 Hello, this is Professor Stephen Nesheba, and I want to tell you a little bit about Lewis-acid-base theory, of which the general idea is that this molecule called an acid combines with the base. It's got a lone paired form. This resulting molecule, which is called an adduct, or a Lewis-acid-base adduct, that's what AB is, and the bond between them is called the dative bond, which is basically a covalent bond that forms when one atom, the Lewis-base, has supplied both of the electrons for the bond. So, going on here then, here we're going to think about carbonic acid forming from the reaction of carbon dioxide in water as a Lewis-acid-base reaction, and what we've got is a four-step method to think about that, and that's what we're going to walk through. The first part is to draw Lewis structures of the reactants, and then so on. So, drawing the Lewis structure of the reactants, here we go, there's carbon dioxide, and there's water, and then the next step will be to identify the Lewis acid in the base, and the Lewis-base, and since I know that there's going to be a bond between that carbon and that oxygen, there's really no real choice here, only the oxygen has a lone pair of electrons to supply to form that bond, so therefore the water is going to be the Lewis-base, CO2 is going to be the Lewis-acid. Next step is let's see how the electrons move to form the acid-base adduct, so I'm going to just lasso those, that pair of electrons, attach it to the carbon, and if we're following the octet rule, that means that a pair of electrons has to leave that bond and be lone pair of electrons on the Lewis-acid, and now the fourth step was let's show the adduct with the data bond highlighted, so here this whole thing is the Lewis-acid-base adduct, and I've shown in blue the data bond, and I've kind of shown that here as well. Now, so I've just labeled here data bond, data bond in both cases. Now, if we're thinking molecular orbital theory instead of valence bond theory, we wouldn't be thinking of a localized bond, but there should be an orbital that has two electrons that is bonding between the carbon and that oxygen, and indeed here's one of those candidate orbitals for that, and so we would maybe call that a data-bonding molecular orbital. Now, in the case of this reaction, there is actually a second step, it's a rearrangement, and it's due to the fact that if you look at the formal charge on that oxygen, it's a minus one, formal charge on that oxygen is a plus one, so what this adduct will actually do is pull those electrons back onto that oxygen at the proton leave and attach it there to make what we recognize as carbonic acid. So here's the summary of that two-step reaction. We have the reactants over here, carbon dioxide in water, undergoing a Lewis-acid-base reaction to form the adduct, which has got this data bond and these excess formal charges, which then it rearranges to form what we recognize as carbonic acid, and here's just a couple of other things to the possible Lewis-acid-base reactions to think about, and here's fluoride with the H3 and so on, and one would go through the same process, four-step process to understand how these reactions go complete as Lewis-acid-base reactions.