Silicon in the periodic system

The electron configuration of the silicon atom

A single electron pair can be found circulating on the only one s atomic orbit of the outer shell around the silicon atom (shell 3), and two unpaired electrons with the same spin can be found on the three p orbits. In other words, the Si atom would be capable of forming two bonds. However, this is an energetically unfavourable state.

Hybridisation

In a silicon crystal four uniform (the same shape and energy level) molecular orbitals called sp3 are formed as a result of the mixing of three atomic orbits on the p sub-shell and one atomic orbit on the s sub-shell of the outer shell of the silicon atom. The energy level of this orbit is higher than that of the s atomic orbits but lower than that of the p orbits. An energetically favourable state will be formed. The name of the process is hybridisation (mixing).

As a result of the hybridisation process, silicon in the Si-crystal will have four valences, thus each Si atomic nucleus will form four single covalent bonds with four other neighbouring Si nuclear cores in a tetrahedral arrangement. 

Molecular orbitals around the silicon cores are also situated in a tetrahedral arrangement.

Key statements

Silicon crystals have a tetrahedral atomic lattice structure, like diamonds. The crystal is held together by strong covalent bonds.

The 2D model of the silicon crystal in the normal energy level

So that the illustration of the silicon crystal could be accomplished later on as simple as possible, only silicon nuclear cores and the fact that each of those cores are attached to four other silicon nuclear cores by single covalent bonds (which is a atomic conjunction created by a commoned electron pair) are shown in this two dimensional model at the atomic sites of the lattice.

The simplest and most common compound of silica is SiO2.
Some of them: quartz, amethyst, citrine, topaz, onix, agate, jasper, chalcedony, opal