Final answer:
Silicon dioxide (SiO₂) is a covalent network solid with a symmetrical arrangement of Si-O single bonds, which results in it being a nonpolar substance despite having polar bonds within its extensive crystal structure.
Step-by-step explanation:
When evaluating the polarity of a molecule like silicon dioxide (SiO₂), it is important to understand its chemical structure. Silicon dioxide is a covalent network solid where each silicon atom is covalently bonded to four oxygen atoms, forming a continuous three-dimensional silicon-oxygen network. Unlike the discrete molecules of carbon dioxide (CO₂) that have polar double bonds, SiO₂'s extended structure consists of single Si-O bonds which are shared among many atoms, creating an intricate latticework.
Because of its extensive network of covalent bonds and the symmetry of its crystal lattice, silicon dioxide does not have a dipole moment and is considered to be nonpolar. Each SiO₄ tetrahedron in the lattice is symmetrically surrounded by other such tetrahedra, further contributing to the overall nonpolar character of the substance. Thus, a molecule like silicon tetrachloride (SiCl₄) may be a nonpolar molecule, but silicon dioxide, with its distinct crystal structure, also lacks polarity despite being made of polar bonds due to its symmetrical tetrahedral geometry.