Silicon Si

Discovery

Silica, silicon dioxide, has been used since prehistoric times in the form of flint tools, and later to make glass and pottery. Antoine Lavoisier suspected in 1787 that silica was the oxide of an undiscovered element, and Humphry Davy tried and failed to break it down.

Joseph Louis Gay-Lussac and Louis Jacques Thénard may have produced impure amorphous silicon in 1811, but the discovery is generally credited to the Swedish chemist Jöns Jacob Berzelius, who in 1824 heated potassium fluorosilicate with potassium and purified the product to obtain amorphous silicon. Crystalline silicon was first prepared in 1854 by Henri Sainte-Claire Deville.

Silicon's modern importance began in the mid-twentieth century. Methods for growing large single crystals and for zone refining allowed silicon to replace germanium in transistors, and the first silicon integrated circuits appeared around 1960.

Origin of the name

The name comes from the Latin silex (genitive silicis), meaning flint. Berzelius called it silicium; the Scottish chemist Thomas Thomson proposed silicon in 1817, using the '-on' ending of boron and carbon to reflect its non-metallic character. The symbol is Si. Silicon should not be confused with silicone, a family of polymers that contain silicon, oxygen and carbon.

Main uses

• Electronics: chips are made from silicon wafers purified to more than 99.9999999 percent.
• Solar energy: most photovoltaic panels use crystalline silicon cells.
• Alloys: ferrosilicon is added in steelmaking, and aluminium–silicon alloys are cast into engine parts.
• Construction and glass: silica is the main ingredient of glass, concrete, cement and ceramics.
• Silicones: silicon is the starting point for silicone sealants, lubricants and rubbers.

Isotopes

Silicon has three stable isotopes: silicon-28 (about 92.2 percent), silicon-29 (about 4.7 percent) and silicon-30 (about 3.1 percent). Silicon-29 is used in NMR studies of glasses and minerals. Nearly perfect spheres of isotopically enriched silicon-28 were used to count atoms precisely and determine the Avogadro constant, part of the work behind the 2019 redefinition of the kilogram. Silicon's radioactive isotopes have no widespread applications.

In everyday life

Sand, quartz, granite and clay are all rich in silicon, which makes up roughly 28 percent of the crust by mass. Diatoms and some plants build skeletons and structures from silica.

Breathing fine crystalline silica dust over many years, for example in quarrying, stone cutting or sandblasting, can cause silicosis, a serious lung disease, so dust control is important in these jobs.