 So like I said for those of you guys who just came in, I finished grading the test but not going to hand it back today because I haven't inputted them into the Blackboard but you should be getting your grade today. So you can go ahead and look at it probably by the end of the day. It'll be in Blackboard. So look at it and I'll give you guys the test back on Friday and we'll talk about it. And for those of you guys who are in the online class you'll definitely have your grades by Friday. Okay so the last thing we talked about was polarity of bonds and well specifically of molecules. Let's go over some of these different molecules and see if they're polar or not. So specifically I want to go over a couple of them. We looked at carbon dioxide at the end of last week's or last Monday's lecture. Let's go ahead and look at this again. So carbon dioxide is a linear structure. The electronegativity value of carbon is 2.4 and the electronegativity value of oxygen is 3.1. So remember to determine the bond polarity we're going to look at the change in electronegativity. So we've got, this is always going to be a positive number so we've got 3.1 divided by 2.4 divided by 0.5 divided by that. So what we have to ask ourselves is this a polar bond? Okay so when we get a number here that indicates that this is a polar bond. This was 0 and this would be a non-polar bond. So this bond is polar and remember if we want to write our polarity arrow we write where the positive charge lies at the butt of the arrow put a little cross and then at the head of the arrow we want to put a little arrow there. And that shows where the negative charge is going to. An alternate way of writing this would be delta plus and delta minus. So now when we look at these two atoms here we also have 3.1 over here. So we see we have to ask ourselves well is this bond polar? Right? Definitely is by the same amount 0.7 device. But when we ask ourselves is the whole molecule polar? Well it's not because we've got the same magnitude going this way as we have going the exact opposite way. So they kind of are canceling each other out. So this cancels out with this and the whole molecule is a non-polar molecule. I just did it from my head so I mean did I get them wrong? What are the numbers? 3.5. If I didn't give you the electronegativity table and you had to come up with them in your head then I wouldn't be so concerned about it. But since I'm going to give you electronegativity table write down the right numbers. Because if you don't write down the right numbers it won't make any sense. So let's just do 1.1. So let's look at this next one here or this next molecule here. HF hydrogen is what? 2.1 and fluorine? 4.1. Let's see if the bond is polar. Is that bond polar? Yeah because it's got a number there. If we're going to draw our polarity arrow we're going to draw it like that of course. Can we ask ourselves is the whole molecule polar? Yes it is because there's only one bond and it's polar. So notice the reason this is a non-polar molecule is because these two polarity arrows cancel each other out. One's going exactly this way but 1.1, one's going exactly that way by 1.1. Remember it's a linear molecule that's water. This is also a linear molecule but it's only got the one bond going one way. Let's look at water now. So water, oxygen is 3.5, hydrogen is 2.1, and electronegativity that's going to be 1.4. It's going to be 1.4 going up that bond like that. And this one will also be doing the same thing like that. Having the plus region down here and the minus region up here. Notice again if we add these two arrows up they add up to overall zero because they cancel each other out. When we add these two arrows up kind of like in a vector addition it's always going to be pointing up through like that. So that's going to be the addition of those two arrows so they're not canceling each other out in this case. They're both pointing up, the negative charge region is here, the positive charge region is here. Notice we have to draw this in the proper structural formula. Because if we're drawing it like a Lewis structure say we thought water looked like this we would be incorrect in the analysis of this because we would say that one arrow would be going that way the other arrow would be going that way and they would eventually cancel each other out. So we have to know that this is a bent structure. Because if we thought this was linear we would say this is a non-polar molecule. When in actuality it's a very polar molecule. So again you have to know how to build your Lewis structure. Then you have to do your structural formula just like we've done here and here and then add those vectors up to see if the whole molecule is full. Try it with number three on your own. What you'll find is that's a non-polar molecule, non-polar molecule CH4. And because even though you've got four different bonds that have electronegativity values they all cancel each other. So let's move on to physical state of ionic and covalent compounds. Okay so ionic compounds are usually solids at room temperature. Covalent compounds can be solids, liquids, and gases at room temperature. Of course covalent molecules some covalent molecules that we're familiar with are I don't know like oxygen that's a covalent molecule which is a gas at room temperature. Methane