Question

why is CO2 a gas at room temperature,while SiO2is a solid??? please answer fast and thank you.

Answer 1

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CO2 exists as a discrete single molecule as O=C=O. and due to only van der waal's interactions the intermolecular forces are not strong enough, allowing the molecules move about freely, hence it exists as a gas.

SiO2 however actuall exists as a polymeric network as O-Si-O-Si......., here each Si atom is bonded to O atom by a single bond and also to 2 other O atoms making it strongly bonded. Due to this the intermolecular forces are tremendously high and molecules cannot move about freely, Hence SiO2 is a solid.

Answer 2

Answer:

It is because of the structure of the CO2. Two of carbon's valence electrons hybridize into two sp hybrid orbitals. As a result, the molecule is one dimensional with an angle of 180∘ between bonds and completely non-polar. The Si, on the other hand, does not form such bonds and the angle is far from 180°, which in conjunction with oxygens high electronegativity makes it quite polar. Thus the interaction between neighboring Si and O atoms of different SiO2 molecules is much higher and as a consequence you need much more energy to break the solid, giving it an increased melting point.