Silicon

Silicon sits at spot 14 on the periodic table, marked by the symbol Si. This element appears as a hard, brittle crystal with a blue-grey metallic shine. It behaves as a tetravalent non-metal—sometimes grouped with metalloids—and acts as a semiconductor. In group 14, carbon lies above it, while germanium, tin, lead, and flerovium fall below. Silicon is largely unreactive. It plays a vital role in plant biology, supporting several physiological and metabolic processes. In technology, it is the go-to semiconductor for transistors, solar cells, and integrated circuits, dominating this field because of its low cost, strong electronic properties, and adaptable physical traits.

Because silicon bonds so tightly with oxygen, isolating it in pure form took until 1823, when Jöns Jakob Berzelius finally succeeded. Its oxides form a family of anions called silicates. Silicon melts at 1414 °C and boils at 3265 °C—the second highest melting and boiling points among all metalloids and nonmetals, beaten only by boron.

By mass, silicon is the eighth most common element in the universe, yet it rarely appears pure in Earth's crust. It is widespread through space in cosmic dust, planetoids, and planets as silicon dioxide (silica) or silicates. Over 90% of Earth's crust consists of silicate minerals, making silicon the second most abundant element in the crust at about 28% by mass, after oxygen.

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

The late 20th century through the early 21st century is often called the Silicon Age (also the Digital Age or Information Age), due to the massive impact of elemental silicon on the modern world economy. A small fraction of highly purified silicon—less than 15%—goes into semiconductor electronics, which is essential for the transistors and integrated circuit chips in most modern technology, including smartphones and other computers. In 2019, 32.4% of the semiconductor market was for networks and communications devices, and the industry is projected to reach $726.73 billion by 2027.

Silicon is essential in biology. Most animals need only traces, but some sea sponges and microorganisms—like diatoms and radiolaria—secrete skeletal structures made of silica. Silica is also deposited in many plant tissues.

**History** Because silicon is so abundant in Earth's crust, natural silicon-based materials have been used for thousands of years. Ancient civilizations, including predynastic Egyptians and the ancient Chinese, were familiar with silicon rock crystals, using them for beads and small vases. Egyptians manufactured glass containing silica as early as 1500 BC, as did the ancient Phoenicians. Natural silicate compounds were also used in various mortars for early human dwellings.

**Discovery** In 1787, Antoine Lavoisier suspected that silica might be an oxide of a fundamental element, but silicon's strong affinity for oxygen prevented him from reducing the oxide and isolating the element. In 1808, after an attempt to isolate silicon, Sir Humphry Davy proposed the name "silicium," from the Latin *silex*, *silicis* for flint, adding the "-ium" ending because he believed it to be a metal. Most other languages use transliterated forms of Davy's name, sometimes adapted to local phonology (e.g., German *Silizium*, Turkish *silisyum*, Catalan *silici*, Armenian *Սիլիցիում* or *Silitzioum*). A few others use a calque of the Latin root (e.g., Russian *кремний*, from *кремень* "flint"; Greek *πυρίτιο* from *πυρ* "fire"; Finnish *pii* from *piikivi* "flint"; Czech *křemík* from *křemen* "quartz," "flint").

Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon in 1811 by heating recently isolated potassium metal with silicon tetrafluoride, but they did not purify or characterize the product, nor identify it as a new element. Silicon received its present name in 1817 from Scottish chemist Thomas Thomson. He kept part of Davy's name but added "-on" because he believed silicon was a nonmetal similar to boron and carbon. In 1824, Jöns Jacob Berzelius prepared amorphous silicon using roughly the same method as Gay-Lussac (reducing potassium fluorosilicate with molten potassium metal), purifying the product to a brown powder by repeated washing. He is usually credited with the element's discovery. That same year, Berzelius became the first to prepare silicon tetrachloride (SiCl₄); silicon tetrafluoride had already been prepared in 1771 by Carl Wilhelm Scheele by dissolving silica in hydrofluoric acid. In 1846, J. Von Ebelman synthesized tetraethyl orthosilicate (Si(OC₂H₅)₄).

Silicon in its more common crystalline form was not prepared until 31 years later, by Deville. Passing silicon chloride vapors over pure aluminum produced pure, hard octahedral crystals. Friedrich Wöhler discovered the first volatile hydrides of silicon, synthesizing trichlorosilane in 1857 and silane itself in 1858, but a detailed investigation of the silanes was only completed later.