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Selenium - what is it? The chemical element is selenium. Application of selenium

What do we know about the selenium? At school chemistry lessons, we were told that selenium is a chemical element, we could solve various chemical equations and observe reactions with its participation. But there are so many elements in Mendeleev's table that it is impossible to cover all the information. Therefore, everything is presented rather briefly.

In this article, you can learn more about the element called "selenium". What is it, what are its properties, where in nature you can find this element and how it is used in the industry. In addition, it is important to know what impact it has on our body.

What is selenium

Selenium (element Selenium) is a chemical element, a sulfur analogue, which belongs to the 16th group (according to the earlier classification - to the 6th) of Mendeleyev's table. The atomic number of the element is 34, and the atomic mass is 78.96. The element exhibits predominantly non-metallic properties. In nature, selenium is a complex consisting of six isotopes, usually accompanied by sulfur. That is, it occurs in the places of sulfur extraction. So, mysterious selenium - what is it and what is it so valuable? It has many useful properties.

History of selenium discovery

This chemical element was discovered by the Swedish chemist and mineralogist Jönns Jakob Berzelius in 1817.

In the scientific literature there is a history of discovery of the mineral, told by the scientist himself.

He says that at that time he, along with another scientist named Johan Gottlieb Gan (who was known as a pioneer of manganese and studied its properties), conducted research on the method of sulfuric acid production in the city of Gripsholm.

In the course of laboratory experiments in sulfuric acid, precipitation of red with an admixture of a light brown hue of the substance was found. When interacting with the soldering tube, sedimentary materials emanated from a light odor of odor and formed a lead queen. The Berlin scientist Martin Klaproth claimed that the presence of a characteristic smell indicates the presence of tellurium. A colleague of Berzelius also noted that in the mines where this sulfur for the acid is mined (in Falun), there is also a similar smell.

In the hope of finding a rare recently discovered metal (tellurium) in solution, the scientists began to study the sediment in more detail, but everything was in vain. After Berzelius collected all the products that accumulated over several months of obtaining sulfuric acid by burning sulfur, and also began to explore.

Studies have shown that a new, previously unknown element has similar properties to tellurium, but it is not. So the periodic table received a new element - selenium.

Origin of the name of the element

The history of the origin of the name of the new element is quite interesting. The Periodic Table of Mendeleev defines a new element as Selenium (Se). His name came from the name of our natural satellite.

Initially, in Russian publications, the element was called "selenium" (in the tenth years of the XIX century). Later, after 1835, the year the name "selenium" was adopted.

Properties of selenium

The formula of selenium is Se. The melting point of the substance is 217 (α-Se) and 170-180 degrees Celsius (β-Se), and it boils at 685 0 .

The degree of oxidation that selenium exhibits in the reactions: (-2), (+2), (+4), (+6), it is resistant to air, oxygen, water, hydrochloric acid and dilute sulfuric acid.

It is soluble in nitric acid of high concentration, "royal vodka", longer dissolves in alkaline environment with oxidation.

Forms of selenium

There are two modifications of selenium:

  1. Crystalline (monoclinic selenium of a- and b-forms, hexagonal selenium of g-form).
  2. Amorphous (powdery, colloidal and vitreous forms of selenium).

Amorphous red amorphous selenium modification. What it is? One of the unstable modifications of the element. Powdered and colloidal forms of selenium are obtained by reducing the substance from a solution of selenious acid H 2 SeO 3 .

Black vitreous selenium can be obtained by heating the element of any modification to a temperature of 220 degrees Celsius with rapid cooling.

Hexagonal selenium is gray. This modification, the most stable thermodynamically, can also be obtained by heating to the melting point with further cooling to a temperature of 180-210 degrees Celsius. It takes some time to withstand such a temperature regime.

Selenium oxide

There are a number of oxides that are formed by the interaction of selenium and oxygen: SeO 2 , SeO 3 , SeO, Se 2 O 5 . In this case, SeO 2 and SeO 3 are the anhydrides of selenide (H 2 SeO 3 ) and selenium (H 2 SeO 4 ) acids, which form salts of selenite and selenate. Selenium oxide SeO 2 (readily soluble in water) and is the most stable.

Interesting experiments on selenium

Before starting experiments with this element, it is worth remembering that any connections with selenium are poisonous, therefore it is necessary to take all safety measures, for example, to put on protective equipment and conduct reactions in a fume hood.

The color of selenium is manifested during a pleasant reaction to the eye. If sulfuric gas is passed through a flask with selenious acid, which is a good reducing agent, the resulting solution turns yellow, then orange, and eventually - blood red.

A weak solution will give an opportunity to obtain amorphous colloidal selenium. In the event that the concentration of selenious acid is high, during the reaction, the powder will precipitate from red to a dark-burgundy hue. It will be an amorphous powdery selenium of elementary form.

In order to bring the substance into the vitreous state, it is necessary to heat it and cool it down sharply. The color changes to black, but the red tint can be seen only if you look at the lumen.

The crystalline monoclinic selenium will be a little more complicated. To do this, take a small amount of red powder and mix with carbon disulphide. To the vessel with the mixture it is necessary to connect the reflux condenser and boil for 2 hours. Soon a light orange liquid with a light green tint will start to form, which will need to slowly evaporate in the containers under the filter paper.

Application of selenium

Selenium was first used in the ceramic and glass industries. About this tells us the "Handbook of rare metals" in 1965 edition.

