sulfate ion structure (20)

how do we know what is the electronic arrangement of this kind of compound? (the compunds with some atoms (e.g. sulfur in sulfate ion) do not fulfill the octet rule) (especially the ones which are stable, the ones which are unstable include radicals, but sulfate does no)

other examples of this kind of compunds include sulfur trioxide, sulfuric acid, sulfur hexafluoride, phosphorus pentachloride etc