Question

$C{O_2}$ is a gas, while $Si{O_2}$ is a solid but both are:
(A) Covalent containing $\pi$-bond
(B) Molecules having $p\pi - d\pi$ bonding
(C) Acidic
(D) Discrete molecules

Answer 1

Hint: Carbon dioxide is a colourless gas with a density about 60% higher than that of dry air. Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmosphere as a trace gas.
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula $Si{O_2}$, most commonly found in nature as quartz and in various living organisms.

Complete step by step answer:

To solve this question we need to consider the following characteristics of $C{O_2}$ and $Si{O_2}$.
In $C{O_2}$ (displayed formula: O=C=O), each molecule is attracted to other molecules because of what is called “van der Waals forces” or London forces.
- Van der Waals forces are a very weak form of intermolecular force where temporary and induced dipoles attract one another.
- Van der Waals forces can be broken with little energy, thus carbon dioxide melts at just over -56.6 degrees Celsius.
In $Si{O_2}$, every silicon atom is bonded (covalent) to four oxygen atoms. Every oxygen atom is bonded to two silicon atoms.
This forms a giant, tetrahedral structure much like a diamond. All the atoms are interconnected by covalent bonds, making the lattice incredibly strong.
This is proven by the fact that $Si{O_2}$ has a melting point of 1713 degrees Celsius (Iron melts at 1538 degrees Celsius).
So the answer is option D discrete molecules.

Note: $C{O_2}$ consists of individual molecules with one central carbon atom double bonded to two oxygen atoms. Whereas, Silicon does not form double bonds with oxygen. $C{O_2}$ is gas but $Si{O_2}$ is solid because the $Si{O_2}$ is in giant molecular structure but the $C{O_2}$ is simple molecular structure. Because of this reason $C{O_2}$ is gas but $Si{O_2}$ is solid.