Silicon has 14 electrons, this means if it fills up its first two shells it will have 4 electrons in the outermost shell (These are the valence electrons). This shell can have 18 electrons in it, so silicon can have 14 more electrons in its outermost shell. This means it could potentially form 14 single bonds , or 7 double bonds with other silicon atoms. So why does each silicon atom in a silicon lattice have 4 single covalent bonds? I've not studied chemistry since I was 16, so I could be wrong on everything I have said so far. I'm trying to understand doped semiconductors for an electrical engineering class and i thought i'd try and understand the underlying principles before I go into the more complicated stuff. Thanks!