One Lewis dot structure for a sulfate ion is an S connected by two pairs of dots to two O's, each of which is surrounded by two pairs of dots. The S is connected by one pair of dots to two additional O's.
Each of the O's connecting to the S by one pair of dots has three pairs of dots around it and a minus sign next to it. The Lewis structure should have 32 dots to represent the 32 valence electrons. The structure must have a charge of minus two. The sulfate ion has six possible resonance structures.