There is an enormous difference between the physical properties of carbon dioxide and silicon dioxide (also known as silicon(IV) oxide or silica). Carbon dioxide is a gas whereas silicon dioxide is a hard high-melting solid.The other dioxides in Group 4 are also solids.here is an enormous difference between the physical properties of carbon dioxide and silicon dioxide (also known as silicon(IV) oxide or silica). Carbon dioxide is a gas whereas silicon dioxide is a hard high-melting solid.