#SO_2# is bent when you draw out the lewis dot structure (and a resonance structure):
![upload.wikimedia.org](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e4/Sulfur-dioxide-2D.svg/160px-Sulfur-dioxide-2D.svg.png)
![www.chemistry.mcmaster.ca](http://www.chemistry.mcmaster.ca/~chem1a3/tutorial/so2.gif)
#SO_2# is asymmetrical with respect to the central S atom and so has a dipole. The electrons are not equally shared in the S-O bonds also, because O is more electronegative.