Lewis Acids and Bases

our final understanding of what constitutes an acid, What constitutes a base was covered by louis. Now, according to the Gilbert Lewis definition, a lewis acid is an electron pair except her. Now we're no longer talking about um Donating H plus or accepting H plus. But in fact we're talking about how the use of electrons in the form of lone pairs can be used to abstract or remove acidic hydrogen from one compound to the next. Or how those lone pairs can be used to attach themselves to another compound. Now here, what fits into the idea of a lewis acid? Well, the first category for lewis acids are positively charged hydrogen or metals. So we can have our hydro knee um or a hydrogen ion. This would constitute a lewis acid. It's positive. So it'll be willing to accept negative electrons from a lone pair. We could also have a positive metal. These are also fall into the idea of being lewis acids, they're all positively charged. So they would freely accept negative electrons from lone pairs next. If you're central element within a given compound has less than eight electrons. In this case they're not following the octet rule. So they have room to accept a lone pair from a Lewis base here, Elements with less than eight electrons are typically from groups two and three elements from group to only have two valence electrons. So think of beryllium And let's say it was connected to to Chlorine. Chlorine is in group seven a. So it has seven valence electrons. Remember when you make a covalin bond, you're going to be sharing electrons now although beryllium is a metal because of its position on the periodic table, it does share some characteristics that are common with other non metals. So we'd say here that the brilliant chlorine bond kind of mimics a co valent bond here. Beryllium came with too long on two electrons and it picks up two more by sharing them with chlorine. Right now it only has four electrons around it so it has room to accept another lone pair to get closer to the octet rule of being close to having eight electrons. Remember elements do this in order to get electron configuration as close to a noble gas as possible. So that would be an example of a group to a element doing this now, Group three A. We could have aluminum, aluminum is in the center, it's in group three A. So it has three valence electrons. And let's say it connects to hydrogen, hydrogen is in group one A. So only has one valence electron. So aluminum came with three valence electrons but it picks up three more by sharing them with hydrogen. So it has six around it. So it can still accept a lone pair to get closer to the octet rule of eight electrons. So these are typical examples of lewis acids. Now, another subcategory which we usually don't talk about because this is really an organic chemistry course. But it does fit the profile. So we can say here that sometimes if you have a central element with pi bonds. So a great common example, you could have C. 02. Okay, so here that carbon is making pi bonds which means that it could accept a lone pair from an outside compound and by accepting that lone pair we'd have the movement of one of these pi bonds to the oxygen. Okay, so this is typical of non metal oxides. When I'm talking about a central element with pi bonds. So non metal oxides just means a nonmetal with oxygen. C. 02 is a good example. Um S. O. S. O. To um S. 03. These types of non metals with oxygen's involved um you know, three minus is that's a harder case but that could also fit this characteristic. So these are the three general groupings for lewis acids. Now that you've looked at lewis acids, click onto the next video to look at louis spaces.

So if a lewis acid is an electron pair except er then a lewis base must be an electron pair donor. Now to be able to donate those lone pairs, you must have extra electrons. So we're gonna say what fits into this definition of a louis space? Well compounds with lone pairs on the central element. So here we have examples. We have ammonia, where nitrogen has a lone pair, water, methanol, the alcohol here and then we have this ether, dimethyl ether. So all of them have in common a central element with lone pairs which can freely donate them to a lewis acid. Now, what else would constitute a louis space? Well even easier compounds with a negative charge. So c n minus cyanide ion, hydroxide ion meth oxide ion. And you're a side eye on here. This thing has lone pairs which you don't see which you can donate. So these basically reference basic layouts for louis space. Now here if we're thinking of a lewis base and lewis acid reacting with one another. So let's say we had for our lewis acid. We had aluminum with florins. So remember aluminum is in group three a so it only has three valence electrons. It picks, it gets to share three more from the flooring so it has six. So it hasn't reached its octet number of eight yet here, I'm gonna react it with, let's say we reacted with hydroxide ion, it's negative. So it's a louis space? For sure. It has an abundance of lone pairs on the oxygen. So what happens here is this oxygen can donate a lone pair over to the aluminum. Now with the Bronston Laurie definition, we donate H plus a compound can donate an H plus and be left behind as a conjugate base. But when we're sharing our lone pairs with another compound, we come along with them. So these two would combine together. So we'd have the aluminum Still with its three florins attached and then the oxygen uses its lone pair to make a new bridge. A new bond with the with the aluminum in the center, it still has two of the lone pairs it's not using plus the hydrogen. Now oxygen was negative but now it's sharing its lone pair with the aluminum. So now it's neutral aluminum on the other hand was neutral, but now it has extra electrons. It's gained from sharing the new bond with oxygen. So now it's negative. So it becomes important to remember charge distribution. What happens when I share electrons with a new compound? I become more positive. What happens when I gain new electrons from another compound? I become more negative. So here we have our acid which accepts lone pairs. Our base which donates lone pairs. We added them together. So that's why we call a lewis acid based product. Typically an AD acct because we added them together. So this is these are the fundamental principles behind the Lewis acid based model. Not that we've seen this. Look to see can you answer the question given below attempted on your own, But if you're stuck, don't worry, just come back and see how we approached that same question.

So this question isn't as simple as it looks. But remember I've given us hints and I've talked about it up above to help guide us to the correct answer. So we have to identify who's the Lewis acid and who's the lowest base in this reaction? We have sulfur dioxide reacting with water to produce sulfurous acid. Well, sulfur dioxide fits one of the definitions. We talked up above. It is a non metal oxide. So it's a non metal and sulfur connected to oxygen. And we said that those typically represent lewis acids where the central element is double bonded and this is what sulfur dioxide would look like and have more of a bent structure. But here let's not worry about that. So here it's a non metal oxide. So it's the lewis acid, therefore the electron pair except er oxygen and water. The lone pairs on the central element oxygen can be donated. So this is acting as our Lewis base together. They combine to give us our ad acct sulfurous acid. Later on, when we explore more and more about acids and the different types beyond Bronston Laurie and lewis and Arrhenius. Those are just classifications. Later on, we'll learn about the two major types of acids and we'll learn that one of these types coined oxy acids, they are typically created by combining a non metal oxide, like sulfur dioxide with water and oxy acid itself is just a compound possessing H plus or more than one H plus connected to a poly atomic ion with oxygen's one or more oxygen's because what is this really when you break it down into its component, that's really just a church plus two of them connected to sulfide ion. So we have our H plus ions connected to our sulfide poly atomic ion which contains oxygen's. So guys just realize that when it comes to classifications of acids and bases, there are three major types. We have a radius, we have Bronston Laurie, and we have lewis and as we go by each one, the definition becomes more and more broad in our explanation and understanding of acids and bases and how they react and relate to one another. So continue onward as we explore more and more about calculations dealing with acids and bases.