Silicon

Silicon sits directly below carbon in group 14 and also forms four bonds ([Ne]3s2 3p2), but its larger atom changes the chemistry. Silicon-silicon bonds are relatively weak and silicon rarely forms stable double bonds, while the silicon-oxygen bond is very strong. As a result, silicon in nature is almost always bonded to oxygen, in SiO4 tetrahedra that link into quartz and the silicate minerals making up most of Earth's crust. Silicon is the second most abundant element in the crust, about 28% by mass.

Pure silicon crystallizes in the same structure as diamond and is a semiconductor with a band gap of 1.12 eV: it conducts poorly when pure, but adding a few atoms of boron or phosphorus per million creates p-type or n-type material whose conductivity can be precisely controlled. Junctions between these regions form diodes, transistors and solar cells. Chip-grade silicon is purified to at least 99.9999999% and grown into large single crystals by the Czochralski method. Far larger quantities of less pure silicon go into aluminium alloys and silicone polymers.

Discovery

Antoine Lavoisier suspected in 1787 that silica was the oxide of an undiscovered element. Joseph Louis Gay-Lussac and Louis Jacques Thénard made impure amorphous silicon in 1811, but Jöns Jacob Berzelius is usually credited with its discovery in 1823, after heating potassium with potassium fluorosilicate and purifying the product. Henri Sainte-Claire Deville prepared crystalline silicon in 1854. The name was proposed by Thomas Thomson in 1817, from the Latin silex, flint, with an ending matching carbon and boron.