The valence of the manganese. Properties of chemical elements

In the fourth period system of the chemical elements number 25 is the metal – manganese, along with the technetium and rhenium side it forms a subgroup of the seventh group. The element is widely distributed in the earth's crust and is part of the different rocks: pyrolusite, braunite, hausmannite. Manganese valence of which can be equal to II, III, IV, VI,VII, forms large number of compounds. This, for example, oxides, acids and salts that play an important role in the metallurgical industry. In our article we will find out their properties, methods of obtaining and application in various industries, in medicine and in everyday life.

Physical characteristics

According to position in the periodic system of chemical elements D. I. Mendeleev, metal belongs to d-elements whose valence are not only the two electrons of the last layer of energy, but also negative particles, located on the third level. As you know, all d-elements exhibit physical and chemical properties typical of metals. Manganese – not the exception. It has a silver-white color, hard and heavy (with a density of 7.44 g/cm³) at a temperature below 727° becomes brittle. The crystal lattice can form four versions: α, β, ϒ and body-centred cubic form. They are all persistent entities in only a certain range of temperatures.

Position in the series of metal activity

Physico-chemical properties of manganese depend not only on its place in the periodic system of chemical elements, but also on its position in a series of metal activity, created by the Russian scientist N. N. Beketov. In this manganese has a standard electrode potential equal to V. -1,179 Element is located between aluminium and zinc. This speaks to the ability of Mn atoms displace hydrogen ions from water solutions of acids in redox processes. The valence of the manganese in such reactions is usually equal to II. The element reacts with dilute solutions of nitrate and chloride acids. Also, the metal participates in the substitution reaction with hot concentrated sulphate acid. In the products is detected by sulfur dioxide and water. In addition to them forms a Sol – manganese sulfate. In it the valence of the metal atom is equal to two. But in cold sulphuric acid, the manganese is not soluble due to the formation on its surface a protective oxide film (passivation of metals).

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Characteristics of the compounds of bivalent manganese

Under the action of acids on natural compounds containing ions of Mn²⁺ or in the process of dissolving a simple substance – the metal in dilute solutions of inorganic acids, the formation of salts of divalent manganese. For example, crystals of manganese chloride is pink in color can be extracted by the action of hydrochloric acid on manganese oxide, the valence of which is equal to IV. In the laboratory, acting on such salts are alkali, you get a white precipitate of the hydroxide Mn(OH)₂. In an open vial in air it is oxidized into a brown substance. Binary compound – oxide of divalent manganese, is a product of the reduction with hydrogen of metallic oxides with oxidation state +4 or +7.

Amphoteric properties manganese dioxide

With increasing valence in the compounds of the metal with oxygen can be traced to the weakening and strengthening of the basic acid properties. Thus, a compound of the formula Mn₂O₃ And the monoxide of manganese, in which the valence of the metal atom is equal to II, have the main character, dioxide – alfaterna, and Mn₂O₇ is the anhydride of manganic acid. In an environment where pH is less than 7, the dioxide behaves as a strong oxidant. In that capacity it is used in galvanic cells and in the industrial production of chlorine from hydrochloric acid. The regenerative capacity of the manganese dioxide in the reaction manifests itself very poorly.

The most Important compounds of hexavalent and pneumococcal of manganese

Fusing the dioxide metal salts – nitrates and carbonates, it is possible to obtain a solid green color. It is highly soluble in water. Evaporating the solution produced a dark green crystalline compound – manganate potassium, the valence of manganese which is equal to VI. In reactions with strong oxidizing agents – fluorine, chlorine, a substance turns into acid salt of manganese – potassium permanganate. Her dark purple crystals familiar, and at home it is called potassium permanganate. Its solution has a raspberry color and in low concentrations is used as a fine dezinfectarea tool for outdoor use. In the course of school chemistry research of redox processes in which potassium permanganate is used as oxidant. Depending on the reaction of the solution (neutral, acidic or alkaline) in the product detected a different connection.

For Example, in an acidic medium in the interaction with the potassium sulfite ions Mn⁺⁷ is restored to Mn⁺², obtained manganese sulfate. In a neutral environment is the loss of brown sludge, and the valence of the manganese in the oxide formed will be equal to IV. In alkaline medium the reaction of sulfite and potassium saltsmanganese acid ends with the appearance in solution of ions of potassium manganate.

Obtaining and use of metal

The Most pure samples of manganese can be obtained in the process of electrolysis of a solution of its sulphate, which is formed during the recovery of pyrolusite, braunite or hausmannite. As we said earlier, the valence of manganese in the compounds included in the composition of ores, equal II. A cheaper method, compared to the energy-intensive electrolysis, can be considered silicothermic process. It lies in the reduction reaction of oxides of manganese and silicon, which is carried out in electric furnaces. However, the purity of the metal produced is lowered. The most popular manganese in the production of alloy steels, containing up to 15 %.

Such alloys are particularly robust and resistant to shock and vibration, therefore they have found application in the production of rails, parts for stone crushing machines and rock drills. If the alloy composition is not only manganese, but also magnesium, it acquires the ability to withstand factors that cause different types of corrosion. Structural alloys – melchiori and neusilber used in shipbuilding, the manufacture of pipes and radiators also contain a small portion of manganese. The electrical composition of the alloys, e.g. manganin, the metal content reaches 12 %, they are characterized by low temperature indicator electrical resistance and are widely used in engineering.