This concern touches on whether sulfur is hypervalent (whether it expands its octet when bonding).

The very first picture mirrors both sulfurs through an increased octet.

The problem is that in the top half of the listed below picture, us are an alleged to end up through sulfuric acid, but we actually finish up v sulfuric acid plus 2 lone pairs (if I drew the mechanism correctly). Go I? (I in reality separated the end the top component of the photo into two parts - first, hydrogen attack oxygen; second, oxygen attacking sulfur - for this reason the arrowhead pushing wouldn"t obtain confusing).

The 2nd picture follows updated chemistry fact. Follow to Wikipedia, sulfur trioxide has actually one twin bond and two dative solitary bonds. Sulfuric mountain is additionally a fee separated species with four solitary bonds, not two solitary bonds and also two double bonds. I seem to end up v the ideal product below without any kind of hand-waving.


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acid-base reaction-mechanism
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edited might 8 "17 at 4:40

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I"ve drawn a much more correct system for the reaction the dilute $\ceSO3$ with water in the fluid phase:


$$\ceSO3 (aq) + 3H2O (l) -> SO4^2- (aq) + 2H3O+ (aq)$$

$\ceSO3$ is a strong electrophile, enough to react quickly with water, i m sorry is a relatively weak nucleophile. A water molecule is added to the structure, helped with by the dislocation the a $\ceS=O$ bonding electron pair in $\ceSO3$ come the oxygen atom, forming the intermediate framework shown. Added water molecules then quickly abstract hydrogen atom from the intermediary (actually, the very first abstraction is far less complicated than the second, so it could have been more proper to present each proton abstraction individually in sequence). The last product the the reaction is sulfate anions and also hydronium cations ($\ceH2SO4$ is a strong acid in water, so it doesn"t yes, really exist together a molecule. The second proton isn"t practically as acidic together the first, yet in dilute equipment both space ionized). The formal worldwide reaction is shown below the mechanism. Notice that in ~ every point the formal fee on the main sulfur atom is specifically the same, zero.

Now, with regards to our small discussion around the actual structure of $\ceSO3$. Timeless valence bond theory, intensified with the ide of hypervalency and also VSEPR theory, characteristics the structure shown, through three twin bonds. The Wikipedia post for $\ceSO3$ mentions one more structure, based on modern valence bond concept computational calculations, with one double and two single bonds. This framework is quite interesting as that does no invoke hypervalency. Indeed, hypervalency is assumed to it is in an old concept, and also not really important in more modern theoretical therapies of chemistry bonding.

However, if one opts to screen the framework according to contemporary valence theory, they would do well to make it explicit. Virtually all structure formulae this day are attracted in the paper definition of timeless valence bond theory. Certain assumptions from the classical theory carry out not bring over to the contemporary theory. Because that example, the authors of the short article "Modern valence link theory", Chem. Soc. Rev., 1997,26, 87-100 (free access mirror) uncover that the bonding in $\ceN2O$, explained classically together a mixture the the canonical develops $\ce^-N= N^+=O$ and also $\ceN≡N^+-O^-$, is finest described as $\ceN≡N=O$. Also with 5 bonds, the central nitrogen atom has actually a calculated occupancy close to 7, i.e. It is no hypervalent. Because the structural building and construction rules of classic and modern-day valence bond theory aren"t the same, the structures produced from both carry out not mesh and also cannot be contrasted directly. The simplest thing to do, then, is to attract $\ceSO3$ follow to timeless valence link theory, through three dual bonds.