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Silicon (Si)

Silicon (symbol Si) is the chemical element with atomic number 14: a metalloid, solid at 0 °C, with an atomic mass of 28.085 u. Discovered in 1824 (Jöns Jacob Berzelius).

Silicon is the second most abundant element in Earth's crust: sand, quartz and most rocks are made of it. Purified to the extreme, it becomes a semiconductor, a material whose electrical conduction can be finely controlled, the basis of every microprocessor and solar panel. Not to be confused with silicones, the flexible polymers that contain it.

Key facts

Atomic number
14
Symbol
Si
French name
Silicium
Atomic mass
28.085 u
Molar mass
28.085 g/mol
Family
Metalloids
Position
period 3, group 14, p-block
State at 0 °C
Solid
Melting point
1,413.9 °C
Boiling point
3,264.9 °C
Density
2.33 g/cm³
Electronegativity (Pauling)
1.9
First ionization energy
787 kJ/mol
Atomic radius
110 pm
Electron configuration
[Ne] 3s² 3p²
Abundance in Earth's crust
282,000 ppm (2nd most abundant element)
Indicative price
2 $/kg (order of magnitude)
Radioactive
no
Discovery
1824, Jöns Jacob Berzelius

Origin of the name

From the Latin silex, flint or pebble.

What does silicon look like?

A dark gray solid with a bluish metallic sheen, hard but as brittle as glass.

Where is silicon found?

About 28% of the mass of Earth's crust, always bound to oxygen in silica (quartz) and silicates. It is rarely found pure in nature.

Natural sources

  • Quartz
  • Feldspars
  • Micas
  • Olivine
  • Clays

How is silicon produced?

Very pure quartz is reduced with carbon in electric furnaces at around 2,000 °C. Electronic-grade silicon is then purified to 99.9999999% (“nine nines”) and grown into large single-crystal ingots. World production, including ferrosilicon, is close to 9 million tonnes a year, about 70% of it in China.

Top producers

  • China
  • Russia
  • Brazil
  • Norway

What is silicon used for?

  • Microchips and microprocessors.
  • Photovoltaic cells in solar panels.
  • Aluminium-silicon alloys for cast parts (engines).
  • Silicones (seals, kitchenware, implants).
  • Glass, cement and ceramics (as silica).

In everyday life

  • The processor in your phone
  • Rooftop solar panels
  • A silicone cake mold
  • Windowpanes (glass made from sand)

Role in living things

Diatoms, microscopic algae, build shells of glass (silica), as do glass sponges. Horsetails and rice accumulate it to strengthen their stems. In humans it is present in traces, possibly playing a role in bone and connective tissue.

Hazards of silicon

Pure silicon is of low toxicity. However, prolonged inhalation of crystalline silica dust (quarries, construction sites, cutting quartz countertops) causes silicosis, a serious and irreversible lung disease.

Cosmic origin

  • Supernovae: Forged in the cores of massive stars, then scattered when they explode.
  • White dwarfs: Produced by the thermonuclear explosion of a white dwarf (type Ia supernova).

History of silicon

As early as 1787, Lavoisier suspected that silica was the oxide of an unknown element. The Swede Jöns Jacob Berzelius isolated silicon in 1824. In 1954, Bell Labs created the first silicon solar cell, and the silicon transistor ushered in the age of microelectronics.

Did you know?

  • A modern processor contains tens of billions of transistors etched into a silicon wafer.
  • “Silicon” is the element and “silicone” the polymer: Silicon Valley has nothing to do with implants.
  • Silicon-based life, a science fiction favorite, is considered unlikely because its bonds are less varied and less stable than carbon's.

Isotopes of silicon

Three stable isotopes, with silicon-28 making up over 92% of the total. Spheres of almost pure silicon-28 helped redefine the kilogram and the mole.

  • silicon-28: 92.223% of natural silicon, stable. Ultra-pure spheres let scientists count atoms to redefine the mole (2019).
  • silicon-29: 4.685% of natural silicon, stable. The only stable silicon isotope visible in NMR.
  • silicon-30: 3.092% of natural silicon, stable
  • silicon-31: radioactive, half-life 2.62 h. Made by neutron irradiation, it turns into phosphorus, evenly doping the silicon in power electronics.
  • silicon-32: radioactive, half-life 153 years. Cosmogenic isotope used to date recent sediments and ice (a few centuries old).

Common compounds

Quartz (sand) (SiO₂) · Silicon carbide (SiC)

Related elements

Same family (metalloids): Boron (B), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te).

Same column (group 14): Carbon (C), Germanium (Ge), Tin (Sn), Lead (Pb), Flerovium (Fl).