Verified answer

Firstly there is no such thing as a silicon dioxide atom! Only the elements exist as atoms.

Silicon and oxygen combine to form a giant covalent lattice. The basic formula is SiO2

Si has 4 electrons in its outer orbit, each oxygen atom shares two electrons, giving a total of 8 [full orbit] and obeying the bonding rules.

You can find a diagram of one of the SiO2 lattices at http://www.chemguide.co.uk/atoms/structures/giantc...

you'll need to scroll down the page some way to find it