14 aluminiumsiliconphosphorus


Periodic Table - Extended Periodic Table
Name, Symbol, Number silicon, Si, 14
Chemical series metalloids
Group, Period, Block 14, 3, p
Appearance as coarse powder,

dark gray with bluish tinge

Atomic mass 28.0855(3) g/mol
Electron configuration [Ne] 3s2 3p2
Electrons per shell 2, 8, 4
Physical properties
Phase solid
Density (near r.t.) 2.33 g·cm−3
Liquid density at m.p. 2.57 g·cm−3
Melting point 1687 K
(1414 °C, 2577 °F)
Boiling point 3538 K
(3265 °C, 5909 °F)
Heat of fusion 50.21 kJ·mol−1
Heat of vaporization 359 kJ·mol−1
Heat capacity (25 °C) 19.789 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1908 2102 2339 2636 3021 3537
Atomic properties
Crystal structure Face-centered cubic
Oxidation states 4
(amphoteric oxide)
Electronegativity 1.90 (Pauling scale)
Ionization energies
1st: 786.5 kJ·mol−1
2nd: 1577.1 kJ·mol−1
3rd: 3231.6 kJ·mol−1
Atomic radius 110 pm
Atomic radius (calc.) 111 pm
Covalent radius 111 pm
Van der Waals radius 210 pm
Magnetic ordering nonmagnetic
Thermal conductivity (300 K) 149 W·m−1·K−1
Thermal expansion (25 °C) 2.6 µm·m−1·K−1
Speed of sound (thin rod) (20 °C) 8433 m/s
Young's modulus 150 GPa
Bulk modulus 100 GPa
Mohs hardness 6.5
CAS registry number 7440-21-3
Selected isotopes
Main article: Isotopes of silicon
iso NA half-life DM DE (MeV) DP
28Si 92.23% Si is stable with 14 neutrons
29Si 4.67% Si is stable with 15 neutrons
30Si 3.1% Si is stable with 16 neutrons
32Si syn 132 y β- 13.020 32P
Not to be confused with Silicone.

Silicon (IPA: /ˈsɪlikən/, Latin: silicium) is the chemical element that has the symbol Si and atomic number 14. A tetravalent metalloid, silicon is less reactive than its chemical analog carbon. As the seventh or eighth most common element in the universe by mass, silicon occassionally occurs as the pure free element in nature, but is more widely distributed in dusts, planetoids and planets as various forms of silicon dioxide or silicate. On Earth, silicon is the second most abundant element (after oxygen) in the crust, making up 25.7% of the crust by mass.

Silicon has many industrial uses. Elemental silicon is the principal component of most semiconductor devices. Silicon is widely used in semiconductors because it remains a semiconductor at higher temperatures than the semiconductor germanium and because its native oxide is easily grown in a furnace and forms a better semiconductor/dielectric interface than almost all other material combinations.

In the form of silica and silicates, silicon forms useful glasses, cementes, and ceramics. It is also a component of silicones, a class-name for various synthetic plastic substances made of silicon, oxygen and hydrogen, often confused with silicon itself.

Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals. It is much more important to the metabolism of plants, particularly many grasses, and silicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopic diatoms.



Notable characteristics

In its elemental crystalline form, silicon has a gray color and a metallic luster which increases with the size of the crystal. It is similar to glass in that it is rather strong, very brittle, and prone to chipping. Even though it is a relatively inert element, silicon still reacts with halogens and dilute alkalis, but most acids (except for a combination of nitric acid and hydrofluoric acid) do not affect it. Elemental silicon transmits more than 95% of all wavelengths of infrared light. Pure silicon has a negative temperature coefficient of resistance, since the number of free charge carriers increases with temperature. The electrical resistance of single crystal silicon significantly changes under the application of mechanical stress due to the piezoresistive effect.



Silicon is a very useful element that is vital to many human industries. Silicon is used frequently in manufacturing computer chips and related hardware.


Silicon and alloys


Silicon compounds

See also category:Silicon compounds



Silicon (Latin silex, silicis, meaning flint) was first identified by Antoine Lavoisier in 1787, and was later mistaken by Humphry Davy, in 1800, for a compound. In 1811 Gay-Lussac and Thénard probably prepared impure amorphous silicon through the heating of potassium with silicon tetrafluoride. In 1824 Berzelius prepared amorphous silicon using approximately the same method as Lussac. Berzelius also purified the product by repeatedly washing it.

