Re: Valence
Since silicon atoms generally form four bonds, they are tetrahedral (as is carbon when forming single bonds). The typical shape of a six-membered ring is therefore either 'chair' or 'boat' shaped as in cyclohexane. To form a regular lattice, the configuration that tesselates is the 'chair' shaped one.
Graphene on the other hand, is composed of carbon atoms which are not forming 'single' bonds. Thyey are usually drawn as alternating single and double bonds, although the truth is that they are a hybrid of the two, as this configuration has a lower energy. The bonds in question are in a planar configuration, so graphene itself is truly flat. it is the special properties of the hybridisation of these bonds which leads to the delocalisation of the electrons, and the conductive properties of graphene.
I haven't seriously studied any chemistry for over a decade, but IIRC, the energy level of the bonds in silicon are close enough that they make it a semiconductor, unlike tetrahedral carbon (as in diamond, or in alkanes), which is an insulator.
Biting the hand that feeds IT
