Silicon (Taiwan, Hong Kong) is a chemical element. Its chemical symbol is Si, formerly known as silicon. Atomic number 14, relative atomic mass 28.0855, there are amorphous silicon and crystalline silicon two isoforms, belonging to the third cycle of the periodic table, IVA group metal elements. Silicon is one of the very common elements, however, it rarely appears in the form of simple substance in nature, but in the form of complex silicate or silica, widely exists in rock, gravel, dust. Silicon is the eighth largest in the universe. In the crust, it is the second richest element, making up 26.4 percent of the total mass of the earth's crust, second only to the first oxygen (49.4 percent).
Silicon has obvious non-metallic properties and can be dissolved in alkali - metal hydride solutions, producing (partial) silicates and hydrogen.
The silicon atom is in the fourth main family of the periodic table. Its atomic number is Z= 14, and there are 14 electrons outside the core. The electron is outside the nucleus, and it is surrounded by layers of low silicon atoms, which are called the shell structure of the electron. The first layer of the silicon atom has two electrons, and the second layer has eight electrons to reach the stable state. There are four electrons in the outermost shell that are valence electrons, which play a leading role in the electrical conductivity of silicon atoms.
Because of silicon atoms have such a structure, so there are some special properties: the outermost four valence electrons to silicon atoms in a metastable structure, these valence electrons make the silicon atoms by covalent bonds in combination with each other, because a covalent bond is strong, the silicon has high melting point and density; Chemical properties are relatively stable, and it is difficult to react with other substances (except fluoride and lye) in normal temperature. There is no obvious free electron in silicon crystal, able to conduct electricity, but the conductivity is not as high as metal, and as the temperature increases, it has a semiconductor property.
It can be used as a non-metallic role such as halogen, nitrogen, carbon and other metals such as Mg, Ca, Fe, Pt, etc. The formation of silicification. Insoluble in common inorganic acid, soluble in alkali solution, and hydrogen is released to form the corresponding alkali metal silicate solution, at the red heat temperature, and water vapor can function.
In the laboratory, magnesium powder can be used to restore powdery silicon dioxide in the heat, and the magnesium oxide and magnesium powder produced with dilute acid, then washed with hydrofluoric acid to remove the silicon dioxide that did not work. This method is not pure amorphous silicon, which is brown and black powder. Silicon is produced in an electric arc furnace to restore silica (more than 99% of SiO2 content). The reducing agent used is petroleum coke and coke. When using dc arc furnace, it can replace charcoal with petroleum coke. The ash content of petroleum coke is low (0.3% ~ 0.8%), and the high quality silicon (SiO2 is greater than 99%) can be used directly to produce high quality silicon for making silicon steel sheet. High purity semiconductor silicon at 1200 ℃ of hot silicon rods with hydrogen reduction of high purity chemical hydrogen silicone SiHCl3 or SiCl4. Ultra-pure monocrystalline silicon can be prepared by direct or regional melting method.
Silicon is one of the essential trace elements in the body. Weight: 0.026%. Silicon and silicon-containing dust are the most harmful to human beings and are caused by silicosis. Silicosis is one of the most serious occupational diseases. Miners, stone processing workers and other workers who have been exposed to silica dust should take the necessary precautions. 
Silicon in connective tissue, cartilage formation, silicon is required, the silicon to link to each other, glycosaminoglycan and mucopolysaccharide binds to proteins, the formation of fibrous structure, thus increasing the elasticity of connective tissue and intensity, maintain the integrity of the structure; Silicon is involved in calcification of the bone, and it works at the initial stage of calcification. The silicon in the food can increase the rate of calcification, especially when the calcium intake is low. About 21 percent of the amino acid in collagen is hydroxyproline, which is hydroxylated with proline hydroxylase, which shows that silicon is needed for maximum vitality. The results show that silicon is one of the components of collagen through the analysis of collagen from different sources.
Reference intake: because there is no body silicon requirements of experimental data, so it is difficult to put forward appropriate human daily demand for silicon, by animal experiments, if silicon is easy to absorb, every day the body's requirements for 2 ~ 5 mg. But most of the silicon in the diet is not easily absorbed, and the recommended intake is about 5 to 10mg per day. It is considered appropriate to take 20 to 50mg daily.