Because silicon is an important element in semiconductor and high-tech devices, the high-tech region of Silicon Valley, California, is named after this element.



Measured by mass, silicon makes up 25.7% of the Earth's crust and is the second most abundant element on Earth, after oxygen. Pure silicon crystals are only occasionally found in nature; they can be found as inclusions with gold and in volcanic exhalations. Silicon is usually found in the form of silicon dioxide (also known as silica), and silicate.

Silica occurs in minerals consisting of (practically) pure silicon dioxide in different crystalline forms (quartz, chalcedony, opal). Sand, amethyst, agate, quartz, rock crystal, flint, jasper, and opal are some of the forms in which silicon dioxide appears (they are known as "lithogenic", as opposed to "biogenic", silicas).

Silicon also occurs as silicates (various minerals containing silicon, oxygen and one or another metal), for example feldspar. These minerals occur in clay, sand and various types of rock such as granite and sandstone. Asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.

Silicon is a principal component of aerolites, which are a class of meteoroids, and also is a component of tektites, which are a natural form of glass.

See also category:Silicate minerals



Silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal, in an electric arc furnace using carbon electrodes. At temperatures over 1900 °C, the carbon reduces the silica to silicon according to the chemical equation

SiO2 + C → Si + CO2

Liquid silicon collects in the bottom of the furnace, and is then drained and cooled. The silicon produced via this process is called metallurgical grade silicon and is at least 98% pure. Using this method, silicon carbide, SiC, can form. However, provided the amount of SiO2 is kept high, silicon carbide may be eliminated, as explained by this equation:

2 SiC + SiO2 → 3 Si + 2 CO

In 2005, metallurgical grade silicon cost about $ 0.77 per pound ($1.70/kg).[1].



The use of silicon in semiconductor devices demands a much greater purity than afforded by metallurgical grade silicon. Historically, a number of methods have been used to produce high-purity silicon.


Physical methods

Silicon wafer with mirror finish (NASA)
Silicon wafer with mirror finish (NASA)

Early silicon purification techniques were based on the fact that if silicon is melted and re-solidified, the last parts of the mass to solidify contain most of the impurities. The earliest method of silicon purification, first described in 1919 and used on a limited basis to make radar components during World War II, involved crushing metallurgical grade silicon and then partially dissolving the silicon powder in an acid. When crushed, the silicon cracked so that the weaker impurity-rich regions were on the outside of the resulting grains of silicon. As a result, the impurity-rich silicon was the first to be dissolved when treated with acid, leaving behind a more pure product.

In zone melting, also called zone refining, the first silicon purification method to be widely used industrially, rods of metallurgical grade silicon are heated to melt at one end. Then, the heater is slowly moved down the length of the rod, keeping a small length of the rod molten as the silicon cools and resolidifies behind it. Since most impurities tend to remain in the molten region rather than resolidify, when the process is complete, most of the impurities in the rod will have been moved into the end that was the last to be melted. This end is then cut off and discarded, and the process repeated if a still higher purity was desired.


Chemical methods

Today, silicon is instead purified by converting it to a silicon compound that can be more easily purified than silicon itself, and then converting that silicon element back into pure silicon. Trichlorosilane is the silicon compound most commonly used as the intermediate, although silicon tetrachloride and silane are also used. When these gases are blown over silicon at high temperature, they decompose to high-purity silicon.

In the Siemens process, high-purity silicon rods are exposed to trichlorosilane at 1150 °C. The trichlorosilane gas decomposes and deposits additional silicon onto the rods, enlarging them according to chemical reactions like

2 HSiCl3 → Si + 2 HCl + SiCl4

Silicon produced from this and similar processes is called polycrystalline silicon. Polycrystalline silicon typically has impurity levels of less than 10-9.

At one time, DuPont produced ultrapure silicon by reacting silicon tetrachloride with high-purity zinc vapors at 950 °C, producing silicon according to the chemical equation

SiCl4 + 2 Zn → Si + 2 ZnCl2

However, this technique was plagued with practical problems (such as the zinc chloride byproduct solidifying and clogging lines) and was eventually abandoned in favor of the Siemens process.



