Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic table: carbon is above it; and germanium, tin, lead, and flerovium are below it. It is relatively unreactive.

Because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Its oxides form a family of anions known as silicates. Its melting and boiling points of 1414 °C and 3265 °C, respectively, are the second highest among all the metalloids and nonmetals, being surpassed only by boron.

Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earth's crust. It is widely distributed in space in cosmic dusts, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass), after oxygen.

Most silicon is used commercially without being separated, often with very little processing of the natural minerals. Such use includes industrial construction with clays, silica sand, and stone. Silicates are used in Portland cement for mortar and stucco, and mixed with silica sand and gravel to make concrete for walkways, foundations, and roads. They are also used in whiteware ceramics such as porcelain, and in traditional silicate-based soda–lime glass and many other specialty glasses. Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Silicon is the basis of the widely used synthetic polymers called silicones.

The late 20th century to early 21st century has been described as the Silicon Age (also known as the Digital Age or Information Age) because of the large impact that elemental silicon has on the modern world economy. The small portion of very highly purified elemental silicon used in semiconductor electronics (<15%) is essential to the transistors and integrated circuit chips used in most modern technology such as smartphones and other computers. In 2019, 32. 4% of the semiconductor market segment was for networks and communications devices, and the semiconductors industry is projected to reach $726. 73 billion by 2027. Silicon is an essential element in biology. Only traces are required by most animals, but some sea sponges and microorganisms, such as diatoms and radiolaria, secrete skeletal structures made of silica. Silica is deposited in many plant tissues.

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Atomic properties

Standard atomic weight28.085 ±0.001 [28.084 … 28.086]
Atomic mass28.0852 u

Atomic radii

Radius (empirical)111 pm
Radius (calculated)111 pm
Covalent radius111 pm
Van der Waals radius210 pm

Atomic shell

Electron configurationNe 3s2 3p2
Ionization energy(1st) 8.15168 eV
(2nd) 16.34585 eV
(3rd) 33.493 eV
(4th) 45.14179 eV
(5th) 166.767 eV
Shell model

Physical properties

Density2.336 g·cm−3 (293.1 K)
Molar volume1.206·10-5 m3·mol−1
Speed of sound8,433 m·s−1 (293 K)


Melting point1,687 K
Boiling point3,538 K
Liquid range1,851 K
Transition temperature8.5 K


Melting enthalpy50.2 kJ·mol-1
Enthalpy of vaporization359 kJ·mol-1
Binding energy456 kJ·mol-1

Heat and conductivity

Specific heat capacity703 J·kg−1·K−1 (298 K)
Thermal conductivity150 W·m-1·K-1
Expansion coefficient2.6·10-6 K-1


Mohs hardness6.5

Elastic properties

Young’s modulus47 GPa
Bulk modulus100 GPa

Electrical properties

Electrical conductivity5·10-4 S·m-1
Resistance0.001 Ωm


Magnetic susceptibility-3.9·10-6 cm3·mol−1 (298 K)

Optical properties

Reflectivity28 %

Chemical properties

Oxidation state-4, (2), +4


Pauling scale1.9
Sanderson scale2.14
Allred-Rochow scale1.74
Mulliken scale2.28
Allen scale1.916
Ghosh-Gupta scale5.523 eV
Boyd-Edgecombe scale1.87
Nagle scale1.87
Pearson absolute negativity4.77 eV

Other properties

Natural occurrenceprimordial
Crystal structureDiamond structure
Goldschmidt Classificationlithophile
Superconductorwith transition tempperature under special conditions
Price/kg1.7 USD

Natural abundances

700,000 ppb ≈ 7.03·1015 M☉
900,000 ppb ≈ 1.79·1015 Mt
1.4·108 ppb ≈ 140 kg
Earth’s crust
2.7·108 ppb ≈ 7.47·109 Mt
1,000 ppb ≈ 1.37 Mt
Flowing water
5,000 ppb ≈ 80 Gt
Human body
260,000 ppb ≈ 18.1 g