Why is CO2 a gas at room temperature?

Answer 1

CO2 forms individual molecules in which one carbon atom is covalently double bonded to two oxygen atoms. Because these molecules are relatively small and have no dipole moment CO2 is a gas.

Because of its larger atomic radius, silicon cannot form double bonds with oxygen as easily as carbon can.

As a result, in stead of forming molecules SiO2 forms a covalent network in which each silicon atom is single boned to four oxygen atoms and each oxygen atom is bonded to two silicon atoms. Because of this structure the atoms in SiO2 are fairly firmly locked in place.

Answer 2

its molecular bonds aren't strong enough to out weigh their low molecular weight, unlike h2O which has strong bonds and even lower weight but is still able to be liquid

Answer 3

There are weak interactions between the CO2 molecules.