Covalent structures and bonding
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Please explain why carbon dioxide is a gas at room temperature whereas silicon dioxide is a solid with a melting point 1710 celius.
Corrie writes ....
Carbon dioxide has a simple molecular structure, so its physical properties, like boiling and melting point, are determined by the forces of attraction between the CO2 molecules - the intermolecular forces.
As the CO2 molecule, on account of its linear shape, is non-polar, the intermolecular forces will be of the relatively weak van der Waals' type. So carbon dioxide is a gas at room temperature.
Silicon dioxide, on the other hand, is a covalent giant molecular substance, with a structure similar to that of diamond. So all the Si and O atoms are joined together in a giant 3D network. To melt SiO2 a great many strong covalent bonds must be broken. This requires a lot of energy - hence the very high melting point.
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updated: 17 April 2007