the stuff that comes out of the Bunsen burner that's a gas at room temperature. A liquid covalent compound that we're familiar with at room temperature maybe water. That's a liquid covalent compound at room temperature. And a solid covalent compound at room temperature. Maybe something like wax or like I have a bunch of solid covalent compounds in my skin. You know they're all solids at room temperature. You know most of the structures in my body are solids at room temperature and they're all covalent compounds. Ionic compounds just have very very very strong bonds. These ionic bonds are very very strong. So it keeps the various ions connected to each other. Doesn't allow them to get enough energy to actually break away to form the liquid state or the gaseous state. So ionic compounds are normally, well I can't really think of any ionic compounds that are not solids at room temperature. So that's the difference. Ionic compounds are crystalline. Covalent compounds can be either crystalline or amorphous. Amorphous means that it doesn't have any real regular structure to it. So let's talk about intermolecular forces. We've really been talking about intramolecular forces this whole time. And intramolecular forces are the attractive forces within molecules. Those are better known as bonds to us or shared electron pairs. So chemical bonds are intramolecular forces. These are very very strong forces. They hold these molecules together without allowing them to break apart. But of course there's these intermolecular forces as well. For those of you who've done lab, I think we talked a little bit about it this week in lecture. But these intermolecular forces are the attractive forces between molecules. So when we're looking at the water, said that this is the delta minus region, this is the delta plus region. So when we look at this, what will happen, of course, or what we're discussing here is the difference between something like this, which is a covalent bond, and something like the two molecules. This is the intermolecular. This particular one is known as the hydrogen bond. But what intermolecular forces do, that kind of gives you an indication of what the physical properties of these molecules are. So these bonds here, when these are made or broken, these are made or broken through chemical reactions. When these intermolecular forces are broken, these are broken or made through various changes in physical state. So that's the difference here. So you want to think of this as like physical change in physical state, and this is change. When you break that, you form a different compound, of course. When you break this, you just break them apart, and break these two molecules, not let them stick together. Of course, when you do that, like when you have this regular structure of water here, that would be ice, when they're all really connected in a very crystalline type structure. When you start breaking those intermolecular forces, that's when you've given it enough energy to start rolling on top of each other and become water. So make it go from the solid to the liquid phase. And then when you give it more energy, you totally break down those intermolecular forces to where the different molecules fly off each other and form steam or gaseous water. So again, intermolecular forces are attractive forces within molecules. Intermolecular forces are attractive forces between molecules. And these intermolecular forces determine many of the physical properties. These are the direct consequence of the intermolecular forces in these molecules. Of course, remember, because this bond is polar, right, this bond is polar, overall the molecule is polar. So because the molecule is polar, it likes to attract another molecule. So because of these things that these things are made, okay, because the bonds that the intermolecular forces arise. Okay, so let's talk about solubility. Solubility is just the ability of something to dissolve into something else, okay? So if I say sugar is soluble in water, it means that sugar is able to be dissolved into water. So solubility, the definition is the maximum amount of solute in the case that I gave you, the sugar water example. This would be the solute thing together. So the maximum amount of solute that dissolves in a given amount of solvent at a specific temperature, that's what solubility actually means, okay? So a nice maxim that allows you to remember what dissolves in what is like dissolves like. So polar compounds dissolve other polar compounds, non-polar compounds dissolve non-polar compounds. So that's why sugar is soluble in water. So water is polar, right? So sugar must also be polar, okay? So anything that dissolves in water has to be polar, because water is polar. Polar molecules are more soluble in polar solvents, non-polar molecules are more soluble in non-polar solvents. So we've got to ask ourselves, will ammonia dissolve in water? We could figure that out on our own by taking the electronegativity differences of nitrogen and hydrogen and looking at the particular structure of ammonia. What you would do is figure out, if you did that, figure out that ammonia itself was polar. Water is polar, so would you expect them to dissolve into each other? Yep. So has anybody ever gone down the grocery aisle and gone down the dressing aisle and saw