Final answer:
The resonance structures for SO3 include three different arrangements where the sulfur is double-bonded to two oxygens and single-bonded to one, with formal charges applied to indicate electron distribution. These resonance structures lead to a resonance hybrid which describes the true structure of SO3 with equal bond lengths due to electron delocalization.
Step-by-step explanation:
The resonance structures for sulfur trioxide (SO3) represent different ways to arrange the double bonds and lone pairs among the sulfur and oxygen atoms. SO3 has a total of three resonance structures, each featuring a sulfur atom double-bonded to two oxygen atoms and single-bonded to one oxygen atom, with the unshared lone pair of electrons on the oxygen atoms not double-bonded to sulfur. These structures illustrate that the actual distribution of electrons in SO3 is a hybrid of these three possibilities, where the double bond character is actually spread out evenly amongst all the sulfur-oxygen bonds, a concept known as delocalization. This results in bond lengths that are equal, indicating the resonance hybrid nature of the molecule.
In each resonance structure, the sulfur atom carries a formal charge of +2, while the single-bonded oxygen has a formal charge of -1. The other two oxygen atoms are neutral. The molecule itself is neutral, but the formal charges are used to describe the charge distribution in each resonance form. As no one resonance structure accurately represents the true structure of the molecule, the resonance hybrid is the most accurate representation, taking into account the partial bond character between the sulfur and oxygen atoms.