Silicon dioxide Formula
Silicon dioxide, also known as silicon (IV) oxide or silica, is a chemical compound extensively found in quartz and sand. It is very used in the manufacture of electronic components.
Formula and structure: The silicon dioxide chemical formula is SiO2. Its molar mass is 60.08 g mol-1. Silicon dioxide is an oxide formed by Si+4 and O-2. The compound is mostly found in the crystalline form, for example as quartz, which is formed by a cation Si central, coordinated to 4 anion O, so that the structure of silica has a tetrahedral geometry. SiO2 can also be found as an amorphous solid or other crystalline forms as rhombohedral, hexagonal, cubic, nonclinical or ortorhombic geometry. Its chemical structure can be written as below, in the common representations used for organic molecules.
Occurrence: Silicon dioxide is a compound largely found in nature. It is the main component of mineral such as quartz, tridymite, amethyst, cristobalite, agateor sand. It is also present in the composition of many plants and in consequence, it can also be ingested by herbivores.
Preparation: Although most of silicon dioxide is extracted through quartz mining, it can also be prepared through the acid neutralization of an aqueous alkali metal silicate solution. This method is known as wet process and produces amorphous SiO2 particles.
Na2Si3O7 + H2SO4 → 3 SiO2 + Na2SO4 + H2O
Other methods let the production of pyrogenic silica and it consists on the combustion of silanes such as silicon tetrachloride, in an oxygen-hydrogen burner. The products are fine particles aggregates of 100 - 400 nm in diameter.
SiCl4 + 2 H2 + O2 → SiO2 + 4 HCl
Physical properties: Silicon dioxide is a transparent to gray, odorless, crystalline or amorphous solid. Its melting and boiling point are 1600 ºC and 2230 ºC, respectively. Its density is 2.65 g mL-1. It is insoluble in water and acid. It is soluble in hydrofluoric acid.
Chemical properties: Silicon dioxide is not very reactive compound due the polarity of molecule is zero. The Si forms two double bonds with the oxygen, thus it is a very stable molecule. Moreover, it has a high dielectric strength, thus it is very used as insulator and semiconductor.
Uses: Silicon dioxide has many uses in chemical, electronic and pharmaceutical industries. In chemical industry, in the production of adhesives and sealants, adsorbents and absorbents, ceramic, porcelain, anti-adhesives, corrosion inhibitors, dyes and paint additives. It is also used to produce agricultural chemicals. In pharmaceutical industries as additive of food and medicines to absorb water. SiO2 is the main component in the optical fibers for telecommunication. Silicon dioxide is extensively used as precursor to obtain glass and silicon, through the reaction:
SiO2 + 2 C → Si + 2 CO
Health effects/safety hazards: Silicon dioxide can cause serious eye irritation or damage. It can also cause respiratory irritation. This chemical compound may produce cancer by prolonged exposure. It is not flammable.
Ionic and Metallic Bonding
Boron tribromide Formula