How would you describe the strength of the bonds that result from resonance in so3?

The strength of the bonds in SO3 lies in between the strength of a double bond and that of a single bond.

A resonance structure is used to describe a compound whose bonding properties can not be sufficiently explained using a single chemical structure. In such cases, a number of structures are invoked.

The resonance structures of SO3 show that the compound contain bonds that intermediate between single and double bonds. Hence the strength of the bonds in SO3 lies in between the strength of a double bond and that of a single bond.

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All bonds are equivalent in length and strength within the molecule.

Gaseous SO3 is a trigonal planar molecule that exhibit a D3h symmetry group.

Sulfur has sp2 hybridization and it has 6 outer electrons which make the bonds with the oxygen.

Its constituent sulfur atom has an oxidation state of +6 and a formal charge of 0.

The Lewis structure is made up of one S=O double bond and two S–O dative bonds that doesn't not engage the d-orbitals. ( Thus, SO3 molecule has three double bonded oxygen to the central sulfur atom). This explains the strength.

It gaseous form had a zero electrical dipole moment  because of the 120° angle between the S-O bonds.

Explanation: