Question

Statement:$C{O_2}$ is a gas, while $Si{O_2}$ is a solid at room temperature. State a reason for it.

Answer 1

Hint: Both carbon and silicon belong to the same group, group $14$. $C{O_2}$ and $Si{O_2}$ are oxides of group $14$ elements. But they differ in their physical state. Carbon dioxide contains double bonds between carbon and oxygen atoms. It is found in the atmosphere. Silicon dioxide is found in nature as quartz.

Complete step by step answer:
Carbon dioxide has a $O = C = O$ structure. The molecule contains double bonds. Each molecule of carbon dioxide is attracted to each other by van-der Waals force. It is a weak force of attraction. Van-der Waals attraction can be broken easily. So the force of attraction between the molecules is weak. The bonds between carbon and oxygen are strong and between the molecules are weak. Hence carbon dioxide exists as gas.
Silicon dioxide contains two oxygen atoms per molecule but it exists as a crystalline polymer. It is a giant molecule with tetrahedral coordination. One silicon atom is attached to four oxygen atoms. Every oxygen is bonded to two silicon atoms. All the atoms are connected via covalent bonds. It has a strong lattice. There is a large network of atoms in silicon dioxide. So the force of attraction between the molecules is strong. Hence silicon dioxide exists in solid state.

Note:
Carbon dioxide is a simple molecular structure while silicon dioxide is a giant molecular structure. Hence carbon dioxide is a gas and silicon dioxide is a solid.Carbon dioxide has a melting point $ - {56.6^0}C$. Melting point of silicon dioxide is ${1538^0}C$.