 Okay, welcome to the first lecture. No, it's there. I just looked at it. It is. It's there. We'll get it after class, okay? Okay, there's an attendance sheet being passed around now. Make sure you write your name on it, write your name on the attendance sheet. You can get the aprons and all of that stuff, all the stuff you need for lab. At the bookstore, I guess they're hiding it, so you've got to ask somebody. The Science Club wanted me to tell you that you can get gloves, 12 pair of them for $5 in room 124. So, if you guys haven't bought your gloves yet, 12 pairs should last you throughout the semester if you don't rip any or anything like that, okay? There's that if you want to buy it. Like I said with the owl thing, I'm going to postpone the first owl assignment until Monday. I think it was due Friday. I'm going to postpone it until Monday, so I can help everybody who needs to still register for it. I think there's only like two people. Anybody besides those two people? Three people having trouble. Okay, so what I would ask you guys to do is come to me after class and we'll try to take care of it, okay? Okay, so that being said, are there any more questions before we start? Okay, cool. So, of course, like we were talking about last time on the syllabus, this is chemistry 1406, introductory chemistry. My name is Heath, he's correct, you can just call me Heath. I would actually prefer that, but if you guys wouldn't prefer that, then don't call me that. So, just a little bit of background. Me, I started my teaching career at the University of Utah in Salt Lake. I taught biochemistry there for, I think, a year. And then I moved on to Oregon State University where I taught organic chemistry for quite some time. And then I moved to Lynn Benton Community College, so both of those are in Oregon. Where I taught general and introductory chemistry organic chemistry for that matter. And then now I'm here. This is my third semester here at VCE. I've taught both introductory and general chemistry. I mostly teach introductory chemistry. This will be the third time, fourth time I've taught this. That's my credentials. And of course, this is just a brief overview of what the quiz one essentially asks you. Please go again to the Blackboard site. If you're having trouble finding quiz, or if you haven't emailed me quiz one back, please do so before Friday. Because it's due on Friday. You can only drop one quiz. I would hate to the quiz one to be the one that you drop. Okay, so let's talk about chemistry now. So the course overview. First part of the course, we need to talk about matter. What is matter? What are the properties of matter? That type of stuff. And how these atoms and some are arranged in matter. The next part of the course we'll talk about is change in matter. Changing one piece of matter. No, no, no. There's a camera there. To another piece of matter. So, okay, from now on, this is my spot. Okay, nobody sit here. Pardon? Roger. Okay, so then we're going to talk about the changes in matter. So how matter goes from one form to another. Okay? And then we'll talk about energy. Energy of reactions. How much energy is given off when matter changes from one thing to another. How much energy is needed to make matter change from one thing to another. So it's essentially known as thermodynamics, this part. Very interesting part, I think, personally. And then if we get to it, we can talk about quantum. We probably won't in this class, but it is a part of chemistry and if you moved on to chemistry, 1411 and 1412 we would definitely be talking about this stuff. And what this is is just seeing what happens to matter when you shine light on it, shine different wavelengths of light and how the matter behaves. And that gives you insights into its inherent composition to structure and properties. Okay? So let's go on to chapter one. Matter, measurements, and testing. Calculations. So some fundamental definitions that you'll need to know. Chemistry is the study of matter. So matter, what is matter? Matter is everything. Everything is matter. Okay? Anything that has mass and takes up space. So the only thing that isn't matter is nothing. Okay? So chemistry is the study of everything except for nothing. Okay? So except for like a vacuum. And it's inherent properties. It's chemical properties. What it can turn into what it can come from how it behaves. It's physical properties. What does it look like? What's its density? What's its state of matter? That type of stuff. The changes it undergoes the energy associated with those changes. How much energy does it take? How much does it come? So like I said, chemistry is the study of everything. Matter, what is matter? Anything that has mass and takes up space. So composed of atoms, bonded together in specific arrangements compounds. Okay? So the table, that's matter. The air is matter. Water is matter. What is the property? Well a property is the characteristic of a substance. So like a property of my jacket would be that it's brown. Okay? Or that it's got little lip balls on it. Okay? Energy, what is energy? Well it's the capacity to do work or cause change. So how does that relate to chemistry? Well of course when I put gasoline in my car, my car sparks that gasoline with a spark plug and makes a chemical reaction happen and changes that gasoline into carbon dioxide. And water giving a little bit of energy off and that energy actually helps propel the car. An inherent property of matter of chemistry. So what are the divisions of chemistry? So chemistry chemistry is a very big subject. And as you can imagine just like if you said, I don't know I'm a football player. Right? That doesn't fully describe what that player does. Right? He could be a quarterback, he could be a running back, he could be this or that or whatever. So just like in chemistry, if I say I'm a chemist, well although that is true it doesn't really describe exactly what I do. Personally I'm an organic chemist, but there are many other types of chemistry. Okay? And many other types of chemists. So organic chemistry, which like I said is my personal favorite is the study of matter containing carbon. So really that's quite a small subset of all matter, but quite important especially to you guys because humans are organic beings. Okay? Most of you are going to go into the