why is silicon oxide a solid at room temperature that does not melt until 1973K whereas carbon dioxide?

Question

melts at 217K and is a gas at room temperature

Answer 1

It is because silicon dioxide (SiO2-sand, glass) has a giant molecular structure. The molecules are bonded strongly to each other and hence have very strong intermolecular forces. Another example would be diamond, which is actually carbon but structurally different.

Carbon dioxide has a simple molecular structure, which had weaker Van de Waal's forces.

Answer 2

This is a very interesting question, actually. You might think that CO2 and SiO2 would have similar properties since Carbon and Silicon are so close together on the periodic table. However, the difference is because Silicon Dioxide is really a polymer that has the structure of Si-O-Si-O-Si-O-Si........while CO2 is just a bunch of individual molecules that can therefore easily evaporate at the drop of a hat. I did read about a Chemistry research paper that successfully forced solid CO2 into the polymer mode with heat and pressure. Polymerized CO2 was completely different in properties from ordinary dry ice, but I can't remember the specifics. Very interesting, though.