Italian dressing that was kind of separated, right? So what you'll find is, especially with Italian dressing or those types of things, is that when you look at them on the shelf, they kind of have two different layers, if you will, and you've got to shake it up before you put it on your salad or you'll get all the oil out first, right? And it kind of tastes gross, right? But if you shake it all up, it tastes really good, right? It's because of the difference in polarity between water, which is the main component of the stuff on the bottom, and oil, which is the main component of the stuff on the top. Oil is non-polar, which is why it does not dissolve in the water layer. It only sits above it. In fact, oil is less dense than water, too, which is why it's sitting on top of the water layer. So let's go to this slide now. What do you know about oil and water? Well, they don't mix. Why? Because water is polar, of course. Get it into your head that water is polar, because water is one of what's called the universal solvents. So it's going to be the solvent for most of the solutions that you have ever think about in your chemistry career and in your chosen life career. So you want to get it in your head that water is polar. In fact, all the things about water you really want to start kind of memorizing because it will really help you out later. But anyways, since they don't mix, oil must be non-polar. The water molecules exert their attractive forces on other water molecules. So kind of like what they're doing here, right? And when the oil molecule wants to get in between there, the water molecules say no way and squish it out, right? So what it does is it creates this layer of oil right on top of the layer of water. And the oil molecules, they're kind of these long, like, streaming things that like to lay on top of each other. So they like to interact with each other, too. So the oil remains insoluble in water and flows on the surface of water as it was done. If you put non-polar stuff into the oil-water mixture, it would dissolve into the oil part and not the water part, of course. Okay, so let's go back to that interaction of ammonia and water question. You see, just like we've drawn up here about just looking at just a solution of water, right, up here. You can see the same kind of thing happens when you dissolve ammonia into water. Okay, ammonia, of course, looks like this. Everybody probably knows by now. If you're dealt a positive region, if you were to do your electronegativity values, you would figure this out. Here, this is your delta positive region. This is your delta negative region, just like with water here. Okay, so when you get this thing interacting with this thing, you get the same sort of little dashed intermolecular attractions. Those attractions are actually known as hydrogen bonds. Okay, but that's how ammonia dissolves into water. It kind of is attracted to the water molecules and kind of fits in to the water matrix. So if we had an ammonia molecule, it could kind of squeeze into full space that one of the water molecules previously occupied. Solutions of ionic compounds. Let's talk about ionic compounds now. This is all covalent compounds. Compounds, of course, are made up of ions as opposed to molecules, which covalent compounds are made up of. So let's look at a particular ionic compound that most of you should have known for the test. Although I was quite surprised that some of you didn't. Sodium chloride, NACL. When we put this sodium chloride into water, so we can think of it adding it to water like that. What we're really saying is we're going to dissolve this into water. So you can imagine, we've got water. We've got a little salt shaker. We make this salt water. What happens is that this sodium and this chlorine, they don't stay stuck together. They form their ions in CO minus, not associated with any particular place. They're not closely stuck together like they were in solid form. They're just free-floating. When some breaks down in water to its ions and the ions become free-floating, we call these electrolytes, these ions, this free-flowing solution. It's an electrolyte solution. We call it electrolytes because now the solution is able to conduct electricity. Because these ions actually have charges and they allow the electrons to jump from ion to ion to ion. Of course, electricity is just a bunch of electrons flowing through water. So this process of going from the solid compound to its ions here in solution, this process is known as dissociation. So when the ions dissociate, we call them electrolytes. Covalent compounds do the fact that they're not made up of ions. So the difference, remember, is the difference between ionic and covalent compounds. But imagine it's dissolving into ammonia. What would happen is this ammonia molecule would come and grab this ion and take it away. Then it would grab the next ion and take it away. A different one. Grab the next one, take it away, take it away. And then break those up into the particular ions. Of course, covalent compounds like formaldehyde here don't look anything like, or behave anything like, ionic compounds. So they don't dissociate into ions. So when covalent solids dissolve into solutes like water and sugar, so covalent sugars are covalent molecules, they don't conduct electricity, and we