Why does a silicon atom in a silicon lattice have 4 single bonds?

[CraigH]

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!

 

[SteamKing]

Just because a given shell can have a maximum of X electrons in it does not necessarily mean that a particular atom will have that many. Obviously, if you could fill the outer shell of a silicon atom with that many electrons, the charge balance between the electrons and the protons in the nucleus would be wildly out of whack.

Silicon has a valance state of 4 for various reasons, which makes it chemically similar to carbon.

 

[mfb]

The orbitals in the shells have different energy levels and you get subshells. The outermost subshell of silicon just has 4 places left - they are filled in argon, a noble gas.

@SteamKing: valence bonds between two atoms of the same element don't change the charge balance (as they are "shared electrons").

 

[SteamKing]

I realize that, but if you cram 18 electrons into the outer shell of a silicon atom, something's out of whack.