Silicon (called silicon in Taiwan and Hong Kong) is a chemical element, its chemical symbol is Si, formerly known as silicon. The atomic number is 14, the relative atomic mass is 28.09, there are two kinds of allotropes, amorphous and crystalline, and allotropes include amorphous silicon and crystalline silicon. A metalloid element belonging to group IVA on the periodic table.

Crystalline silicon is steel gray, amorphous silicon is black, density is 2.4g/cm3, melting point is 1420°C, boiling point is 2355°C, crystalline silicon is atomic crystal, hard and shiny, and has semiconductor properties. The chemical properties of silicon are relatively active. It can combine with oxygen and other elements at high temperatures. It is insoluble in water, nitric acid and hydrochloric acid, but soluble in hydrofluoric acid and lye. It is used to make alloys such as ferrosilicon, silicon steel, etc., single crystal. Silicon is an important semiconductor material used to make high-power transistors, rectifiers, solar cells, and more. Silicon is widely distributed in nature, containing about 27.6% in the earth's crust, mainly in the form of silicon dioxide and silicate. Crystalline silicon is dark blue, very brittle, and is a typical semiconductor. Chemical properties are very stable. At room temperature, it is difficult to react with other substances except hydrogen fluoride.

Silicon uses:

①High-purity single crystal silicon is an important semiconductor material. Doping a small amount of group IIIA elements in single crystal silicon to form a p-type silicon semiconductor; doping a small amount of group VA elements to form n-type and p-type semiconductors combined together, can be made into solar cells, the radiation energy converted into electricity. It is a promising material in the development of energy.

② Metal ceramics, important materials for space navigation. The ceramic and metal are mixed and sintered to make a metal-ceramic composite material, which is resistant to high temperature, rich in toughness, and can be cut. It not only inherits the respective advantages of metal and ceramics, but also makes up for the congenital defects of both. It can be used in the manufacture of military weapons The first space shuttle "Columbia" can withstand the high temperature caused by friction when traversing the dense atmosphere at high speed, thanks to its shell made of 31,000 silicon tiles.

③ Optical fiber communication, the latest modern means of communication. The high-transparency glass fiber is drawn from pure silica, and the laser is transmitted forward through numerous total reflections in the path of the glass fiber, replacing the bulky cable. The optical fiber has high communication capacity. A glass fiber as thin as a human hair can transmit 256 telephone calls at the same time. It is also free from electrical and magnetic interference, not afraid of eavesdropping, and has a high degree of confidentiality. Optical fiber communication will revolutionize human life in the 21st century.

④ Silicone organic compounds with excellent performance. Silicone plastics, for example, are excellent waterproof coating materials. Spraying silicone on the four walls of the subway can solve the problem of water seepage once and for all. On the surface of ancient cultural relics and sculptures, a thin layer of silicone plastic can be applied to prevent moss from growing and resist wind, rain and weathering. The Monument to the People's Heroes on Tiananmen Square is treated with silicone plastic, so it will always be white and fresh.

Organosilicon compounds refer to compounds that contain Si-O bonds and at least one organic group is directly connected to the silicon atom. It is also customary to use those compounds that connect the organic group to the silicon atom through oxygen, sulfur, nitrogen, etc. Also used as organosilicon compounds. Among them, polysiloxanes composed of silicon-oxygen bonds (-Si-0-Si-) as the skeleton are the most numerous, the most deeply studied and the most widely used type of organosilicon compounds, accounting for more than 90% of the total dosage. .

Silicone materials have a unique structure:

(1) Sufficient methyl groups on Si atoms shield the high-energy polysiloxane backbone;

(2) C-H is non-polar, making the intermolecular interaction very weak;

(3) The Si-O bond length is long and the Si-O-Si bond angle is large.

(4) Si-O bond is a covalent bond with 50% ionic bond characteristics (covalent bond has directionality, ionic bond has no direction). Due to the unique structure of silicone, it combines the properties of inorganic materials and organic materials. It has the basic properties of low surface tension, small viscosity-temperature coefficient, high compressibility, high gas permeability, and has high and low temperature resistance, electrical insulation, oxidation resistance and stability. It is widely used in aerospace, electrical and electronic, construction, transportation, chemical industry, textile, food, light industry, medical and other industries. Among them, silicones are mainly used in sealing, bonding, lubrication, coating, surface activity, mold release, defoaming, foam suppression, waterproofing, moisture-proof, inert filling, etc. With the continuous growth of the quantity and variety of organic silicon, the application field has been continuously expanded, forming a unique and important product system in the field of new chemical materials. Many varieties are irreplaceable and indispensable for other chemicals. According to their different forms, silicone materials can be divided into: silane coupling agent (organic silicon chemical reagent), silicone oil (silicone grease, silicone emulsion, silicone surfactant), high temperature vulcanized silicone rubber, liquid silicone rubber, silicone resin, compound, etc.

Discovery In 1822, the Swedish chemist Bai Zeli reduced silicon tetrafluoride with potassium metal to obtain elemental silicon.