call these solutions non-hydrolytic solutions. So let's talk about boiling point and melting point now, specifically covalent compounds. The strength of the attractive force holding the substance together, so remember this attractive force here, holding these two guys together, determines how high the boiling point and melting point is. That plus the size of the molecules. So polarity and molecular weight both determine what the boiling point or melting point of a particular compound is. So larger molecules have higher melting points and higher boiling points, on average, than smaller molecules. Just because it's, imagine how easy it is to throw a bowling ball in the air relative to how easy it is to throw a tennis ball in the air. So you can think about that relative to the role molecular mass plays in boiling point and melting point. The other thing is polarity. If these molecules are very polar, like those, remember those magnets that I was talking about, when you keep them over here, they still want to smash into each other. So it's very hard to pull those things apart, remember. And it's the action of pulling these molecules apart that converts them from solid to liquid, or liquid to gas. So if you've got something that's really hard to pull apart, they're going to have a very, very low melting point or boiling point. So remember if they're very hard to pull apart, that means they're very polar molecules. So polar molecules have high melting points and boiling points, even though they might not have a very high molecular weight. So if we were to compare, like water, which has a very, very low molecular weight, 18.01 amu to butane, which has a much higher molecular weight. I can't think of it off my head, but it's around 60 something. So if you just think about those two relative numbers, 20 to 60, and you've just thought about them on molecular weight standards, you would expect that maybe butane would be three times as high a boiling point as water would be, right? Because the molecular weight of butane is three times as high as the molecular weight of water. But of course that's not the case for anyone who's used like a cigarette lighter nose, right? If you push the button, no liquid comes out of the bank, right? It's because butane's a gas at room temperature. Well, why is that a gas? Why is it a gas at room temperature if it's got such a high molecular weight? It's because it's a non-polar molecule, okay? Water is a very, very polar molecule, which gives it such a high boiling point relative to its size, okay? Water's boiling point is 100 degrees, which is very, very, very, very high, 100 degrees Celsius. And the boiling point of butane, something that's about three times as heavy as water, is I think negative 12 degrees Celsius, okay? So there's quite a dramatic difference between, you know, polar and non-polar molecules with respect to their boiling or melting points. Okay, so here's some definitions that we've talked about most of the stuff. But melting point is the temperature on which the solids converted to a liquid. Boiling point is the temperature at which the liquids converted to a gas. Ionic compounds, of course, have much higher melting and boiling points than circular compounds. You can think of ionic compounds being the most polar things that they're off, okay? That's why they've got such high melting points and boiling points, okay? A large amount of energy is required to break this electrostatic interaction. And what you'll find is the melting points of these types of compounds are about 800 to 2000 degrees Celsius, okay? So it's very high relative to, like, something that's just polar, like water. Its melting point, remember, is zero degrees Celsius. So about 1000 degrees less than something that's ionic, okay? So it goes from ionic to polar to non-polar, right? So ionic is very high at the melting point. Polar is semi-high and non-polar is not high at all. So again, like we've just discussed, energy is needed to break these intermolecular forces. Remember, energy and temperature are the same thing. So we've discussed this many times to where if I say I'm just cranking the temperature up, that just means I'm just giving the molecules more energy, okay? So that's what you're actually doing if you raise the temperature of something. So since energy is needed to overcome these intermolecular attractive forces, the greater the intermolecular force, the more energy would be required, right? That makes sense, right? It's like everybody. Higher melting point of a solid, higher boiling point of a liquid, okay? We'll result in this. Okay, and here you can think of the comparison between ionic and covalent compounds. So composed of what they're composed of, what the electrons do, transfer your share of the physical state, do they dissociate in solution, do they have high boiling point of a liquid? Okay, so ionic and covalent bonds only represent two of the forces that occur between atomic-sized particles and hold these particles together to form matter that's familiar to us. There are other forces, of course, and that's what we're going to talk about right now. Metallic bonding, dipolar forces, hydrogen bonding, and dispersion forces. All of these things, these three at the bottom, are essentially almost the same thing, okay? They're just different