Silicon: the essentials
Silicon is present in the sun and stars and is a principal component of a class of meteorites known as aerolites. Silicon makes up 25.7% of the earth's crust by weight, and is the second most abundant element, exceeded only by oxygen. It is found largely as silicon oxides such as sand (silica), quartz, rock crystal, amethyst, agate, flint, jasper and opal. Silicon is found also in minerals such as asbestos, feldspar, clay and mica.
Silicon is important in plant and animal life. Diatoms in both fresh and salt water extract silica from the water to use as a component of their cell walls. Silicon is an important ingredient in steel. Silicon carbide is one of the most important abrasives. Workers in environments where silicaceous dust is breathed may develop a serious lung disease known as silicosis.
- Name: silicon
- Symbol: Si
- Atomic number: 14
- Relative atomic mass (Ar): 28.0855 (3) [see note r]
- Standard state: solid at 298 K
- Colour: dark grey with a bluish tinge
- Classification: Semi-metallic
- Group in periodic table: 14
- Group name: (none)
- Period in periodic table: 3
- Block in periodic table: p-block
- Electron shell structure: 2.8.4
- CAS Registry ID: 7440-21-3
Hydrolysis and condensation of substituted chlorosilanes can be used to produce a very great number of polymeric products, or silicones. These range from liquids to hard, glasslike solids with many useful properties.
Elemental silicon transmits more than 95% of all wavelengths of infrared and and has been used in lasers to produce coherent light at 456 nm.
Silicon: historical information
JΔns Jacob Berzelius is generally credited with the discovery of silicon in 1824. Deville prepared crystalline silicon in 1854, a second allotropic form of the element.
Silicon around us Read more »
Silicon is probably essential in higher plants and perhaps to mammals. Diatoms, some protozoa, some sponges, and some plants use silicon dioxide (SiO2) as a structural material. Silicon is known to be required by chicks and rats for growth and skeletal development. Silicon is not particularly toxic but finely divided silicates or silica cause major damage to lungs.
Silicon is not found free in nature, but occurs chiefly as the oxide, and as silicates. Sand, quartz, rock crystal, amethyst, agate, flint, jasper, and opal are all silicon oxides. Granite, hornblende, asbestos, feldspar, clay, mica are a few of the many silicate minerals. Silicon makes up 25.7% of the earth's crust by weight and is the second most abundant element in the earth's crust. Silicon is present in the sun and stars and is a principal component of a class of meteorites known as aerolites.
| Location | ppb by weight | ppb by atoms | Links |
|---|---|---|---|
| Universe | 700000 | 30000 | 
|
| Crustal rocks | 270000000 | 200000000 | 
|
| Human | 260000 ppb by weight | 58000 atoms relative to C = 1000000 | 
|
Physical properties Read more »
Density of solid: 2330 kg m-3
Molar volume: |196| cm3
Thermal conductivity: |206| W m‑1 K‑1
Heat properties Read more »
Melting point: 1687 [1414 °C (2577 °F)] K
Boiling point: 3173 [2900 °C (5252 °F)] K
Enthalpy of fusion: |203| kJ mol-1
Crystal structure Read more »
The solid state structure of silicon is: diamond.
Silicon: orbital properties Read more »
Silicon atoms have 14 electrons and the shell structure is 2.8.4. The ground state electronic configuration of neutral Silicon is [Ne].3s2.3p2 and the term symbol of Silicon is 3P0.
Pauling electronegativity: 1.90 (Pauling units)
First ionisation energy: 786.5 kJ mol‑1
Second ionisation energy: 1577.1 kJ mol‑1
Isolation
Isolation: there is normally no need to make silicon in the laboratory as it is readily available commercially. Silicon is readily available through the treatment of silica, SiO2, with pure graphite (as coke) in an electric furnace.
SiO2 + 2C → Si + 2CO
Under these conditions, silicon carbide, SiC, can form. However, provided the amount of SiO2 is kept high, silicon carbide may be eliminated.
2SiC + SiO2 → 3Si + 2CO
Very pure silicon can be made by the reaction of SiCl4 with hydrogen, followed by zone refining of the resultant silicon.
SiCl4 + 2H2 → Si + 4HCl
Silicon isotopes Read more »
Silicon isotopes are used in a variety of applications. Si-28 has been suggested to improve the thermal conductivity of semiconductors. Si-29 is used extensively in NMR spectroscopy. Si-30 has been used to produce the radioisotope Si-31. Si-30 has also been used to study the self-diffusivity of Silicon and it has been used to study the isotope effect on superconductivity.
| Isotope | Mass /Da |
Natural abund. (atom %) |
Nuclear spin (I) |
Nuclear magnetic moment (μ/μN) |
|---|---|---|---|---|
| 28Si | 27.9769271 (7) | 92.2297 (7) | 0 | 0 |
| 29Si | 28.9764949 (7) | 4.6832 (5) | 1/2 | -0.55529 |
| 30Si | 29.9737707 (7) | 3.0872 (5) | 0 | 0 |
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