven metals with the planets. Perhaps, precisely because of the revealed contradiction by the ancient alchemists, arsenic was considered an "illegitimate" element. It was in those early times that his ability to give copper a white color was revealed, which made him to be called a means of "bleaching Venus".

As an individual substance, this chemical element was identified only in the middle of the seventeenth century. German pharmacist Johann Schröder managed to isolate him by conducting a chemical reduction of coal oxides. After a while, Nichola Lemery managed to extract the metal by heating potash, soap, arsenic oxide. In the 18th century, this metal was known as an unusual "semimetal".

At the end of the 18th century, the Swedish chemist KV Scheele obtained arsenic acid, in which the highest degree of oxidation of arsenic is manifested: +5. In the nineteenth century, organic substances that contain arsenic were identified.

Being in nature

The highest and lowest degree of oxidation of arsenic is manifested in its natural compounds. In the Earth's crust, the percentage concentration of this element does not exceed 5 grams per ton. In many minerals it is contained simultaneously with nickel, cobalt, copper, iron.

At present, about two hundred different natural minerals are known, including the chemical element under consideration. Given that they exhibit the highest and lowest degree of oxidation of arsenic, they have a different application. For example, in combination with antimony, arsenic exhibits a negative oxidation state. Given the fact that this metal has low electronegativity, the lowest degree of oxidation of arsenic is -3. This indicator is characteristic for arsenides, as well as for the mineral almontite.

Most of the compounds with arsenic metals, taking into account the specific composition, are intermetallic compounds characterized by the variable composition of this chemical element.

Characteristics of arsenides

Arsenides are characterized by the content of several metals having a similar structure of crystal lattices. These minerals are characterized by metallic shine, they are opaque, have a slight hardness.

As examples of natural arsenides, the following compounds can be considered:

  • Lellingite, similar to pyrite;
  • Nickel, referred to as nickel red pyrite;
  • Langisite;
  • Oreonite;
  • Sperrylite.

This, of course, is not a complete list of such minerals - at the moment there are about twenty-five such compounds. Among the most common in nature can be mentioned arsenopyrite, called arsenic pyrite. It is a product obtained by replacing the sulfur atoms in pyrite with arsenic. Compounds of this type, in which the highest degree of oxidation of arsenic is not manifested, is called sulfosalts.

Their analogs consider cobalt shine, gersdorffite, enargite, and also proustite. The latter is an important silver ore, located in the upper layer of precious veins. The composition of sulfosalts can include noble metals of the platinum group. Among them is the interest of irarsite, as well as the orsit. They contain rare metals used as excellent catalysts in organic and inorganic syntheses.

The maximum degree of oxidation of arsenic is manifested in its natural sulphides. For example, in the orange-yellow dimorphite, which is arsenic sulfide (5). In the thirties of the last century, natural deposits of auripigment were discovered, which included sulfide of arsenic in its composition, in the south of the Verkhoyansk Range. The size of the detected crystals reached 60 centimeters in length, and the weight was estimated at 30 kilograms.

Characteristics of arsenates

Possible degrees of oxidation of arsenic can be considered by the example of salts. Thus, arsenic acid compounds, called arsenates, show the maximum value for this metal: +5. As an example of such compounds, we give erythrin, which has a bright pink color. This salt is called cobalt color, it has the formula Co3 (AsO4) 2 * 8H 2 O. It can also be noted that the brown-red shade is of the form (Ce, La, Nd) ArO 4 .

In the center of Sweden, Langbana iron-manganese quarries were discovered, where about fifty different arsenates were found and characterized. These compounds were formed by the interaction of arsenous acid with manganese hydroxide (2) at low temperatures.

Which arsenates show oxidation states of arsenic? The characteristics of these salts confirm the presence of sulfur in them. Despite the absence of industrial applications, their aesthetic appearance allows them to be used to create mineralogical collections.

An interesting story is kupfernikel, which corresponds to the nickel mineral. Medieval German miners Nickel called the mountain evil spirit, and "fake copper" was called "kupfernickel." The masters revealed the external similarity of copper-red crystals of this mineral with copper ores. They were used in glass making to give the resulting product a green tint. Only in the middle of the eighteenth century the mineralogist Axel Kronstedt succeeded in isolating nickel from this mineral.

Peculiarities of accommodation in nature

Arsenic is characterized by high inertia, so it can be found in a native state. A similar metal in the composition has from two to sixteen percent impurities, mainly they will be silver, iron, cobalt, nickel. In our country, geologists discovered native arsenic in the Amur region, Transbaikalia.

It can be found in rocks, in minerals, and in plants, so it is rightfully often called the ubiquitous element.

