SO3 (sulfur trioxide) is a nonpolar molecule. To understand why, let’s look at its molecular structure and the concept of polarity.
SO3 has a trigonal planar shape with sulfur at the center and three oxygen atoms symmetrically arranged around it. The sulfur atom forms double bonds with each oxygen atom, and the molecule is flat, with all three oxygen atoms lying in the same plane.
Polarity in molecules is determined by the distribution of electron density. If a molecule has a symmetrical shape and the electronegativity of the atoms is balanced, the molecule is nonpolar. In the case of SO3, the electronegativity difference between sulfur and oxygen is not enough to create a significant dipole moment. Additionally, the symmetrical arrangement of the oxygen atoms cancels out any dipole moments that might exist, resulting in a nonpolar molecule.
In summary, SO3 is nonpolar because of its symmetrical shape and the balanced distribution of electron density.