So this is another one of those identified the Lewis acid Lewis base barriers. In this case you see we have two molecules reacting to form one molecule. So in those two molecules we're going to have one that's an electron donor and one that's an electron acceptor. You remember the electron donors are going to be the Lewis bases. The electron acceptors are going to be the Lewis acid. So if you remember, we'll be looking at all of these atoms. You can see that well oxygen and SO3 all the oxygens have their octet filled. If you can't remember to your best for theory. Okay, so that's what sulfur trioxide looks like. NH2O of course looks like that. So this got a full octet, right? They've got a full pseudo octet and all of these oxygen's due to. So this sulfur has already expanded its valence but we know sulfur can expand its valence. So it must be the thing that's accepting the electrons. Since nothing else can accept any more electrons around it. They have the maximum amount of electrons that they can accept. Remember those period three elements in below they can accept higher amounts of electrons to make them more, or what we call expanded valence. So they'll have more substituents around it. So since this thing cannot accept electrons and this thing can, then this thing must be the Lewis acid and this thing must be the Lewis base. Does that make sense? So something that's happening, we want to think about a mechanism of the reaction. Something like this is going on. Okay, and then there's going to be a couple of other subsequent steps. But that would get you to something that looks like that. Okay, so a lot of times it's not so obvious which one it is if it's not, kind of draw the best for structures that you know how to do. So let's just go ahead and label them. Which one was this? Did we say? The acid. The Lewis acid. The Lewis acid is the electron acceptor. Okay. Can you see it accepting the electrons? The Lewis base. The electron donor. Okay. Any questions on that one? You see that?