Sulfur trioxide, SO₃, has three equivalent S-O bonds around sulfur and no lone pairs on the central atom. What is its molecular geometry?

Core Concept

Three bonding domains and zero lone pairs give the simplest case: the domains spread evenly in one plane at 120 degrees. Resonance averages the three S-O bonds to identical length, preserving perfect symmetry around sulfur. Because no domain hides a corner, molecular geometry and electron-domain geometry coincide exactly here.