Lewis Dot of Sulfur Trioxide
S does not follow the octet rule. It will hold more than 8 electrons.
Sulfur having valence electrons in the 3rd energy level, would also have access to the 3d sublevel, thus allowing for more than 8 electrons. NOT IN THIS MOLECULE.
Elements in the first 2 periods of the Periodic Table do not have access to the d sublevel and must adhere to the octet (or duet H and He) rule.