Question

The structures of carbon dioxide and silicon dioxide are shown in the diagram below.

Use your knowledge of structure and bonding to explain the following:

a. Carbon dioxide is a gas at room temperature.

b. Silicon(IV) oxide is a solid with a high melting point.

c. Neither carbon dioxide nor silicon(IV) oxide conducts electricity.

Answer 1

a) Carbon-dioxide is a gas at room temperature because carbon belong to the group 14 and the atomic sizes of both the carbon and oxygen are almost equal. They can easily form double bond. Carbon and oxygen effectively able to form p.pie- p.pie overlapping due to this Co2 doesn't form giant molecules. co2 molecules have linear structure and are non- polar. The intermolecular forces in between the individual atoms of the CO2 molecules are so weak that they cannot form aggregate molecules. That's why carbon dioxide is gas at room temperature.

B) Silicon (IV) oxide is solid with high melting point because silicon also belongs to group 14 but in silicon dioxide silicon and oxygen has high differences in their atomic sizes. Silicon atoms are bigger than oxygen atoms. Therefore there is appreciable difference in the 3p orbital of silicon and 2p orbital of the oxygen due to which it doesn\'t provide effective path for p.pie-p.pie overlapping. SiO2 doesn't form linear structure instead it forms a giant three dimensional structure of [(Sio2)n] in which each silicon atoms is bonded with 4 oxygen atoms tetrahedrally and each oxygen atom bonded with two silicon atoms. Because of this giant structure SiO2 is solid at room temperature and also having high melting point.

c) Carbon dioxide and silicon (IV) dioxide both donot conduct electricity because in order to conduct electricity it requires free or mobile electrons and in both these molecules they don't have free electrons to conduct electricity.

Carbon dioxide and silicon (IV) dioxide both donot conduct electricity because in order to conduct electricity it requires free or mobile electrons and in both these molecules they don't have free electrons to conduct electricity.