Silicon (Si)

Discovery & history

Discovered: 1823 · Jöns Jacob Berzelius

Owing to the abundance of silicon in the Earth's crust, natural silicon-based materials have been used for thousands of years. Silicon rock crystals were familiar to various ancient civilizations, such as the predynastic Egyptians who used them for beads and small vases, as well as the ancient Chinese. Glass containing silica was manufactured by the Egyptians since at least 1500 BC, as well as by the ancient Phoenicians. Natural silicate compounds were also used in various types of mortar for construction of early human dwellings.

Uses & applications

Crystalline bulk silicon is rather inert, but becomes more reactive at high temperatures. Like its neighbour aluminium, silicon forms a thin, continuous surface layer of silicon dioxide (SiO2) that protects the material beneath from oxidation. Because of this, silicon does not measurably react with the air below 900 °C. Between 950 °C and 1160 °C, the formation rate of the vitreous dioxide rapidly increases, and when 1400 °C is reached, atmospheric nitrogen also reacts to give the nitrides SiN and Si3N4. Silicon reacts with gaseous sulfur at 600 °C and gaseous phosphorus at 1000 °C. This oxide layer nevertheless does not prevent reaction with the halogens; fluorine attacks silicon vigorously at room temperature, chlorine does so at about 300 °C, and bromine and iodine at about 500 °C. Silicon does not react with most aqueous acids, but is oxidised and complexed by hydrofluoric acid mixtu

Isotopes

Naturally occurring silicon is composed of three stable isotopes, 28Si (92.24%), 29Si (4.67%), and 30Si (3.07%). Out of these, only the odd 29Si is of use in NMR and EPR spectroscopy, and it has nuclear spin (I =⁠1/2⁠). All three are produced in Type Ia supernovae through the oxygen-burning process, with 28Si being made as part of the alpha process and hence the most abundant. The fusion of 28Si with alpha particles by photodisintegration rearrangement in stars is known as the silicon-burning process; it is the last stage of stellar nucleosynthesis before the rapid collapse and violent explosion of the star in question in a type II supernova. Twenty-two radioisotopes have been characterized, the two stablest being 32Si with a half-life of about 157 years, and 31Si with a half-life of 2.62 hours. All the remaining radioactive isotopes have half-lives that are less than seven seconds, and