Silicon

Silicon is a chemical element in the periodic table that has the symbol Si and atomic number 14. Silicon is widely used as a semiconductor. A tetravalent metalloid, silicon is the second most abundant element in the Earth's crust, making up 25.7% of it by weight. Chemically the element is less reactive than its chemical analog carbon and occurs in clay, feldspar, granite, quartz and sand. This element is the principal component of glass, semiconductors, cement and ceramics.

Properties

General
Name, Symbol, Number	Silicon, Si, 14
Series	metalloid
Group, Period, Block	14 (IV), 3, p
Density, Hardness	2330 kg/m3, 6.5
Appearance	dark grey, bluish tinge
Atomic
Atomic weight	28.0855 amu
Atomic radius (calc.)	110 (111)pm
Covalent radius	111 pm
van der Waals radius	210 pm
Electron configuration	[Ne]3s2 3p2
e- 's per energy level	2, 8, 4
Oxidation states (Oxide)	4 (amphoteric)
Crystal structure	Cubic face centered
Physical
State of matter	solid (nonmagnetic)
Melting point	1687 K (2577 °F)
Boiling point	3173 K (5252 °F)
Molar volume	12.06 ×10-3 m3/mol
Heat of vaporization	384.22 kJ/mol
Heat of fusion	50.55 kJ/mol
Vapor pressure	4.77 Pa at 1683 K
Velocity of sound	__ m/s at __ K
Miscellaneous
Electronegativity	1.90 (Pauling scale)
Specific heat capacity	700 J/(kg*K)
Electrical conductivity	2.52 10-4/m ohm
Thermal conductivity	148 W/(m*K)
1st ionization potential	786.5 kJ/mol
2nd ionization potential	1577.1 kJ/mol
3rd ionization potential	3231.6 kJ/mol
4th ionization potential	4355.5 kJ/mol
5th ionization potential	16091 kJ/mol
6th ionization potential	19805 kJ/mol
7th ionization potential	23780 kJ/mol
8th ionization potential	29287 kJ/mol
9th ionization potential	33878 kJ/mol
10th ionization potential	38726 kJ/mol
Most Stable Isotopes
iso NA half-life DM DE MeV DP 28Si 92.23% Si is stable with 10 neutrons 29Si 4.67% Si is stable with 11 neutrons 30Si 3.1% Si is stable with 12 neutrons 32Si {syn} 276 y Beta- 0.224 32P
SI units & STP are used except where noted.

Notable Characteristics

Silicon when in its crystalline form has a metallic luster and a grayish color. Even though it is a relatively inert element, silicon is still attacked by halogens and dilute alkalis but most acids, except for hydrofluoric acid do not affect it. Elemental silicon transmits more than 95% of all wavelengths of infrared light.

Uses

Silicon is a very useful element that is vital to many human industries. Silicon dioxide in the form of sand and clay are an important ingredient of concrete and brick. Silicon is a very important element for plant and animal life. Diatoms extract silica from water to build their protective cell walls. Other uses;

• lt is a refractory material used in high-temperature material production and its silicates are used in making enamels and pottery.
• Silicon is an important consituant of steel.
• Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and is used to make window glass, containers, insulators, among many other uses.
• Silicon carbide is one of the most important abrasives.
• Ultrapure silicon can be doped with arsenic, boron, gallium, or phosphorus to make silicon for use in transistors, solar cells and other solid-state devices which are used in electronics and space-age industries.
• Used in lasers to produce coherent light of 4560 angstroms.

Hydrogenated amorphous silicon has shown promise in the production of economical solar cells for converting solar energy into electricity.

History

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

Sources

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

Measured by weight, silicon makes up 25.7% of the earth's crust and after oxygen is also the second most abundant element. Silicon is not found unbound in nature occurring most often as oxides and as silicates. Sand, amethyst, agate, quartz, rock crystal, flint, jasper, and opal are some of the forms in which the oxide appears. Granite, asbestos, feldspar, clay, hornblende, and mica are a few of the many silicate minerals.

Silicon is commercially prepared by the heating of silica and carbon in an electric furnace by using carbon electrodes. The Czochralski process is often used to make single silicon crystals that are used in solid-state/semiconductor devices.

In 1997 regular grade silicon (99% purity) cost about $ 0.50 per g.

Isotopes

Silicon has nine isotopes, with mass numbers from 25-33. Si-28 (the most abundant isotope, at 92.23%), Si-29 (4.67%), and Si-30 (3.1%) are stable; Si-32 is a radioactive isotope produced by argon decay. Its half-life, after much argument, has been determined to be approximately 276 years, and it decays by beta emission to P-32 (which has a 14.28 year half-life) and then to S-32.

Precautions

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.

Information sources and external links:

Los Alamos National Laboratory - Silicon
WebElements.com - Silicon
EnvironmentalChemistry.com - Silicon