Selenium is added to the glass mass in order to discolor the glass, removing the greenish shade, which gives an admixture of iron compounds. For the production of ruby glass in the glass industry, a compound of selenium and cadmium (cadmium silicate CdSe) is used. In the production of ceramics cadmelite gives it a red color, as well as stains enamels.

A bit of selenium is used as a filler in the rubber industry, as well as in the steel industry, in order that the resulting alloys have a fine-grained structure.

Most semiconductor technology is manufactured using selenium. This was the main reason for the rising cost of such a substance as selenium. The price increased from 3.3 to 33 dollars per kilogram in 1930 and 1956 respectively.

The cost of selenium in the world market in 2015 was 68 dollars per 1 kg. While in 2012 kilogram of this metal was worth about $ 130 per kilogram. Demand for selenium (the price is the confirmation) is falling due to the high supply.

The substance is also widely used in the manufacture of photographic equipment.

The presence of selenium in the human body

Our body contains about 10-14 milligrams of this substance, which is concentrated to a greater extent in organs such as the liver, kidneys, heart, spleen, testicles and spermatic cord in men, as well as in the nuclei of cells.

The need of the human body in such a trace element as selenium is low. Only 55-70 micrograms for adults. The maximum daily dose is 400 micrograms. Nevertheless, there is a disease called Keshan disease, which occurs when this element is deficient. Until the sixties, selenium was considered a poisonous substance, which has a negative effect on the human body. But after a detailed study, the reverse conclusions were drawn.

Often when detecting the pathological content of selenium, doctors can prescribe special drugs containing a combination of zinc-selenium-magnesium, substances that in the complex will fill its insufficiency in the body. Of course, not excluding products that contain selenium.

Effects on the body

Selenium has a very important role in the process of life:

  • It activates the immune system - "stimulates" leukocytes to a more active effect on harmful microorganisms (viruses);
  • Slows the aging process in the body;
  • Reduces the risk of arrhythmia, sudden coronary death or oxygen starvation due to a delay in the oxidation of cholesterol;
  • Accelerates the flow of blood to the brain, activating the mental activity, relieves the symptoms of depression and depression (fatigue, lethargy, depression and restlessness);
  • Inhibits the development of cancer cells, having antioxidant properties;
  • Actively selenium struggles with free radicals;
  • When interacting with vitamin E acts as an anti-inflammatory agent.

Of course, one can not ignore such an important property of the microelement as help in combating dangerous viruses: HIV / AIDS, hepatitis, Ebola fever.

Due to the presence of selenium, the virus lingers inside the cell; The substance prevents the spread of the virus through the body. But if selenium is not enough, then its function does not work properly.

Taking selenium in combination with iodine will help stop the progressing thyroid disease (lack of thyroxine), and in some cases stimulate regression of the disease (more often in children).

Also in medicine, selenium is used for the prevention of diabetes because it speeds up the consumption of glucose by the body.

A drug with vitamins can be administered to pregnant women. It helps to cope with the symptoms of toxicosis, relieve fatigue and cheer up.

Selenium deficiency

Why in the body can be a shortage of such a substance as selenium? What is this - "selenium deficiency" and how to deal with it? In fact, this is an unpleasant disease, despite the fact that it arises quite rarely.

It is important to know that the worst enemy of this substance is, of course, carbohydrates - flour, sweet. In combination with them, selenium is very poorly absorbed by the body and this can cause its lack.

What are the signs of a deficit? First of all, it is worth noting that with a deficit of selenium, the working capacity and general mood will decrease.

Lack of selenium weakens immunity, resulting in the body becoming more susceptible to various diseases, both mental and physical.

Also, with the deficiency of this substance in the body, the process of assimilation of vitamin E is disrupted.

The main signs of a lack of selenium are: pain in the muscles and joints, premature fatigue, anemia, acute kidney and pancreas diseases.

But if you feel any of the symptoms, in no case should you engage in medical self-medication. It is necessary to visit a doctor and consult about the need for taking certain medications. Otherwise, you can call yourself an excess of selenium, which is worse in some cases. For example, if a person with an oncological disease will take uncontrolled selenium, chemotherapy (chemotherapy) may not work.

Excess selenium

Over-saturation with selenium also produces a negative effect on the body. The main signs of the surplus are: damage to the hair and nails, damage to the teeth, fatigue and permanent nervous disorders, loss of appetite, the appearance of dermatitis, arthritis, as well as icterus and peeling of the skin.

But if you do not work at selenium mining facilities, or do not live near the places where this substance is extracted, then you can not be afraid of excess selenium in the body.

Products rich in selenium

Most selenium is found in meat and liver - pork, beef, chicken, duck or turkey liver. For example, in 100 grams of turkey liver contains 71, and in the pig - 53 micrograms of selenium.

In 100 grams of octopus meat contains 44.8 μg of selenium. Also in the diet include products such as shrimp, red fish, eggs, corn, rice, beans, barley and lentils, wheat, peas, broccoli, and inactive baker's yeast (processed with 60 degrees water heated up). Do not forget about nuts - pistachios, almonds, walnuts and peanuts also contain selenium, albeit in small quantities.

It is also worth remembering that when processing products the substance is lost, canned food and concentrates contain half the amount of selenium than fresh products. Therefore, whenever possible, it is necessary to consume as many fresh products containing selenium as possible.

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