Silicon Element Facts

28.0855
Silicon

Silicon crystal structure.

General:

Name: Silicon	Symbol: Si
Type: Non-Metal, Carbon group	Atomic weight: 28.0855
Density @ 293 K: 2.33 g/cm³	Atomic volume: 12.1 cm³/mol
Discovery of Silicon In 1789, the French chemist Antoine Lavoisier proposed that quartz (crystalline silicon dioxide) was likely to be the oxide of an element which was very common but not yet identified or isolated. ⁽¹⁾ It is possible that in England in 1808 Humphry Davy isolated partly pure silicon for the first time, but he did not realize it. ⁽²⁾ In 1811, French chemists Joseph L. Gay-Lussac and Louis Jacques Thénard may also have made impure silicon by reacting potassium with what we would now call silicon tetrafluoride to produce a reddish brown solid which was probably amorphous silicon. They did not, however, attempt to purify the new substance they had made. ^{(3), (4)} In 1824 Swedish chemist Jöns Jakob Berzelius produced a sample of amorphous silicon, a brown solid, by reacting potassium fluorosilicate with potassium, purifying the product with repeated washing. He named the new element silicium. ^{(3), (4)} At that time, the concept of semiconductors lay a century in the future and scientists debated whether the new element was a metal or nonmetal. Berzelius believed it was a metal while Humphry Davy thought it was a nonmetal. ⁽⁵⁾ The problem was that the new element was a better conductor of electricity than nonmetals, but not as good a conductor as a metal should be. Silicon was given its name in 1831 by Scottish chemist Thomas Thomson. He retained part of Berzelius's name, from 'silicis', meaning flint. He changed the element's ending to on because the element was more similar to nonmetals boron and carbon than it was to metals such as calcium and magnesium. (Silicis, or flint, of course, was probably our first use of silicon dioxide. ^{(4), (6)}.) In 1854 Henri Deville produced crystalline silicon for the first time using an electrolytic method. He electrolyzed an impure melt of sodium aluminum chloride to produce aluminum silicide. The aluminum was removed with water, leaving silicon crystals. ⁽⁴⁾

States

State (s, l, g): solid
Melting point: 1687 K (1414 ^oC)	Boiling point: 3538 K (3265 ^oC)

Energies

Specific heat capacity: 0.71 J g^-1 K^-1	Heat of atomization: 456 kJ mol^-1
Heat of fusion: 50.21 kJ mol^-1	Heat of vaporization: 359 kJ mol^-1
1^st ionization energy: 786.4 kJ mol^-1	2^nd ionization energy: 1577 kJ mol^-1
3^rd ionization energy: 3231.4 kJ mol^-1	Electron affinity: 133.6 kJ mol^-1

Oxidation & Electrons

Shells: 2,8,4	Electron configuration: [Ne] 3s² 3p²
Minimum oxidation number: -4	Maximum oxidation number: 4
Min. common oxidation no.: -4	Max. common oxidation no.: 4
Electronegativity (Pauling Scale): 1.9	Polarizability volume: 5.4 Å³

Reactions

Reaction with air: none	Reaction with 6 M HCl: none
Reaction with 15 M HNO₃: none	Reaction with 6 M NaOH: mild, ⇒ silicates

Compounds

Oxide(s): SiO₂	Chloride(s): SiCl₄, Si₂Cl₆ + more
Hydride(s): SiH₄ (silane), Si₂H₆ + more

Radius

Atomic radius: 110 pm	Ionic radius (1+ ion): pm
Ionic radius (2+ ion): pm	Ionic radius (3+ ion): pm
Ionic radius (2- ion): pm	Ionic radius (1- ion): pm

Conductivity

Thermal conductivity: 149 W m^-1 K^-1

Electrical conductivity: 1.2 x 10^-5 S cm^-1

Abundance & Isotopes

Abundance earth's crust: 28 % by weight, 21 % ppm by moles
Abundance solar system: 900 parts per million by weight, 40 parts per million by moles
Cost, pure: $5.4 per 100g
Cost, bulk: $0.17 per 100g
Source: Silicon is the second most abundant element in Earth's crust, after oxygen and the eighth most abundant in the Universe. It is most commonly found as silicon dioxide (silica). Two elements, silicon and oxygen, make up almost three-quarters of our planet's crust. Commercial quantities of silicon are obtained by the reaction of silicon dioxide and carbon in an electric furnace using carbon electrodes. The carbon reduces the silicon dioxide to silicon. Silicon produced in this way is about 98% pure. Very high purity silicon for semiconductors is obtained using the Siemens process; the silicon is reacted to produce trichlorosilane, which is first purified by distillation, then reacted with purified hydrogen on high purity silicon rods at 1150 ^oC to yield high purity, polycrystalline silicon with hydrochloric acid byproduct. Impurities in the silicon are about 1 part per billion or less.
Isotopes: Silicon has 14 isotopes whose half-lives are known, with mass numbers 22 to 36. Of these, three are stable: ²⁸Si, ²⁹Si and ³⁰Si.

1. R.W. Cahn, Silicon: Child and Progenitor of Revolution., Into The Nano Era, Springer Series in Materials Science, Volume 106. (2009) p3.
2. Thomas Edward Thorpe, Humphry Davy, Poet and Philosopher., (1896).
3. Mary Elvira Weeks, Discovery of the Elements., (2003) p162, Kessinger Publishing Reprints.
4. John Emsley, Nature's Building Blocks: An A-Z Guide to the Elements., (2002) p387. Oxford University Press.
5. H. R. Huff, U. Gösele, H. Tsuya, Semiconductor Silicon., (1998) p70, The Electrochemical Society.
6. Keith B. Hutton, Chemistry. (2001) p224. Routledge.

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Structure: diamond structure	Color: brown (amorphous), gray-black (crystalline)
Hardness: 7 mohs
How silicon is made into wafers and computer chips. Not only about silicon, how the next generation of electronic devices may work.	Harmful effects: Silicon is not known to be toxic, but if breathed in as a fine silica/silicate dust it may cause chronic respiratory problems. Silicates such as asbestos are carcinogenic. Characteristics: Silicon is a hard, relatively inert metalloid and in crystalline form is very brittle with a marked metallic luster. Silicon occurs mainly in nature as the oxide and as silicates. The solid form of silicon does not react with oxygen, water and most acids. Silicon reacts with halogens or dilute alkalis. Silicon also has the unusual property that (like water) it expands as it freezes. Four other elements expand when they freeze; gallium, bismuth, antimony and germanium Uses: Silicon chips are the basis of modern electronic and computing. The silicon must be ultrapure, although depending on final use it may be doped with part per million levels of arsenic, boron, gallium, germanium, or phosphorus. Silicon is alloyed with aluminum for use in engines as the presence of silicon improves the metal's castability. Silicon can enhance iron's magnetic properties is it is also an important component of steel, which it toughens. Silicon carbide, more commonly called carborundum, is extremely hard and is used in abrasives. Silica (SiO₂) in sand and minerals in clay is used to make concrete and bricks. Silica, as sand, is also the main constituent of glass. Pure, crystalline silicon dioxide (quartz) resonates at a very precise frequency and is used in high-precision watches and clocks. Silicones are important silicon based polymers. Having heat-resistant, nonstick, and rubber-like properties, silicones are often used in cookware, medicine (implants), and as sealants, adhesives, lubricants, and for insulation.