Lewis Acids and Bases - Video Tutorials & Practice Problems
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concept
Characteristics of Lewis Acids and Bases
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Now, we're going to say that the third acid based definition was introduced in the 19 twenties by Gilbert N, Lewis an American chemist. Now, this one is a little bit different from what we've accustomed to seeing in terms of NIUS in Boston, Laurie. So let's pay close attention when it comes to a Luis acid. A Luis acid, by definition is an electron pair acceptor. We're no longer talking about um releasing H plus ion or accept or donating H plus ions. That's not even part of the description of an acid. Now, here we're talking about an electron pair acceptor. Now, what are the characteristics of a Lois acid? Well, if you're going to accept electrons, electrons are negatively charged, well, you could represent an H plus ion or a positively charged metal. Great examples we have of course, H plus ion and then all of these metals that are positively charged boron is an exception. Boron is a metalloid. So it has characteristics of both metals and nonmetals. So let's just say that it has a plus three charge. Now, what else could fit under this idea of an electron pair acceptor? Well, we could say if you have a compound or molecular structure, if the central element has less than eight valence electrons, it's not fulfilling its octet rule. So that opens it up to the possibility of an ex of accepting an electron pair. Now, what exactly what central elements could exactly fit under this description? Well, we're gonna say elements that are found in groups two a three A and some transition metals. So for example, we have magnesium chloride because magnesium is a group two way, it only has two valence electrons. It connect to the chlorine. Yes, the chlorine are fulfilling their octet rule. But the magnesium itself came in with its two valence electrons. It's sharing two more. So it only has four total valence electrons around it. It's not fulfilling the octet rule of having eight. So there is the possibility of it being able to accept an electron pair to get closer to that magic number of eight valence electrons. The same thing can happen for a group three A element. So here we have aluminum bromide. Same thing. If you were to dry it out, it would have a total of six valence electrons around it. Three that it came in with. And then three more that it's picking up by sharing with the brom means that are surrounding it. So again, now fulfilling the octet rule, opens up the possibility of accepting an electron pair and then transition metals like nickel or zinc cadmium. They because of their de orbitals, they can expand themselves that opens up to the possibilities of having even more electron pairs. So again, a Lewis acid is an electron pair acceptor. So if the acid is an acceptor, what is a Lewis base? Well, a Lewis base would simply be an electron pair donor. All right. So what can fit under this idea of an electron pair donor? Well, we're gonna say the presence of a lone pair on your central element within a structure, that'd be a key giveaway that you have a Lewis base. So here we have this structure here and we can say that the oxygen has long pairs on it, which it could share with another element, thereby dona donating the electron pair and serving as a low base. Same thing with the nitrogen here. That's part of ammonia. It has a long pair that it could technically share. And in fact, this is what happens when h when um ammonia accepts an H plus, it's using its lone pairs to connect with that H plus. And that's how we get NH four positives. But what else could serve as a Lewis base? Well, this is even easier, the presence of a negative negative charge. If you have a negative charge, you have an abundance of electrons. Remember it's best if you're neutral, if I have too many electrons, I'm negatively charged. So I'm gonna seek out a way of sharing some of those electrons with something that's electron deficient, something that needs a lo a lone pair. So all of these, we have hydroxide. Here, we have the aide ion cyanide ion. And then we have HS minus ion, they all can basically share a long pair with some other element. So again, a Lewis acid is an electron pair acceptor. A Lewis base is an electron pair donor.
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concept
The Adduct
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3m
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Now, the AUC represents the product of a Lewis base acid reaction. Here. In this example, we have two reactants combining together to give us one product. We are taking those two reactants and adding them together. That's why we say adduct, we're adding them together. The first structure in blue here, it's called acetone. It is reacting with boron trichloride and together they add to create this abduct. Now remember that we said a Lewis acid is an electron pair acceptor. We said that this can be represented by H plus positive metals or where the central element has less than eight electrons around it. If we look at boron, boron is in group three A, so it has three valence electrons and it picks up three more by forming bonds with these chlorine. But in total, it only has six valence electrons around it, which opens up the possibility of accepting one electron pair in order to fill, fill the octet rule. So here we're gonna say that this represents the Lewis acid. And if that's luis acid, then acetone represents the Lewis base. It is the electron pair donor. And what it's donating is this lone pair Now, this is a bit different from bros laic acid definitions because in bros and Laic acid definitions, the acid donates in H plus, it kind of just gives away the H plus and stays behind here. If you're donating your electron pair, you're coming along for the ride because your electrons are a part of your core as an element. So here this oxygen is going to share this lone pair with the boron to help make this bond. Remember, a bond itself is just two electrons and look at how the whole structure came along with it. So we're adding together the Leis acid and the Lewis base to give us our adopt. Now this is important. All bro and Lori acids and bases are also Lewis acids and bases. And that's because Lewis is the broadest of the three types of acids and bases. It encompasses all types of acids and bases. Brass and Laurie is a little bit more narrow focused and then areus even more. So we're gonna say however many Lewis assets and bases are not classified as acids or bases under Bronson Laurie or Areus models this year is a Lewis acid, but under Bron and Laurie and IOUs, it wouldn't be an acid because of the lack of an H plus ion. So as you can see, Lewis definition really expands as far as it can in terms of collecting as many different compounds under the acid and base banners. All right, So just keep this in mind, Lewis is the most broad followed by Boston Laurie. And then Areus seems to be the most narrow in its descriptions of what classifies an acid, what classifies a base?
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example
Lewis Acids and Bases Example
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2m
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Here, it says to identify each of the following as a Lewis acid or base, Bronson acid or base or both. So for the first one, we have Cobalt two ion here it is a positively charged metal ion. So we could easily accept an electron pair. Therefore, it represents a Lewis acid. Here, it wouldn't represent a Broin Lori acid because of the lack of an H plus group. So here we're going to say that this is a Lewis acid for B we have nitric acid. Now, nitric acid has the presence of an H plus group. So it could serve as a Boston Lori acid now. But could it serve as a Luis acid? Well, it doesn't have the presence of an H plus immediately doesn't have a positive metal. It doesn't have a central element that has less than eight electrons around it. So we wouldn't exactly say that it's a Lewis acid. We're just gonna say here it's a Boston Lori acid. For the next one. This is, if we were to draw it out, it'd be CH three, which is connected to a carbon double binded to an oxygen and then bonded two and H two. So this is our structure. We're gonna say the presence of these lone pairs here could mean that they can serve as electron pair donors. So this could serve as a Lewis base also because of the presence of long pairs, they could accept H plus ions. So that's also a possibility. So it could serve as a brace lai base. So we're gonna say it could serve both types of bases. So it's both. Then finally, we have co 32 minus the presence of a negative charge means that it has extra electrons that it could share. So it could act as an electron pair donor and therefore be a low base. At the same time, it is co 32 minus, it could accept an H plus to become HCO three minus which is bicarbonate. So it could also serve as a bros and lai base. So it could be both types of bases. Now, this is how we describe each of the following compounds on whether they're a Lewis acid or base or Bronston, Laurie acid or base.
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Problem
Problem
Identify the Lewis acid and Lewis base in the following reaction.
CaO (s) + CO2 (g) → CaCO3 (g)
A
CO2 Lewis Base, CaO Lewis Acid
B
CaCO3 Lewis Base, CO2 Lewis Acid
C
CO2 Lewis Base, O2− Lewis Acid
D
O2− Lewis Base, CO2 Lewis Acid
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