strengths of intermolecular forces. So they're all these intermolecular forces here. You're ranking them relative to not very strong, medium strong, very strong, with hydrogen bonding being the most strong out of those two. So, yeah, we know ionic compounds are held together by ionic bonds. They're held together by this. They mean not held together like how this is going to help together. But if you had two molecules trying to interact with each other, that's what they mean by held together. So they're held together by what we call these dye-polar forces. Okay, so why are they called that? Dye, remember, means two, right? Two. So, polar means, you know, this phenomenon of having a plus and a minus charge on you, or a partial plus and a partial minus. So a dye-polar would be something that's like the delta minus interacting with the delta plus or something else, okay? So that's a dye-polar force. Those are what holds these molecules together like kind of not like that. So there are a few different types of dye-polar forces. One of them we've learned about already, this hydrogen bonding. And this occurs, this dye-polar force, hydrogen bonding. Three elements, the most three, electric or negative. And so if you've got water molecules, or you've got an H, O, and then on the next one it's an H, that's a hydrogen bond, okay? If you have ammonia, the same thing, and H. You can see this molecule here, this is ethanol. Everyone's favorite alcohol. You can see the hydrogen bonding, or the intermolecular dye-polar forces here. You see the oxygen atom here has the negative charge. The hydrogen atom that's bonded to an oxygen atom and associated with the other oxygen atom has the delta positive, okay? And that association is called a hydrogen bond. Very, very strong dye-polar interaction. It causes the boiling temperature of water to be so high. That's what causes it. Then we've got these things called network solids that are like diamonds. So if you're, that's a network solid, or this is the structure of the diamond. It's just a bunch of covalent bonds to various of the same atoms. I think this actually is graphite that is showing here. Graphite's almost the same thing as diamond except it's sheets. So the stuff that you write within your pencil is the same thing as diamond. It's just sheets of carbon as opposed to kind of all connected in a 109.5 degree array, you know? So that's the difference between those two structures and what they did quite different results macromolecularly. Pretty interesting. But anyway, silicon dioxide, which is sand, is bonded to the exact same way. So there's a few of these that are kind of these big covalent molecules. So like this is kind of a big covalent molecule. That's what we call a network solid. Nonpolar covalent molecules are held together by these things called dispersion forces. And these are really induced dipoles. I know we're almost out of here. This is a bad one, right? These are induced dipoles, okay? Because of course, nonpolar molecules don't have any polar regions, right? So if you want to think of a nonpolar molecule, it does have, so just pretend this hot dog thing is a nonpolar molecule. It does have electrons, remember, flowing around on the outside of it, okay? These electrons, they don't like to be next to other electrons, okay? But nonpolar molecules like to interact with other nonpolar molecules. So what happens is when two of these nonpolar molecules get kind of close to each other, the electrons from this one feel the electrons from this one, and they kind of get away from it, okay? So these guys get away, say they're concentrated over here at one point in time. So that would mean that this part is more positive, okay? If this part is more positive, this guy makes his electron stick right there, concentrated, okay? This is very, very transient interaction, okay? So that happens just very, very quickly, quickly, very quickly, right? But it does give a weak kind of attraction to these two molecules, okay? So this running around of electrons and making them concentrate somewhere else, is called an induced dipole, because this one induces this one to do, okay? So this is called dispersion forces or induced dipole. Metallophones, these are just kind of like, if you look at your copper pipe, this is just a bunch of copper atoms kind of stuck together, and those atoms are stuck together in kind of just what we call a sea of electrons. So there's all these electrons around them, and they're just kind of floating in the sea of electrons. If you look at this graph, you can see the increasing strength of intermolecular forces. Notice which ones are stronger, which ones are not strong. Notice the dispersion forces at the bottom are only nonpolar molecules. And then there's some selected melting points and boiling points by compound type. This should really emphasize all the stuff we've talked about today. The melting points and boiling points of nonpolar stuff is much lower than polar stuff, which is much lower than ionic stuff. And then there's some more. You can find the sheet that's probably around there somewhere. The test, I'll be putting the grades online today for the new on-campus flag. I'll try to get the tests from the online people graded tonight and put those up tonight too, but probably by tomorrow you'll definitely find out.