Silicon dioxide (SiO2), commonly known as quartz, is classified as a nonpolar molecule. This characterization stems from its molecular structure and the nature of the bonds between silicon and oxygen atoms.
Firstly, in SiO2, silicon and oxygen are bonded through strong covalent bonds. Silicon (Si) has a lower electronegativity than oxygen (O), which results in polar covalent bonds. However, SiO2 has a tetrahedral structure where each silicon atom is bonded to four oxygen atoms in a three-dimensional arrangement.
Although the individual Si-O bonds are polar due to the difference in electronegativity, the overall symmetry of the SiO2 molecule means that the dipole moments of the polar bonds cancel each other out. This symmetrical arrangement leads to an overall nonpolar character of the molecule.
Additionally, SiO2 is a solid at room temperature and forms a network solid structure, which further contributes to its nonpolar nature. In conclusion, despite the polar nature of the individual bonds, the tetrahedral geometry of silicon dioxide results in a nonpolar molecule.