Acid-base definitions

let's talk about the acid-base definitions for bronsted-lowry and also lewis and we'll start with bronsted-lowry so a bronsted-lowry acid is a proton donor and a bronsted-lowry base is a proton acceptor so let's really quickly review what this definition means by proton so if I look at this diagram right here I'm going to draw the hydrogen atom and the most common isotope so hydrogen has one proton in the nucleus and one electron somewhere around our nucleus so negative charge like that and so we would say this is hydrogen alright and then we put it it's one valence electron right there to represent the hydrogen atom or the most common isotope if we were to somehow take away this electron right we would only be left with the proton here we'd only be left in the proton and nucleus and so when we're talking about a proton we're talking about the nucleus of a hydrogen atom which is equal to h plus so no longer are we talking about the electron so let's say let's see how this applies to an acid-base reaction and so we start over here with with water and and then we have HCl over here on the right now in this bond between the h and the CL right one of those electrons came from the hydrogen and one of them came from the chlorine so let me just go ahead and draw those in so the one from the hydrogen I'm gonna put in blue here and that's this hydrogen that's this electron from hydrogen right here in blue and then for chlorine I'm gonna make that electron green so right in here like that and so for this acid-base reaction a lone pair of electrons on the oxygen is going to take this proton right so just the nucleus of the hydrogen atom leaving the electron and blue behind that electron in blue stays behind and ends up on the chlorine and so let's go ahead and draw what we would form from that we would have oxygen here the oxygen had two bonds to hydrogen and the oxygen just picked up another bond to hydrogen and so let me go ahead and and Mark those electrons so these electrons in here in magenta I formed a new bond with that proton so that's this bond right here and then we had some electrons on oxygen let me go ahead and make those in red so these electrons in red right on the oxygen didn't do anything so they're still there so they're right here and that's going to give that oxygen a plus one a formal charge and so this is the hydronium ion h3o plus our other product all right we would also make we would have our chlorine which had three lone pairs of electrons around it already and then it picked up both of those electrons let me go ahead and mark them the one in green that it originally brought to the dot structure and also the one in blue the one it took from hydrogen like that so chlorine now has a negative charge so it's really the chloride anion so this would be CL minus like that and so let's let's identify our bronsted-lowry acid in our bronsted-lowry base for this reaction so let's go back over here and and see what happened all right so the h2o the water right acted as a proton acceptor it accepted a proton from HCl so water would be our bronsted-lowry base an HCl donated a proton to water so HCl would therefore be our bronsted-lowry acid so let's go ahead and identify conjugate acid-base pairs here so if HCl is our bronsted-lowry acid and i can think about its conjugate base over here would be the chloride anion so this would be the conjugate base over here so conjugate base all right so h2o alright was our was our bronsted-lowry base and then over here we can find its conjugate acid it's h3o plus so this would be the conjugate acid over here so when you're looking for a conjugate acid-base pairs you're looking for one proton difference so h2o + h3o plus are a conjugate acid-base pair and HCl and Cl minus are a conjugate acid-base pair and if we look at quickly what we have on the right here alright we are now saying h3o plus as an acid and Cl minus is a base and so one thing you'd think about is h3o plus donating a proton to CL minus and so we'll draw a little tiny arrow going back to the left because the equilibrium for this reaction lies far to the right so you're gonna get a lot more a lot more of your products on the right but just thinking about these definitions right h3o plus will be donating a proton and cl- would be accepting a proton the chloride ana would be accepting a proton but again we know HCl is a strong acid so we know the equilibrium lies far to the right so that's that's the idea about bronsted-lowry let's look at another definition which is actually a little bit more more broad so this is a lewis acid and lewis base so a lewis acid is an electron pair acceptor and so an easy way to remember this is acid acceptor and a Lewis base as an electron pair donor and so one way to remember that this Lewis base is an electron pair donor is to you if you think about this B right being lowercase alright and then just flipping it around right you would get a D here so you would get a D so base is a donor so let's look at let's look at this reaction here and we have this the cyclic ether over here on the left and then we have borane over here on the right now notice there's no octet of electrons around boron right Laurens only surrounded by six electrons here and that makes it very reactive boron is sp2 hybridized which means it has an empty p orbital and so let me go ahead represent the empty p orbital like this it's able to accept a pair of electrons and the ether over here is going to donate a pair of electrons and so let's go ahead and show on show what happens right the oxygen here is going to donate a pair of electrons into the empty orbital right and there's going to be a bond that forms between the oxygen and the boron so the the the ether over here is donating a pair of electrons so that must be our lewis base and boring over here is accepting a pair of electrons so that's our lewis acid let's go ahead and draw the product for our Lewis acid-base reaction here so we have our our oxygen is now bonded to the boron the boron is still bonded to three hydrogen's so we draw those in there like that and let's let's follow some of our electrons here before we finish drawing everything in so these electrons in magenta right formed this bond between the oxygen and the boron and we also had some other electrons right on that oxygen let me go ahead and identify those so these electrons right here and red are still on that oxygen so they are right here on that oxygen that oxygen therefore has a plus 1 formal charge so plus one formal charge on oxygen and boron it gets a negative 1 formal charge now like that and so that's a that's one Lewis acid-base reaction here now the Lewis acid-base definition is is once you get more inclusive than bronsted-lowry if we actually go up here to the previous reaction we can actually classify these using the definition for Lewis acid and Lewis base and so let's look again at what's happening here all right so water is donating a pair of electrons all right well according to Lewis base electron pair donor so we could say that water alright we could say this is a Lewis base and HCl right as accepting a pair of electrons right so electron pair acceptor is Lewis acid so we could call this a Lewis acid so notice it doesn't matter what definition you use if you use bronsted-lowry this is your acid if you use Lewis this is your acid or if you use or over here for base right this is your basic or new bronsted-lowry this is also a base according to Lewis and Lewis acid and base also have particular importance in organic chemistry because you can talk about the term a Lewis acid as being as being synonymous with electrophile so you could you could say this is an electrophile and then you could say lewis bases electron pair donor that's a nucleophile and nucleophile electrophile are extremely important concepts to understand when you're talking about organic chemistry