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Silanes
Silanes are binary compounds of silicon and hydrogen with the general formula of SinH2n+2. They have only single Si—Si and Si—H covalent bonds (The simplest one, SiH4 has only four Si—H bonds). Each silicon atom in silanes bonds to four other atoms (either hydrogen or silicon) of which at least one is another silicon atom except in the case of SiH4 in which all four atoms are hydrogen atoms. In this way, silanes are analogues of the alkanes (hydrocarbons with the general formula CnH2n+2) where silanes instead of carbon atoms have silicon atoms. Such analogues aren’t unexpected in chemistry since carbon and silicon belong to a same group (the group 14) and therefore they are expected to have similarities in their compounds. Both alkanes and silanes lack any multiple covalent bonds and are considered as saturated compounds. Both silanes and alkanes also lack any cyclic pattern so they are acyclic. It is possible to have cyclic analogues of them where saturated monocyclic silicon hydrides (saturated monocyclic hydrosilicons) are called cyclosilanes and saturated monocyclic hydrocarbons are called cycloalkanes.
Silicon
atoms are no match to carbon atoms in catenation (bonding together to form lengthy
chains). While there is no limit for the number of carbon atoms in alkanes,
it is hard to synthesize silanes with more than eight silicon atoms due to
stability issues. In other words, in contrast to alkanes, silanes are extremely
reactive and their thermal stability decreases as chain length increases. As
a result, silanes with eight or less silicon atoms are the only well-known
silanes. However, other similar compounds of silicon may have greater
catenation, for example, SinF2n+2
(silicon fluorides) with n up to 14 are known and also in combination
with oxygen, silicon can form unlimited structures like (SiO32-)n
which are polymeric anions in the form
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