Why CO2 is gas at room temperature but SiO2 is solid?

Answer 1

Carbon is a non-metal with a fairly small atomic radius close to that of oxygen. Carbon dioxide consists of molecules in which a single carbon atom is double-bonded to two oxygen atoms. As CO2 is a relatively small, nonpolar molecule it is a gas.

Silicon itself is a metalloid with a relatively large atomic radius while oxygen has a much smaller atomic radius. Due to this difference in size silicon does not easily form double bonds with oxygen. Instead of forming a molecular gas, SiO2 forms a covalent network. In this network each silicon atom is single bonded to four oxygen atoms and each oxygen atom is single bonded to two silicon atoms.

Answer 2

Carbon is a nonmetal with a fairly small atomic radius close to that of oxygen. Carbon dioxide consists of linear molecules in which a single carbon atom is covalently double-bonded to two oxygen atoms. As CO2 is a relatively small, non-polar molecule it is a gas.

Silicon itself is a metalloid with a relatively large atomic radius while oxygen has a much smaller atomic radius. Due to this difference in size silicon does not easily form double bonds with oxygen.

Instead of forming a molecular gas, SiO2 forms a more ionic network (crystalline: quarts. In this network each silicon atom is single bonded to four oxygen atoms and each oxygen atom is single bonded to two silicon atoms.

Added: It also is less electronegative (1.75, comparable with Cu and Sn) than carbon, so the difference with oxygen (3.5) is bigger, thus bonds are more of ionic character.

(The lower you 'go' in the Periodic Table, elements become less nonmetallic, so the more metallic / ionic character you'll find: in group IV: C>Si>Ge>Sn>Pb)

Answer 3

See similar question/answer. No two compounds have identical melting points. Therefore there must always be a temperature at which one is solid and one is not. For these two, there is a moderately wide range of temperatures around room temperature where this happens.

Answer 4

carbon has no vacant d orbital, has small size and there is very effective overlap between 2p orbital of C and 2p orbital of O2. so it exist as gas molecule because of its small size.

whereas Si having vacant d orbital which exist as network as:

Answer 5

CO2 consists of individual molecules with one central carbon atom double bonded to two oxygen atoms.

Silicon does not form double bonds with oxygen easily because of differences in the atomic radii. Because of this SiO2 does not form individual molecules but instead forms a network solid, with each silicon atom single bonded to four oxygen atoms and each oxygen atom single bonded to two silicon atoms. As a result, the particles in SiO2 are not free to move as they are in CO2.

Answer 6

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.