Silicon
Silicon is a chemical element with symbol Si and atomic number 14. It is a tetravalent metalloid, more reactive than germanium, the metalloid directly below it in the table. Controversy about silicon's character dates to its discovery.
Identity
- Atomic mass
- [28.084, 28.086] u
- Category
- Metalloids
- Group
- 14
- Period
- 3
- Block
- p
- Oxidation States
- −4, +2, +4
- Phase (25 °C)
- Solid
- Appearance
- crystalline, reflective with bluish-tinged faces
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p2
- Short configuration
- [Ne] 3s2 3p2
- Electrons per shell
- 2, 8, 4
- Electronegativity (Pauling)
- 1.90
- Electron affinity
- 134 kJ/mol
- 1st ionization energy
- 787 kJ/mol
- Ionization energies
- 787 · 1577 · 3232 · 4356 · 16091… kJ/mol
Physical properties
- Melting point
- 1413.8 °C (1687 K)
- Boiling point
- 3264.8 °C (3538 K)
- Density
- 2.329 g/cm³
- Molar heat capacity
- 19.8 J/(mol·K)
Chemical behavior of silicon
Silicon has four valence electrons ([Ne] 3s² 3p²) and is the archetypal metalloid: semiconductor, neither metal nor non-metal. It almost always acts as +4 in huge tetrahedral covalent networks (silica, silicates, silicones), and as −4 only against very electropositive metals (silicides). Its intermediate electronegativity (1.90) allows it to bond with itself in discrete chains, but its glory is the crystal lattice: ultrapure silicon is the basis of all electronics.
Reactivity
Si + 2 Cl₂ → SiCl₄
With halogens it reacts on heating giving volatile tetrahalides. Silicon tetrachloride is the raw material for purifying electronic silicon by distillation.
Si + O₂ → SiO₂
It burns in oxygen forming silicon dioxide, an extraordinarily stable three-dimensional network. This affinity for oxygen explains why it never appears native and that sand is its natural form.
Si + 2 NaOH + H₂O → Na₂SiO₃ + 2 H₂
Concentrated bases dissolve it releasing hydrogen and giving soluble silicates (soluble glass). It is the chemical attack that engraves chips in the semiconductor industry.
3 SiO₂ + 2 Al → 3 Si + 2 Al₂O₃
Aluminothermy removes oxygen from silica to obtain metallurgical silicon. Electronic silicon requires subsequent purification by zone refining up to purity of nine nines.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Silicon dioxide (silica) | SiO₂ | Sand, glass, quartz and optical fibre |
| Silicones | (R₂SiO)ₙ | Sealants, prosthetics, cosmetics and lubricants |
| Silicon carbide | SiC | Abrasives and power electronics |
| Silicon tetrachloride | SiCl₄ | Electronic silicon purification |
| Sodium silicate | Na₂SiO₃ | Soluble glass, detergents and adhesives |
Electron shell distribution
View in the atom builderIsotopes
Natural silicon mixes three stable isotopes: silicon-28 (²⁸Si, ~92.2%), silicon-29 (~4.7%) and silicon-30 (~3.1%), all with fourteen protons. The atomic mass was calibrated with ultrapure ²⁸Si spheres to redefine the kilogram in 2019.
Occurrence and production
It is the second element in the crust (~28%), after oxygen: sand, quartz, clays and all silicate rocks. It never appears native due to its affinity with oxygen. It is obtained by reduction of pure quartz with coke in an electric furnace, and ultrapurified by the Siemens process for electronics.
History and origin of the name
Jöns Jacob Berzelius isolated impure it in 1824 by reducing potassium fluorosilicate, and Deville obtained the crystalline form in 1854. It takes its name from the Latin silex (flint). For a century it was simply a glass and ceramic material, until the Transistor (1947) and the chip turned it into the element of the digital age.
Applications and relevance of silicon
Uses of the element
Ultrapure silicon forms chip wafers, solar cells and sensors: each phone carries grams of perfect crystal. Metallurgical silicon hardens aluminium alloys for engines and tyres.
Uses of its compounds
Silica makes glass, optical fibre and cement; silicones seal bathrooms, mould prosthetics and style hair; silicon carbide cuts and manages power of electric cars. We live on silicon and talk through it.
Health, safety and environment
Biological role
Plants use it to rigidify stems (rice accumulates up to 10%) and humans need it in traces for bones and collagen. Inhaled crystalline silica dust, however, causes silicosis, a serious and irreversible lung fibrosis.
Safety
Fine silicon dust is combustible and can explode in suspension; crystalline silica in quarries and construction sites requires masks and extraction. Silicone medical devices, on the other hand, are inert and biocompatible.
Environment
Abundant and safe as a material, but manufacturing one kilogram of solar silicon consumes a lot of energy and generates silicon tetrachloride residue. Recycling panels and chips is beginning to close the loop of the digital age.
Frequently asked questions about Silicon
Why is silicon the king of chips?
Because it is a semiconductor: it conducts halfway and its conductivity is dosed with minimal impurities (doping), which allows carving millions of switches in a millimetre. In addition it forms a perfect oxide (SiO₂) that insulates, is abundant in sand and withstands heat. Germanium, his cousin, was used first but has no useful oxide. Without that irrepeable combination there would be no digital age.
Do chips really are made from sand?
Yes, but with extreme refinement: sand (quartz) is reduced to metallurgical silicon, distilled as trichlorosilane, ultrapurified and grown in monocrystals that are cut into mirror-like wafers. The required purity is nine nines: one foreign atom per billion. From the beach to the processor there are months of chemistry and physics. Sand costs cents; perfect crystal, thousands of euros.
Why is optical fibre glass?
Because ultrapure silica is the most transparent material known: a kilometre of modern fibre loses less light than a one-meter window. Laser pulses travel through its interior bouncing without escaping. Each thread, as thin as a hair, carries thousands of calls and films. Without SiO₂ purissima there would be physical internet: the oceans are sewn with sand glass.
What happens to solar panels at the end of their life?
They last 25–30 years and the wave of retirees is already beginning: they contain glass, aluminium and recoverable silicon, in addition to traces of lead and silver. Recycling them today costs more than burying them, but the EU obliges to collect them and new plants already recover 95% of glass and silicon. The cleanest energy must also close its material loop completely.
Is silicon and silicone the same?
No: silicon is the crystalline element of chips; silicones are polymers that combine it with oxygen and carbon, soft and flexible. To confuse them is like confusing the carbon of diamond with plastic. One is precision electronics, the other sealants, prosthetics and cosmetics. Both are born from sand, but take opposite paths: crystalline hardness versus elasticity.
What is silicosis and who suffers?
An incurable lung fibrosis caused by breathing crystalline silica dust for years: miners, bricklayers, sandblasters and masons without protection. The particles scar the lung until it suffocates. It is one of the oldest and still kills thousands of people each year where there are no masks or cutting water. Prevention costs cents; to cure it is impossible. The dust of stone is the invisible enemy.
Can silicon replace carbon in life?
No in practice: although it is his group cousin, its bonds with itself are weaker and its oxide is a solid rock, not a gas expelled like CO₂. Life needs stable chains and volatile waste, exactly what carbon offers and silicon denies. Silicon aliens remain in science fiction. Biochemistry chose well: carbon is irreplaceable.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.