1. The problem statement, all variables and given/known data How does sulfur trioxide react with water to form sulfuric acid 2. Relevant equations This is clearly a Lewis acid/base problem. 3. The attempt at a solution Okay, I tried drawing sulfur trioxide out with three double bonds (as it is traditionally drawn). I know the oxygens are nucleophilic and the hydrogens on the water are electrophilic. Nucleophile attacks electrophile but that gives the central sulfur two lone pairs of electrons. This clearly can't be right because I have never seen a sulfuric acid Lewis structure with two lone pairs. I went to Wikipedia and it says the sulfur trioxide molecule has 2 dative bonds and one double bond. This seems to make a little bit more sense. I had the datively bonded oxygens attack the hydrogens. My question is how does the extra oxygen get appended onto the sulfur? I guess the sulfur, being electrophilic, attacks the nucleophilic oxygen too? Also, on a side note, would this reaction be an example of why sulfur isn't hypervalent - i.e. the above reaction wouldn't make sense if sulfur were hypervalent?