CO2 consists of individual molecules with one central carbon atom double bonded to two oxygen atoms. Silicon does not form double bonds with oxygen. CO2 is gas but SiO2 is a solid because SiO2 has a giant molecular structure. CO2 has a simple molecular structure, and because of this, CO2 is gas but SiO2 is solid at room temperature.
Because of their structure . Silica has a chain structure with e one silicon atom bonded to 4 oxygen atoms in the lattice. The structure is a long chain of tightly held atoms and this forms a solid.
The carbon dioxide molecule however as a linear structure and each oxygen atom is bonded by double bonds. These double bonds are not as strong as the Si - O bonds in silica so will not form a chain structure.
