Question

In silica $ (SiO_{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 $(SiO_{2} )$ does not contain $Si=O$ bonds and form giant molecules
The giant molecule of silicon dioxide or silica $(SiO_{2} )$ 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 $SiO_{2}$ units. $SiO_{2}$ 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