Silicon (Si)

Stable isotopes of silicon available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Si-28 14 14 27.9769265 92.23% 99.90-99.99% Elemental
Si-28 14 14 27.9769265 92.23% 99.90-99.99% Oxide
Si-29 14 15 28.9764947 4.67% >99.00% Elemental
Si-29 14 15 28.9764947 4.67% >99.00% Oxide
Si-30 14 16 29.9737702 3.10% >99.00% Elemental
Si-30 14 16 29.9737702 3.10% >99.00% Oxide

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The discovery of silicon is credited to Jöns Jakob Berzelius in 1824 in Sweden. Its name originates with the Latin word silicis, which means “flint.” It is the second most abundant element, exceeded only by oxygen, making up 25.7% of the earth's crust by weight.

Silicon exists in two allotropic modifications: Crystalline silicon is made up of grayish-black lustrous needle-like crystals, or octahedral platelets, with a cubic structure. Amorphous silicon is a brown powder. Elemental silicon is relatively stable in most substances at ordinary temperatures and shows similarity to other elements of its group. It exists as sand quartz, flint, amethyst, agate, opal, jasper and rock crystal.

Silicates and silica have many applications in numerous fields, including making cements and concretes for building materials, glasses and glassware, ceramics, pigments, adsorbents, paper boards, fillers, detergents, precious gems, catalysts and water-softeners. Silicones are used as lubricants and in making rubbers, plastics, electrical coatings, adhesives, paints and varnishes, and as water repellents for textiles, papers and concrete. Elemental silicon has a major application in computer chips. Silicon of hyperpurity — doped with trace elements, such as boron, phosphorus, arsenic or gallium — is one of the best semiconductors and is used in transistors, power rectifiers, diodes and solar cells. Hydrogenated amorphous silicon converts solar energy into electricity.

Inhalation of silica dusts or silicate mineral dusts can cause silicosis or other lung diseases.

Properties of Silicon

Name Silicon
Symbol Si
Atomic number 14
Atomic weight 28.08555
Standard state Solid at 298 °K
CAS Registry ID 7440-21-3
Group in periodic table 14 
Group name None 
Period in periodic table
Block in periodic table p-block 
Color Dark gray with a bluish tinge
Classification Semi-metallic
Melting point 1414 °C
Boiling point 2355 °C
Thermal conductivity 149 W/(m·K) at 298.2 °K
Electrical resistivity 3-4 µΩ·cm at 0 °C
Electronegativity 1.80
Specific heat 0.71 kJ/kg K
Heat of vaporization 359 kJ·mol-1
Heat of fusion 50.2 kJ·mol-1
Density of high-purity liquid 2.53 g/cm3 at 1414 °C
Density of solid 2.33 g/cm3
Electron configuration [Ne]3s23p2
Atomic radius 1.173 Å
Oxidation state +4
Critical temperature 4 °C
Calculated crucial pressure 530 atm

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