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Video transcript

let's look at two definitions for acids and bases bronsted-lowry and 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 let's really quickly review what a proton refers to so for a neutral hydrogen atom the most common isotope has one proton in the nucleus so here's my nucleus here's my one proton and one electron outside of the nucleus so here's my electron if we take away the electron we're left with just that proton we're left for the nucleus of a hydrogen atom so we could also say this is equal to h plus so when you're talking about a proton donor donor that's something that's donating an H+ and a proton acceptor is accepting that H+ let's go down here to the dot structure for HCl let's focus in on that covalent bond right one of those electrons came from the chlorine so let me go ahead and draw on that electron here so one of the electrons in the bond came from the chlorine and one of the electrons in the bond came from the hydrogen so in magenta right here so that electron that's talking about this electron right here HCl is going to donate a proton to water so let's go ahead and show what happens a lone pair of electrons on the oxygen is going to pick up this proton right here and the electron in magenta is left behind so these two electrons come off onto the chlorine so let's go ahead and draw the products so we would have we had an oxygen bonded to two hydrogen's but the oxygen just picked up a proton so now it's bonded to three which gives the oxygen a plus one formal charge let's show those electrons right so these two electrons in here and red are going to pick up this proton and those two electrons in red are going to form this bond right here so this is h3o plus or hydronium the hydronium ion alright the chlorine right it becomes the chloride anions let's go ahead and draw that in so we had three lone pairs of electrons and we got one more lone pair right so the electron in green is on the chlorine and so is the electron in magenta so the chlorine picked up an egg of charge it becomes an anion so we get the chloride anion here so the HCL donated a proton so it's a proton donor it's a bronsted-lowry acid so let me go ahead and write that here so bronsted-lowry acid and water accepted the proton it accepted an h+ so water is the bronsted-lowry base all right let's think about the possibility of the reverse reaction so if you think about what must happen the chloride anion must function as a base and pick up a proton from the hydronium ion here so if you think about the reverse reaction I'll put a really tiny arrow going back in Reverse because the equilibrium lies far to the right but if you think about in Reverse the chloride anion would function as a base and this is actually the conjugate base to HCl so let me go ahead and write that here so conjugate base to HCl so we have a conjugate acid-base pair here so let me go ahead and write that over here so we have HCl and Cl minus and think about the difference between these two right there's one H+ difference between that conjugate acid-base pair alright so over here water function function as a base once it picks up a proton over here it could function as an acid so this would be this would be the conjugate acids let me go and write that this is the conjugate acid to our base over here to water so we have another conjugate acid-base pair so let me go ahead and write that over here so we have h2o h2o and h3o plus is another conjugate acid-base pair and once again think about the difference between these two right between h2o and h3o plus there's one proton difference one H+ difference and so when you're dealing with the bronsted-lowry definitions for acids and bases think about think about one proton alright let's move on to the Lewis definition so let's get some room down here so the Lewis definition a Lewis acid a Lewis acid is an electron pair acceptor and a good way to remember that is we have an a here for acid and then electron pair scepter so 1/8 right here and a Lewis base is an electron pair donor and a good way to remember this is if you have Lewis Lewis base right so like a lowercase B for base right over here electron pair donor if we take this be here and just flip it right then you would get a D so that's a nice way to remember that a Lewis base is an electron pair donor all right let's look at the dot structure here for boron trifluoride notice that boron does not have an octet all right so if we count the number of electrons here's 2 4 6 electrons around it so it's not an octet this boron right here let me go ahead and draw this in this boron is sp2 hybridized right if it's sp2 hybridized it has an empty p orbital so we have an empty orbital which I'm going to represent like this and that empty orbital is capable of accepting a pair of electrons so boron trifluoride is going to function as a Lewis acid here and water has a lone pair of electrons that it can donate so water is going to function as a Lewis base so a lone pair of electrons on the oxygen alright we're going to donate that that lone pair right into the empty orbital here we're going to form a bond between the oxygen and the boron so let's go ahead and do that so the oxygen was bonded to two hydrogen's already we're going to form a bond between the oxygen and the boron and this oxygen had still has one lone pair of electrons left which is going to give this oxygen here a plus one formal charge and the boron is bonded to three fluorines and I'm just not going to draw on the lone pairs of electrons around fluorine to save some time here this gives the boron a negative 1 formal charge so let's show those electrons so let me go ahead and highlight the this electron pair in red here so this pair of electrons gets donated right to boron to form this bond right here so notice notice there's no H+ changing here and so that's why we that's why the bronsted-lowry definition doesn't apply to this acid-base reaction we have to use the Lewis definition and so the Lewis definition is a little bit more rhod actually and we can go back up here to the previous reaction right and we can we can look at the definition for lewis acid and base for this one so a Lewis Lewis base is an electron pair donor and notice that's what that's what water is doing here as well it's donating a pair of electrons so not only can we say this is a bronsted-lowry base we could also say this is a lewis base and what's accepting that pair of electrons alright well it's the protons let me go ahead and draw this out right so HCl you can think about HCl is being H+ and Cl minus and that lone pair of electrons right this this pair of electrons is being accepted by the proton so you could say that this proton here is a Lewis acid let me go ahead and use a different color for that so we could say that this proton here is a Lewis acid it's accepting a pair of electrons so you could say that HCl is a source of a Lewis acid which is H+ all right so these are very important definitions to understand