One of the most popular elements in engineering and industry is silicon. To this he owes his unusual properties. Today there are many different compounds of this element, which play an important role in the synthesis and creation of technical products, utensils, glass, equipment, building and decoration materials, jewelry and other industries.
General characteristics of silicon
If we consider the position of silicon in the periodic system, then we can say this:
- Located in group IV of the main subgroup.
- Sequence number 14.
- Atomic mass 28,086.
- Chemical symbol Si.
- The name is silicon, or in Latin - silicium.
- The electronic configuration of the outer layer is 4e: 2e: 8e.
The silicon crystal lattice is similar to a diamond lattice. Atoms are located in the nodes, its type is cubic face-centered. However, due to the longer bond length, the physical properties of silicon are very different from the properties of allotropic carbon modification.
Physical and chemical properties
There are two allotropic modifications of this element: amorphous and crystalline. They are very similar. However, as in the case of other substances, the main difference between them is the crystal lattice of silicon.
In this case, both modifications are powders of different colors.
1. Crystalline silicon is a dark gray shiny powder similar to metal. Its structure corresponds to diamond, but its properties are excellent. He has:
- fragility;
- low hardness;
- semiconductor properties;
- melting point 1415 0 C;
- a density of 2.33 g / cm 3 ;
- boiling point 2700 0 .
Its chemical activity is low compared to another allotropic form.
2. Amorphous silicon - brown-brown powder, has the structure of highly disordered diamond. The chemical activity is quite high.
In general, it should be noted that silicon does not like to enter into reactions. To make it react, a temperature of at least 400-500 ° C is needed. Under these conditions, various chemical compounds of silicon are formed. Such as:
- oxides;
- halides;
- silicides;
- nitrides;
- borides;
- carbides.
It is possible that silicon interacts with nitric acid or alkali, which is called the etching process. Organosilicon compounds are widely distributed , which today are becoming more widespread.
Being in nature
Silicon in nature is contained in a fairly significant amount. It is in second place after oxygen in terms of prevalence. Its mass fraction is about 30%. Sea water also contains this element in an approximate concentration of 3 mg / L. Therefore, it cannot be said that silicon in nature is a rare element.
On the contrary, there are many different rocks and minerals in which it is found and from which it can be mined. The most common natural silicon compounds are as follows:
- Silica. The chemical formula is SiO 2 . There is a fairly wide variety of forms of minerals and rocks based on it: sand, flint, feldspar, quartz, rock crystal, amethyst, chalcedony, carnelian, opal, jasper and others.
- Silicates and aluminosilicates. Kaolin, spars, mica, silicic acid salts, asbestos, talc.
Thus, silicon is widely distributed in nature, and its compounds are popular and in demand among people for technical applications.
Silicon and its compounds
Since in its pure form the element under consideration cannot exist, therefore its various compounds are important. From a chemical point of view, it can exhibit three degrees of oxidation: +2, +4, -4. Based on this, as well as on its inertness, but with a special structural lattice, it forms the following main types of substances:
- binary compounds with non-metals (silane, carbide, nitride, phosphide and so on;
- oxides;
- silicic acid;
- metal silicates.
Let us consider in more detail the importance of silicon and its compounds, which are the most common and in demand for people.
Silicon oxides
There are two varieties of this substance expressed by the formulas:
However, the most common is dioxide. It exists in nature in the form of very beautiful semiprecious stones:
- agate;
- chalcedony;
- opal;
- cornelian;
- jasper;
- amethyst;
- rhinestone.
The use of silicon in this form has found its application in the manufacture of jewelry. Incredibly beautiful gold and silver jewelry are made with these semiprecious and ornamental stones.
A few more variations of silicon dioxide:
- quartz;
- river and quartz sand ;
- flint;
- feldspars.
The use of silicon in these forms is implemented in construction work, engineering, electronics, the chemical industry, and metallurgy. All together, the listed oxides belong to a single substance - silica.
Silicon carbide and its application
Silicon and its compounds are materials of the future and the present. One such material is carborundum or carbide of this element. The chemical formula is SiC. It is found in nature in the form of the mineral moissanite.
In its pure form, the combination of carbon and silicon are beautiful transparent crystals resembling diamond structures. However, for technical purposes, green and black colored substances are used.
The main characteristics of this substance, allowing its use in metallurgy, technology, and the chemical industry, are as follows:
- wide-gap semiconductor;
- very high degree of strength (7 on the Mohs scale);
- resistant to high temperatures;
- excellent electrical stability and thermal conductivity.
All this allows the use of carborundum as an abrasive material in metallurgy and chemical synthesis. And also on its basis to produce LEDs of a wide spectrum of action, parts for glass melting furnaces, nozzles, torches, jewelry (moissanite is valued higher than cubic zirconia).
Silane and its meaning
The hydrogen compound of silicon is called silane and cannot be obtained by direct synthesis from the starting materials. To obtain it, silicides of various metals are used, which are treated with acids. As a result, gaseous silane is released and a metal salt is formed.
Interestingly, the compound in question never forms alone. The reaction always results in a mixture of mono-, di- and trisilane, in which silicon atoms are interconnected in chains.
By their properties, these compounds are strong reducing agents. At the same time, they themselves are easily oxidized by oxygen, sometimes with an explosion. With halogens, reactions are always violent, with a large release of energy.
The areas of application of silanes are as follows:
- Reactions of organic syntheses, resulting in the formation of important organosilicon compounds - silicones, rubbers, sealants, lubricants, emulsions and others.
- Microelectronics (liquid crystal monitors, integrated technical circuits, etc.).
- Obtaining ultra-pure polysilicon.
- Dentistry with prosthetics.
Thus, the importance of silanes in the modern world is high.
Silicic acid and silicates
The hydroxide of the element in question is different silicic acids. Allocate:
- meta;
- ortho;
- polysilicon and other acids.
All of them share common properties - extreme instability in a free state. They decompose easily under the influence of temperature. Under ordinary conditions, they do not last long, turning first into sol, and then to gel. After drying, such structures are called silica gels. They are used as adsorbents in filters.
Important, from an industrial point of view, are silicic acid salts - silicates. They are the basis for obtaining such substances as:
- glass;
- concrete;
- cement;
- zeolite;
- kaolin;
- china;
- faience;
- crystal;
- ceramics.
Silicates of alkali metals are soluble, all the rest are not. Therefore, sodium and potassium silicate is called liquid glass. Ordinary stationery glue - this is the sodium salt of silicic acid.
But the most interesting compounds are still glass. What variants of this substance have not been invented! Today they get color, optical, matte options. Glassware is striking in its splendor and diversity. By adding certain metal oxides and non-metals to the mixture, a wide variety of glass types can be obtained. Sometimes even the same composition, but a different percentage of the components leads to a difference in the properties of the substance. An example is porcelain and faience, the formula of which is SiO 2 * AL 2 O 3 * K 2 O.
Quartz glass is a form of highly pure product whose composition is described as silicon dioxide.
Discoveries in the field of silicon compounds
Over the past few years of research, it has been proven that silicon and its compounds are the most important participants in the normal state of living organisms. With a deficiency or excess of this element, diseases such as:
- cancer;
- tuberculosis;
- arthritis;
- cataract;
- leprosy;
- dysentery;
- rheumatism;
- hepatitis and others.
The processes of aging of the body themselves are also associated with the quantitative content of silicon. Numerous experiments on mammalian animals have proved that with a deficiency of an element, heart attacks, strokes, cancer occur and the hepatitis virus is activated.