What is the maximum and minimum degree of oxidation of arsenic? The highest value corresponds to the number of the group in which this element is located and is +5. This is typical for compounds in which it exhibits reducing properties. More details of the connection of this unique metal will be considered later.

The arsenic is extremely unevenly distributed around the globe. The reason lies in the formation of the lithosphere, as well as in the desorption and sorption processes occurring in sedimentary rocks and soils.

Due to the excellent solubility of this metal in water, it easily migrates. For example, in a humid climate, it is washed out of the soil, followed by movement along with groundwater and rivers.

Physiological action

In significant quantities, arsenic is found in mineral waters. There are certain standards for the content of this metal. If the permissible values are exceeded, a serious threat of harm to the human body arises. In the course of chemical research it was found that arsenic can be contained in various forms in natural water. What should be the oxidation states of arsenic? The properties of the compounds found in water confirm the presence of the metal as an arsenious acid solution.

Arsenic in a living form contains about 6 mg per 1 kilogram. Part of the seaweed can accumulate the above substance in such a degree that it can be dangerous for the human body. Some of their species found in Asian countries are able to multiply in a pure acid solution. They are used as a means of controlling rats. In the brain tissue of a person, as well as in his muscles, there is a sufficient amount of this metal. In addition, it is present in the nail plates, accumulates in the hair.

physical characteristics

Despite the fact that arsenic looks like metal, it has nonmetallic features. For example, it is unable to form salts with sulfuric acid, acting as an acid-forming element. Arsenic can exist in various allotropic modifications, reminiscent of phosphorus. The most stable is gray arsenic, which, when heated, sublimates like iodine.

According to electrical conductivity, this modification is inferior to copper, but exceeds mercury. When cooling arsenic vapors, you can get a soft transparent substance of a yellow shade, similar to yellow phosphorus. During the heating process, it turns into another allotropic modification of this chemical element.

When depositing arsenic vapors on a glass, one can observe the appearance of a mirror film.

Arsenic compounds

The degree of oxidation of arsenic in the higher oxide is +5, that is, it corresponds to its higher valence. But in the sublimation of vapors of a given metal in moist air, a black film of its arsenic anhydride As2O 3 is formed . It is in this form that the oxide of this element exists in the main. This oxide exhibits amphoteric chemical properties.

In the oxidation process, it turns into a higher oxide, where arsenic demonstrates the value of the degree of oxidation +5.

The pure metal is oxidized by dilute nitric acid to the ortho-arsenic acid H 3 AsO 3 , in which it has a valence of 3. In its chemical potential, it is considered to be an acid of medium strength similar to boric acid. Salts are considered arsenites, which show bright reducing properties.

In chloride, the metal has an oxidation state of +3, acting as a typical metallic element. The salt-like arsenides formed during the interaction with the active metals are subjected to aqueous hydrolysis. For example, arsine (AsH 3 ) is a toxic, colorless gas, odorless.

Organometallic compounds

Arsenic is capable of forming various organometallic compounds. For example, at the end of the 18th century, with distillation with arsenic oxide (3) of potassium acetate, a smoking liquid with an unpleasant odor was obtained. The product obtained was called alarsin. In subsequent studies, it was found that it contains arsenic.

In the late nineteenth century, aromatic arsins were synthesized. The reaction was carried out by exposure to a mixture of arsenic trichloride and aryl halide with metallic sodium. Some of these products demonstrated antimicrobial properties. To date, a synthesis of tens of thousands of organochlorine compounds is being carried out.

Application of arsenic

More than half of all extracted metal is used in the form of various compounds. In its pure form it is practically not used. In a small amount, it is introduced into the bearing alloys. Such additives have a positive effect on the hardness of the finished product, so they are in demand in the manufacture of electrical cables and batteries.

Minimal doses of arsenic contribute to increased corrosion resistance, improve the thermal performance of brass and copper. If this element does not contain additional impurities, then it is in demand in the manufacture of semiconductor devices. To create them, arsenic is fused with germanium or silicon.

In addition, it is an excellent alloying additive for making steels. As a valuable nozzle, arsenic is also needed in non-ferrous metallurgy. Even with its low content in the alloy, it is possible to significantly improve the strength of the product being manufactured. Arsenic increases the fluidity of copper during casting, facilitating the process of obtaining wire.

There is also a certain negative impact of this transition metal on production. Its presence in the ore turns the process into harmful production.

Among the various compounds of arsenic, its trivalent oxide is of interest. It is currently used in the glass industry. Salts with an indicator of +5 are in demand as antiseptics. This transition element is one of the most in demand in modern chemical production, as it exhibits dual properties depending on the process environment.

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