The majority of silicon crystals grown for device production are produced by the Czochralski process, (CZ-Si) since it is the cheapest method available and it is capable of producing large size crystals. However, silicon single-crystals grown by the Czochralski method contain impurities since the crucible which contains the melt dissolves. For certain electronic devices, particularly those required for high power applications, silicon grown by the Czochralski method is not pure enough. For these applications, float-zone silicon (FZ-Si) can be used instead. It is worth mentioning though, in contrast with CZ-Si method in which the seed is dipped into the silicon melt and the growing crystal is pulled upward, the thin seed crystal in the FZ-Si method sustains the growing crystal as well as the polysilicon rod from the bottom. As a result, it is difficult to grow large size crystals using the float-zone method. Today, all the dislocation-free silicon crystals used in semiconductor industry with diameter 300mm or larger are grown by the Czochralski method with purity level significantly improved.


Different forms of silicon

One can notice the color change in silicon nanopowder. This is caused by the quantum effects which occur in particles of nanometric dimensions. See also Potential well, Quantum dot, and Nanoparticle



Silicon has numerous known isotopes, with mass numbers ranging from 22 to 44. 28Si (the most abundant isotope, at 92.23%), 29Si (4.67%), and 30Si (3.1%) are stable; 32Si is a radioactive isotope produced by argon decay. Its half-life, has been determined to be approximately 132 years, and it decays by beta emission to 32P (which has a 14.28 day half-life [2]) and then to 32S.



A serious lung disease known as silicosis often occurred in miners, stonecutters, and others who were engaged in work where siliceous dust was inhaled in great quantities.


Silicon-based life

Since silicon is similar to carbon, particularly in its valency, some people have proposed the possibility of silicon-based life. This concept is especially popular in science fiction. One main detraction for silicon-based life is that unlike carbon, silicon does not have the tendency to form double and triple bonds.

Although there are no known forms of life that rely entirely on silicon-based chemistry, there are some that rely on silicon minerals for specific functions. Some bacteria and other forms of life, such as the protozoa radiolaria, have silicon dioxide skeletons, and the sea urchin has spines made of silicon dioxide. These forms of silicon dioxide are known as biogenic silica. Silicate bacteria use silicates in their metabolism.

Life as we know it could not have developed based on a silicon biochemistry. The main reason for this fact is that life on Earth depends on the carbon cycle: autotrophic entities use carbon dioxide to synthesize organic compounds with carbon, which is then used as food by heterotrophic entities, which produce energy and carbon dioxide from these compounds. If carbon was to be replaced with silicon, there would be a need for a silicon cycle. However, silicon dioxide precipitates in aqueous systems, and cannot be transported among living beings by common biological means.

As such, another solvent would be necessary to sustain silicon-based life forms; it would be difficult (if not impossible) to find another common compound with the unusual properties of water which make it an ideal solvent for carbon-based life. Larger silicon compounds analogous to common hydrocarbon chains (silanes) are also generally unstable owing to the larger atomic radius of silicon and the correspondingly weaker silicon-silicon bond; silanes decompose readily and often violently in the presence of oxygen making them unsuitable for an oxidizing atmosphere such as our own. Silicon also does not readily participate in pi-bonding (the second and third bonds in triple bonds and double bonds are pi-bonds) as its p-orbital electrons experience greater shielding and are less able to take on the necessary geometry. Furthermore, although some silicon rings (cyclosilanes) analogous to common the cycloalkanes formed by carbon have been synthesized, these are largely unknown. Their synthesis suffers from the difficulties inherent in producing any silane compound, whereas carbon will readily form five-, six-, and seven-membered rings by a variety of pathways (the Diels-Alder reaction is one naturally-occurring example), even in the presence of oxygen. Silicon's inability to readily form long silane chains, multiple bonds, and rings severely limits the diversity of compounds that can be synthesized from it. Under known conditions, silicon chemistry simply cannot begin to approach the diversity of organic chemistry, a crucial factor in carbon's role in biology.

However, silicon-based life could be construed as being life which exists under a computational substrate. This concept is yet to be explored in mainstream technology but receives ample coverage by sci-fi authors.

A. G. Cairns-Smith has proposed that the first living organisms to exist were forms of clay minerals - which were probably based around the silicon atom.



For examples of silicon compounds see silicate, silane (SiH4), silicic acid (H4SiO4), silicon carbide (SiC), silicon dioxide (SiO2), silicon tetrachloride (SiCl4), silicon tetrafluoride (SiF4), and trichlorosilane (HSiCl3).

See also category:Silicon compounds




See also


External links

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