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Revision as of 15:48, 17 December 2018
Silicon (periodic table symbol: Si14) is a chemical element that can be found in several minerals on Mars.
Contents
Chemistry
As a group 14 element, silicon has a chemsitry similar to that of tin and lead, and especially that of carbon and germanium.
As we go down from carbon at the top of group 14, the reactivity (and electropositivity) of the elements increases. At the same time, the bond enthalpy decreases for chains of the element[1]. That is, C-C bonds are more stable than Si-Si bonds, which are more stable than Ge-Ge bonds, etc. The strength of their bonds with hydrogen similarly decreases. This is why, for example, methane is more stable than silane.
Despite the instability of silicon chains relative to their carbon analogues, they are industrially significant.
Silanes
The silanes are acyclic chains of singly-bonded silicon atoms analogous to the alkanes. The cyclosilanes are (highly unstable) cyclic silanes.
Silenes
The silenes are acyclic chains of doubly-bonded silicon atoms, analogous to the alkenes.
Siloxanes
Due to the instability of Si-Si bonds, longer chains of silicon atoms are often constructed with some other atom between the silicon atoms, which bonds more strongly to them. In the case of the siloxanes, this results in Si-O-Si chains. For comparison, the enthalpy of a Si-O bond is in higher than that of a C-C single bond but lower than that of a C=C double bond, and more than twice that of a Si-Si bond.
Occurence
Silicon is the second most common element in the earth's crust (after oxygen); in fact their compound silica makes up about 60% of the crust.
Analysis of Martian soil[2] shows a composition broadly similar to that of Earth, with oxygen and silicon also taking the first and second respective positions.
Usage
Silicon is the main material for monocrystalline solar cells, used for solar panels. Additionally, it is needed for silicone synthesis to produce synthetic materials.
High-purity silicon (produced by deposition from silanes) is used as a semiconductor in electronics (after being suitably doped). Their are alternatives, such as germanium, though their exact performance characteristics vary and silicon is the obvious choice due to its abundance.
In the form of stones and bricks, silicates are widely used in construction.
Open issues
- How much energy is needed to produce 1 kg of pure silicon for electronics?
References
- ↑ C.E. Housecroft & A.G. Sharpe - Inorganic chemistry 2012. ISBN 978-0-273-74275-3 pp. 433, 444-446.
- ↑ NASA JPL - Mars Pathfinder: Analysis of Martian Samples by the Alpha Proton X-Ray Spectrometer: Preliminary Results Access 2013-04-28.
