14 Si 28.085

Silicon

Metalloid Silicium solid

[Ne] 3s² 3p² · 2 · 8 · 4

← Al Aluminium P Phosphorus →

The second most abundant element in the crust and the material the whole digital world stands on. Silicon is a semiconductor whose conductivity a trace dopant can swing by ten orders of magnitude, and that property is what made the transistor possible.

3D model

Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.

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Atomic properties

Atomic number: 14
Atomic mass: 28.085 а.е.м.
Electron configuration: [Ne] 3s² 3p²
Electrons per shell: 2 · 8 · 4
Block: p-block
Group: Carbon group
Period: 3
Electronegativity (Pauling): 1.9
Electronegativity (Allen): 1.92
Atomic radius: 111 pm
Covalent radius: 111 pm
Van der Waals radius: 210 pm
Ionisation energy 1: 786.5 kJ/mol
Ionisation energy 2: 1 577.1 kJ/mol
Ionisation energy 3: 3 231.6 kJ/mol
Ionisation energy 4: 4 355.5 kJ/mol
Ionisation energy 5: 16 091 kJ/mol
Electron affinity: 134.1 kJ/mol
Common oxidation states: +4
Oxidation states: -4, -3, -2, -1, +1, +2, +3, +4

Physical properties

State at 25 °C: solid
Density: 2.329 g/cm³
Melting point: 1 687 K · 1 413.9 °C
Boiling point: 3 538 K · 3 264.9 °C
Speed of sound: 8 433 m/s

Thermal properties

Heat of fusion: 50.21 kJ/mol
Heat of vaporisation: 383 kJ/mol
Specific heat capacity: 0.705 J/(g·K)
Thermal conductivity: 149 W/(m·K)

Mechanical properties

Young's modulus: 130 GPa
Shear modulus: 51 GPa
Bulk modulus: 100 GPa
Poisson ratio: 0.28
Mohs hardness: 6.5
Brinell hardness: no data

Electrical and magnetic properties

Electrical resistivity: 6.4·10⁸ nΩ·m
Magnetic ordering: diamagnetic
Curie point: no data
Néel point: no data
Superconducting point: no data

Crystal structure

Crystal structure: diamond cubic
Lattice constants: a = 543.09 pm

Abundance

In the crust: 282 000 mg/kg
In the ocean: 2.2 mg/L
In the universe: 700 000 mg/kg
In the human body: 260 mg/kg

Isotopes

Isotope	Abundance	Half-life	Decay mode
²⁸Si	92.223 %	stable	—
²⁹Si	4.685 %	stable	—
³⁰Si	3.092 %	stable	—

Silicon-28 matters enough to metrology that a sphere of nearly pure ²⁸Si was used in redefining the kilogram through the Avogadro constant.

Discovery

Year of discovery: 1823
Discovered by: Jöns Jacob Berzelius
Where: Sweden
Origin of the name: from Latin silex (flint)

History

Berzelius obtained amorphous silicon in 1823 by reducing the fluoride with potassium. Growing crystalline silicon had to wait until the 1950s, when the Czochralski method produced single crystals of the needed purity.

Where it occurs

28 % of the crust by mass. Essentially all terrestrial silicon is bound to oxygen: quartz, feldspars, clays and sand are all silicates.

How it is produced

Carbothermic reduction of quartz in an arc furnace gives metallurgical silicon; trichlorosilane and the Siemens process then yield polysilicon at 99.9999999 % purity.

Role in living things

Diatoms build their shells from silica, and horsetails and grasses stiffen their tissue with it. For humans the role is debated: silicon is present in connective tissue, but necessity is unproven.

Safety

Silicon itself is non-toxic. Crystalline silica dust is not: prolonged inhalation causes silicosis, one of the oldest occupational diseases on record.

Uses

Chips and solar cells — the substrate of nearly all electronics
Electrical steel for transformers and motors
Silicones: sealants, lubricants, medical implants
Fused quartz and optical fibre
Ferrosilicon as a deoxidiser in steelmaking

Curiosities

Silicon Valley is named for the substrate material, not for a valley of anything.
A silicon boule for chipmaking is among the purest materials humans make: no more than one foreign atom per billion.
Sand, glass, concrete and a CPU are all the same element.
Silicon is tetravalent like carbon, but Si–Si bonds are too weak for long chains — which is likely why silicon-based life does not exist.