Silicon

Silicon is the element inside every computer chip, smartphone and solar panel. It is the second most abundant element in the Earth's crust, forms the basis of all our glass and most concrete, and has become so associated with technology that the world's biggest tech hub, Silicon Valley, is named after it.

  • Atomic Number1414 protons, 14 electrons
  • Atomic Mass28.085 uAbout 28× heavier than hydrogen
  • State at Room TempSolidshiny blue-grey solid
  • Density2.3296 g/cm³Slightly denser than aluminium
  • Melting / Boiling1413.8°C / 3264.8°CMelts at a high 1,414°C
  • Discovered1854Jöns Jacob Berzelius, 1824

How does silicon's mass compare to nearby elements?

Silicon sits close to the midpoint between hydrogen and iron on the atomic mass scale.

Atomic Mass Comparison
Aluminium27 u
Silicon28 u
Phosphorus31 u
Sulfur32 u
Iron56 u

Silicon at 28 atomic mass units sits almost exactly halfway between carbon (12 u) and iron (56 u). Like carbon, it forms four bonds, but silicon's bonds are weaker, which is why silicon chemistry is so different from carbon chemistry.

What is silicon?

Silicon is a metalloid in Group 14 of the periodic table, sitting directly below carbon. It has 14 protons and four electrons in its outer shell, just like carbon. Like carbon, it can bond to four other atoms at once. But silicon atoms are larger and their bonds weaker, so silicon does not form the enormous chains and rings that make carbon chemistry so rich. Instead, silicon forms a giant lattice with oxygen, silicon dioxide, the main component of sand, quartz and most rocks.

Silicon gets its name from the Latin silex or silicis, meaning flint. Flint is a hard form of silicon dioxide that ancient humans used to make arrowheads, axes and fire-starting tools. Jöns Jacob Berzelius, who isolated silicon in 1824, chose the name because flint was the most familiar silicon material of his time.

Fact About 25% of the Earth's crust by weight is silicon, but you will never find it lying around as a shiny metal. All of it is locked inside compounds with oxygen and other elements. The perfectly pure silicon needed for computer chips must be grown as giant single crystals in specially controlled furnaces in ultra-clean rooms.

Where you find silicon

In space

Silicon is one of the ten most abundant elements in the universe. Together with oxygen it makes up the main minerals of rocky planets. Mars, the Moon and all the inner rocky planets are largely silicate rock. The mineral olivine (magnesium-iron silicate) is one of the most common minerals found in meteorites.

On Earth

Silicon is everywhere. The crust is approx. 28% silicon by mass: second only to oxygen. Almost all common rocks are silicon compounds.

  • Sand and quartz. Silicon dioxide (SiO₂) is the main component of beach sand, desert sand and the mineral quartz. Sand is essentially crushed silicate rock.
  • Silicate minerals. Feldspar, mica, olivine, clay and most common rock-forming minerals are silicates. The Earth's crust is essentially one giant silicate rock.
  • Pure silicon production. Ultra-pure silicon does not occur naturally. It is made by purifying quartz sand through a series of chemical reactions, producing silicon with fewer than one impurity atom per billion.

How we use silicon

  • Computer chips. Almost all microprocessors, memory chips and solar cells are made from ultra-pure silicon. A single chip the size of a fingernail can contain more than 15 billion transistors.
  • Glass. Most glass is melted silicon dioxide, sand. Different metal oxides produce different colours and properties, from the iron-tinted green of bottle glass to the clear borosilicate of laboratory equipment.
  • Concrete and cement. Calcium silicate compounds are the main binding agents in cement. Concrete: the most widely used construction material in the world, is based on silicon chemistry.
  • Solar panels. Silicon solar cells convert sunlight directly into electricity. Silicon is ideal because it absorbs light well and electrons can move through it efficiently when freed by photons.
Did you know? Silicon Valley in California gets its name from the silicon semiconductor industry that grew there from the 1950s. The name was coined by journalist Don Hoefler in 1971. Today it is home to Apple, Google, Meta, Intel and hundreds of other technology companies, all built on silicon chemistry.

How it was discovered

Silicon dioxide (silica) was known as a distinct substance by the 18th century, but isolating the element itself took longer. In 1811, Gay-Lussac and Thénard in Paris produced impure amorphous silicon. In 1824, the Swedish chemist Jöns Jacob Berzelius is credited with obtaining relatively pure silicon by heating potassium fluorosilicate with potassium metal. Crystalline silicon, far more useful for electronics, was first produced by Henri Deville in 1854.

Deeper dive: semiconductors and the silicon chip revolution

Pure silicon is a semiconductor: it conducts electricity better than an insulator like rubber, but not as well as a metal like copper. This intermediate conductivity can be precisely controlled by doping, adding tiny amounts of other elements. Adding phosphorus gives extra free electrons (n-type silicon). Adding boron creates electron "holes" (p-type silicon). Where n-type and p-type meet, you get a p-n junction: the fundamental building block of every transistor, solar cell and LED.

The transistor was invented in 1947 and has become the most manufactured object in human history. A modern smartphone processor contains more than 15 billion transistors, each one smaller than a virus. They switch on and off billions of times per second, performing all the calculations that run your apps and send your messages.

Silicon wafers for electronics must be 99.9999999% pure, nine nines. A single impurity atom per billion silicon atoms can ruin a chip. Achieving this requires multiple stages of chemical purification and crystal growth in "clean rooms" where workers wear full suits to prevent a stray hair from contaminating the silicon. The largest silicon wafers used today are 300 mm (approx. 12 inches) across and contain thousands of chips.

Silicon is the foundation of both the natural world and modern technology, from beach sand to supercomputers. Moving to 15 protons brings us to phosphorus, an element discovered in one of chemistry's most bizarre experiments.