What is silicon element? Who discovered silicon, what are the properties, compounds and the uses of silicon element.
Silicon; symbol Si, is a nonmetallic element of great importance to man. Present in stars and meteorites, it constitutes about 27.6 % of the earth’ s crust by weight and is the second most abundant element on earth, after oxygen. It is found in animal skeletons and plant tissues and forms the cell walls of diatoms. The element does not occur naturally on earth in the free state. It was first isolated by the English chemist Sir Humphry Davy in 1800 and the French chemists Louis Thenard and Joseph Gay-Lussac in 1811, but was not identified as an element until 1826 by the Swedish chemist Jakob Berzelius. Crystalline silicon was first prepared by the French chemist Henri Sainte-Claire Deville in 1854.
Properties,
Located in Group IVA of the periodic table, silicon is one of the carbon family of elements. Its atomic number is 14 and its atomic weight 28.086. In its erystalline fono it is a black to dark gray, brittle solid with a high metallic luster. In its amorphous form it is dark brown. The element has a specific gravity of 2.33 and it is one of the harder solids, with a hardness of 7 on the Mohs scale. Silicon melts at 1410° C (2570° F) and boils at 2355° C ( 4271°F). Silicon is a poor conductor of electricity and it expands very little when it is heated. There are three stable isotopes in nature.
Silicon has a valence of + 4. It is not a reactive element. Practically insoluble in water, it is unaffected by most acids except hydrofluoric acid. However, it combines with the halogens and reacts with alkalis even in dilute solutions, to form silicates and hydrogen. Its affinity for hydrogen is weak, compared to that of carbon, and in nature the element is found mainly in combination with oxygen.
Preparation and Uses:
Although silicon can be prepared in several ways, it is generally made commercially by heating the dioxide, silica (SiO2), with coke in an electric fumace. Zone refining of the element yields very high-purity silicon, as does decomposition of silicon tetraiodide (SiI4) and trichlorosilane (SiHCl3). High-purity silicon is of great importance in the electronics industries. Doped with elements such as boron, gallium, phosphorus, and arsenic, it is used in making transistors, silicon diodes, and other semiconductors.
Silicon of ordinary purity is used in alloys, which the element forms with most metals. Such alloys include ferrosilicon, used in making very resistant silicon steels and metallic magnesium, and silicon copper, combined with tin to make the silicon bronze used in telephone and telegraph wires, The element is also combined with certain ceramic materials to make cermets and other special refractories, and it serves as a reducing agent of metallic oxides in some high-temperature reactions.
Compounds:
Silicon occurs in the form of silica and silicates in rocks and in minerals such as sands, clays, and feldspars, to name a very few of these important natural compounds. In fact, the earth’s crust may be thought of as essentially a network of silicon and oxygen atoms. Of the many silicon compounds in commercial use, only a few can be mentioned here. Among them are the silanes and their derivatives, such as monosilane (SiH4) and disilane (Si2H6), and the organic polymers called silicones. Sodium silicate is better known as water glass, and silicon carbide is valued for its hardness.
