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CO2 is a gas,while silica is a solid.Explain....?

CO2 is a gas,while silica is a solid.Explain....?

Grade:12

3 Answers

Anjali Ahuja
askIITians Faculty 234 Points
9 years ago
Hi student
Gaseous state occurs when there are weaker bonds in between the molecules as compare to the solids where strong bonds are present. Same case is there in case of CO2 and SiO2.
In CO2 central C is attached to two O atom by double bond. And CO2 is a descrete molecule and therefore it exists as gas.
Silicon dioxide also called silica exists as a polymer (SiO2)n where n can be a large number), And O-Si-O-Si-O molecules in a polymer lattice. SiO2 is not a descrete molecule and internoleculre bonfing is present. Consequently SiO2
is solid.
Sunil Kumar FP
askIITians Faculty 183 Points
9 years ago
Co2 is a gas because of its symmetrical shape and it is without polarity whereas SiO2 has different types of bond .it can easily form network bonds and in other words the bonds are polar in nautre and it form a network of molecule .It happens because silicon has low electronegativity than carbon
Prateek Mittal
33 Points
8 years ago
CO2 molecule has 2 double bonds attached to carbon, since double bond is stronger and exist as discrete molecule. 
 
while in SiO2 due to its net like 3D-structure and repeated unit of Si-O-Si linkage, it exists as solid.
 
You could learn it as a rule, as when a compound is needed to be covalent but found to be solid then it is due to its net like 3D structure, which makes it stronger and hence also increases its boiling point and melting point. 
 
the same haapens in the case of carborandum(SiC)
 

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