Silicon Hexoxide Formula
Silicon can form simple binary covalent compounds with most halogens. However, these compounds are contaminated with other elements and require special chemical reactions to purify them.
Silica is abundant in the Earth’s crust and can be found in crystalline forms such as quartz, jasper, opal, feldspar, micas, olivines and pyroxenes as well as in brown amorphous powder known as “dirty beach sand”. It behaves like a metalloid and is capable of expanding its valence shell.
Silicon
Silicon (Si) is the eighth most abundant element in the universe. It is a metalloid, which means that it has properties of both metals and non-metals. It is used for a wide variety of applications, including insulation, cookware, high temperature lubricants and in medical equipment. In its solid state, it is a hard material that has the ability to be formed into many shapes. It can be combined with a number of other materials, including rubbers and plastics, to form silicone polymers. These have a wide range of useful properties, including flexibility, resistance to chemical attack and impermeability to water. They can withstand extremely high and low temperatures, making them ideal for use in industrial and automotive applications.
In its pure form, Si is very rare. It is usually found in compounds, most commonly as silica. To obtain pure silicon, it must be chemically extracted from these complexes, which is done by heating the compound to very high temperatures and then adding carbon, which reduces it to pure silicon. This process is called carbo-silicon synthesis. It is very energy-intensive, and the resulting pure silicon is very expensive.
Because of this, a great deal of research has been conducted on finding ways to make the process more efficient. For example, some of the waste silicon generated by the manufacture of semiconductor wafers is re-used in the synthesis of silanes and other organic silicon compounds. This helps to lower the cost of the raw material, and may lead to the development of a more efficient way of producing semiconductor grade silicon.
A large family of silicon compounds is known as silanes, which are the silicon analogs of alkane hydrocarbons. They consist of a chain of silicon atoms covalently bound to hydrogen atoms. The general formula for a silane is SinH2n+2. Silanes can also have other functional groups attached to the silicon, just as carbon alkanes can have carbon-carbon bonds. The IUPAC nomenclature for silanes includes prefixes that indicate the number of silicons present, and suffixes that denote the number of hydrogens. For example, mono-silanes are named as SiH2, di-silanes as SiH3, tetra-silanes as SiH4, and penta-silanes as SiH5.
Silicates
Many common rocks are made from silicates. In the simplest silicates (isosilicates or orthosilicates) the silicon atom sits at the center of an idealized tetrahedron that has four oxygen atoms around it as corner atoms. Each oxygen atom bonds covalently to two silicon atoms, following the octet rule. These tetrahedra form a strong crystal lattice. Silicate minerals are then classified based on the length and crosslinking of these silica-oxygen bonds in their crystal structures, and by the presence or absence of other cations that can be attached to the silicon.
Minerals that contain only single chain silicate anions are called phyllosilicates, because their structure is similar to that of a leaf. In sheet silicates such as muscovite (K2MgSiO3), each tetrahedron shares three oxygen atoms with its neighbors. This type of silicate is very easily cleaved. Other tectosilicates form a more solid framework of three-dimensional networks that link these tetrahedra into larger units known as siliceous octahedra. These are also easy to cleave and form the rock gneiss.
Other cations can be linked to these silicon-oxygen tetrahedra, including Lithium (Li+), Sodium (Na+), Potassium (K+), Magnesium (Mg2+), Calcium (Ca2+), Zinc (Zn2+), Aluminum (Al3+) and Beryllium (Be2+). These ions are typically not part of the anionic crystal lattice but serve to balance the positive charge of the Si-O bonds, providing the mineral with its characteristic hardness and brittleness.
Some silicates, however, contain a mixture of both types of silicate anions. This is because Al+3 can substitute for Si+4 in these tetrahedral clusters, or it can go into 6-fold coordination with oxygen atoms. These substitutions can lead to complex crystal structures such as those found in the cyclosilicate minerals benitoite (BaTi(SiO3)3), cordierite (Mg2Al3[Si3O8]) and halite (Na2SiO3). The latter contains six-membered ring clusters [SiO3[Si4O12]]. The structures of these minerals are characterized by complex interplay between the different components of their silica-oxygen molecules. These crystalline structures are well-suited for study by single resonance NMR spectroscopy under MAS.