SO2 seems to be a little confusing as there are several different descriptions circulating. Some books claim that it has an expanded octet, although there is no real evidence to support this. It can be simply described without octet expansion in that there are only 8 electrons around the central sulfur atom.
On a simplistic Lewis structure basis this can be achieved with one lone pair, one dative covalent bond and one double bond. According to bond measurements, however, the two S-O bonds are in resonance and have the equivalence of one and a half bonds each (three electrons per bond). Both of the S-O bonds are of equal length and energy as predicted by this model. The bond angle is that expected from three regions of electron density giving a slightly distorted trigonal planar electronic arrangement and an O-S-O bond angle of 119º.
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