Silicon

Silicon is the chemical element with atomic number 14 and the symbol Si. It is a hard, brittle metalloid in group 14 of the periodic table, and it is the second most abundant element in the Earth’s crust after oxygen. Pure silicon is the basis of modern electronics, and compounds of silicon make up most of the rocks, sand and clay on the planet.

History of silicon

People used silicon compounds long before they knew the element existed. Flint, a form of silica, supplied some of the first tools, and ancient civilizations melted sand to make glass. The name comes from the Latin silex, or silicis, meaning flint.

Early chemists showed little interest in the element despite its abundance. Attempts to break silica apart by electrolysis failed. In 1811 Joseph Louis Gay-Lussac and Louis Jacques Thénard heated silicon tetrachloride with potassium and made a very impure form of silicon, but they did not identify it as a new element.

The credit for the discovery usually goes to the Swedish chemist Jöns Jacob Berzelius. In 1824 he heated potassium fluorosilicate with potassium and washed away the unwanted potassium silicide with water. This left a relatively pure silicon powder. The Royal Society of Chemistry gives 1824 and Berzelius as the date and discoverer.

Properties of silicon

Silicon has a standard atomic weight of about 28.085, which IUPAC gives as an interval because natural samples vary slightly. Its electron configuration is [Ne] 3s2 3p2, so each atom has four outer electrons and typically forms four bonds. PubChem lists an electronegativity of 1.9 and a first ionization energy of 8.152 electronvolts.

Silicon melts at about 1,414 degrees Celsius and boils at about 3,265 degrees Celsius. Its density is 2.3296 grams per cubic centimeter. Ultrapure silicon is a solid with a blue-gray metallic sheen, and it forms a crystal in which every atom is bonded to four neighbors, the same arrangement found in diamond.

Silicon is a semiconductor, meaning that its ability to carry electric current sits between that of a metal and that of an insulator. Adding very small amounts of other elements changes this ability in a controlled way. A semiconductor of this kind can switch current on and off, which is the property that electronic circuits depend on.

Occurrence and production of silicon

Silicon makes up about 27.7 percent of the Earth’s crust by mass. It never occurs as a free element in nature. Instead it is found as silicon dioxide, which includes sand, quartz, flint, agate and opal, and as silicates such as granite, feldspar, mica and clay. Most of the silicon in the crust is bonded to oxygen.

Commercial silicon is made by heating sand with carbon in an electric furnace, which removes the oxygen. The result is metallurgical-grade silicon, used mainly in alloys. For electronics the metal must be purified much further. High-purity silicon is prepared by thermally decomposing ultrapure trichlorosilane gas, and the product is then grown into large single crystals and sliced into thin wafers.

Silicon also appears in biology. Diatoms, which are photosynthesizing algae, build their cell walls from hydrated silica. Many plants form tiny silica particles called phytoliths, which resist decay and survive in fossils, giving researchers evidence of ancient plant life.

Uses of silicon

Most silicon is used in alloys. Aluminum-silicon and iron-silicon alloys go into engine blocks, cylinder heads, machine tools, and the plates of transformers and dynamos, and silicon is also added to deoxidize steel. An alloy is a metallic mixture, and these particular alloys are valued for their strength and the ease with which they can be cast.

In electronics, hyperpure silicon wafers are the foundation of transistors and the integrated circuit, as well as most solar cells. Manufacturers dope the wafers with tiny amounts of boron, gallium, phosphorus or arsenic to control their electrical behavior. This is the reason that a region of the western United States was nicknamed Silicon Valley.

Silicon compounds have many other applications. Sand is the main ingredient of glass, and sand and clay are used to make cement and concrete. Silicates feature in pottery, enamels and ceramics that can withstand high temperatures, while silicon carbide is an important abrasive and is also used in lasers.

Silicones are a different matter. These are polymers with a backbone of alternating silicon and oxygen atoms and methyl groups attached. Silicone oil is a lubricant and an ingredient in some cosmetics, and silicone rubber is a waterproof sealant for windows, pipes and roofs. The word silicone should not be confused with silicon.

Isotopes of silicon

Silicon has three stable isotopes: silicon-28, silicon-29 and silicon-30. Silicon-28 is by far the most common, at roughly 92 percent of natural silicon, while silicon-29 makes up about 4.7 percent and silicon-30 about 3.1 percent. Together they give the atomic weight of about 28.085.

Researchers have used crystals of nearly pure silicon-28 to make almost perfect spheres. By counting the atoms in these spheres, metrologists improved the measurement of the Avogadro constant, which helped to redefine the kilogram in 2019. Silicon-29 is useful in nuclear magnetic resonance studies because, unlike silicon-28, its nucleus has a magnetic moment.

Health and environmental effects of silicon

Silicon is essential to plant life, although its role in animal cells is uncertain. Elemental silicon and pure silica are not toxic. However, breathing dust that contains crystalline silica over many years can cause silicosis, a serious lung disease that affects miners, stonecutters and other workers who are exposed to siliceous dust. Some silicate minerals, including asbestos, are carcinogenic.

Silicon production uses large amounts of electricity, and electronics manufacturing depends on very pure chemicals and water. Information here is general background rather than health advice.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue