Question

In silica $(Si{O}_2)$ , each silicon atom is bonded to

• A. two oxygen atoms
• B. four oxygen atoms
• C. one silicon and two oxygen atoms
• D. one silicon and four oxygen atoms

Answer 1

Answer: (B)

Silica $(Si{O}_2)$ does not contain $Si=O$ bonds and form giant molecules
The giant molecule of silicon dioxide or silica $(Si{O}_2)$ consists of continuous lattice of silicon and oxygen connected by covalent bonds. In silica each silicon atom is tetrahedrally
surrounded by four oxygen atoms. Thus, there are no discrete $Si{O}_2$ units. $Si{O}_2$ is a network solid.
In silica, silicon has large size, so the $3p$-orbitals of $Si$ do not overlap effectively with $2p$- orbitals of oxygen. Therefore, $Si=O$ are not formed. The tetravalency of Si is satisfied by the formation of $Si—O$ bonds, thus it is surrounded by four oxygen atoms