Question

What does `VSEPR` say in regard to the structure of `CO_2`, and `SiO_2`?

Answer 1

Carbon dioxide is a molecular gas. Silicon dioxide is a non-molecular solid. VSEPR does not predict these phenomena.

Explanation:

Carbon dioxide, `CO_2`, is molecular, and features unsaturated `C=O` bonds. On the other hand silicon does not form unsaturated bonds in that the individual `Si-O` bonds are longer. Silicon dioxide is non-molecular and forms an infinite array akin to the diamond structure.

These facts simply have to be known.