allied health fields so it's good to know a little bit about organic chemistry. And we'll hit on that more towards the end of the course. Inorganic chemistry on the other hand is the study of matter containing non-carbon elements. So anything that doesn't have carbon in it is known as an inorganic substance. As carbon organic, anything that doesn't have political chemistry, well that's an analysis of matter to determine the identity and composition of that matter. So an analytical chemist would be somebody down at the water treatment plant seeing how much, I don't know, heavy metals is going into the water system. And they're just analyzing. They're taking out samples and figuring out concentrations. Okay? So that would be like an analytical chemist. A physical chemist is a chemist who studies the way that the matter behaves at the subatomic level. Okay? So we haven't gotten into atoms yet. We will in a second. Don't sit here. Nobody's sitting here. What you'll find is that atoms actually even though they're the smallest component of matter that still retains the property of that substance, they are actually composed of other things. Okay? Subatomic particles. Particles known as electrons, protons, and neutrons. Okay? And in fact what you'll find is that even those particles are composed of other particles which we won't even touch. Okay? Very, very theoretical stuff. And of course biochemistry is the study of life at the molecular level. So the types of chemistry we'll really be focused most on in this course are inorganic chemistry for the most part. Then organic chemistry for a little bit, biochemistry for a little bit, and a tiny, tiny bit of physical chemistry within the whole of the course. Analytical chemistry, actually, you'll be doing a little bit of this in the lab. So you'll get exposure to all of these types of chemistry. And I really think that it's valuable and I think we'll have a good time with it, actually. Okay. So what can you do with chemistry? Since it's a study of everything, you can imagine that you can do a lot of things with it. And as you can imagine, if you look around in most of your courses there's probably not so many people in your lecture class. That's because in chemistry everybody has to take it who's doing any sort of science, any sort of health, any sort of anything. And in fact you can see health sciences, microbiology, physiology, botany, nutrition are all quite similar but mostly unrelated disciplines. And in fact you can put a number of other disciplines, probably anything that you in particular are going for. I know that I've gotten quite a bit of emails from you guys already and I don't think anybody said they're going into botany. But most people health sciences. But you can imagine some other things that you may or may not be going into that do have to do with chemistry. So chemistry is known as the central science. And hopefully by the end of this class you will fall in line with that sort of thing. Okay. So the funny thing about chemistry actually, I don't know about funny, interesting, is that we'll talk about it for the whole term, we'll talk about it, talk about what it looks like, we'll talk about how it behaves, we'll talk about all of these things. But we'll never actually see atoms, we'll never actually see a reaction on right in front of us, like two things colliding, making something else. We may get some sort of ability to discern that a reaction did happen, like a color change or a flame or something like that. But we're going to have to really come to terms with the fact that we can't really see these things so we're going to have to represent them as pictures and models and things like that. Which aren't actual reactions, of course, like if I fall here, this is a carbon atom, right? This really is not a carbon atom. But this represents a carbon atom. So that's what we're going to do a lot, is that we're going to pretend that what we have in our hand actually does look and behave as if it were at the atomic level or molecular level. So what we'll find is that we're going to be using a variety of representations or models throughout the class that describe what we believe happens on the molecular or atomic level. So let's look at some of these models. Of course, if you look at that you would tell me, oh that's a boiling glass or a beaker of water. But it's not really a boiling beaker of water. It's really just a picture. That's right. It's a model. So that's what you want to give into the habit of thinking. Like this. This is an enzyme. No, it's just a picture. It's just a model of the way that enzyme looks. We can't actually see that enzyme because they're too small. Our eyes can't see them. In fact, light, its wavelength is too long. And that's why even if we got the most powerful light microscope we couldn't see it. Because they're very, very, very, very tiny. And in fact, only recently have people been able to see atoms, if you will, by methods that are kind of a secondary method. They say, well since we're getting these sort of symbols back from like our electron tunneling microscope it must look like this. And then we can get a picture of what an atom looks like. That may not make sense to you right now. I'm sure down the road it will. You'll watch this lecture. I'm sure in like 20. Anyways, so here's some models of water molecules. Here's another model of two enzymes coming together, binding together. This would be like, I don't know, like if you took a headache or something, you took some aspirin. The aspirin molecule would bind to your enzyme and make your headache go away. And here's an organic structure. So this really is not an organic molecule, it's just a kind of representation. So one thing I want to, and look at this, these are just words. This is describing the chemical reaction. H2O liquid goes to H2O gas. So in fact it's not describing the reaction, it's describing the process of evaporation. So the one thing I want you to always remember and I know it seems obvious, but sometimes you'll forget is that these are not actually the actual things. They're just representations of those things. And it's because we can't actually put our hands on them. We can't actually see them. So it's really a lot of, okay, you're just going to have to believe me. We're just going to have to jump into this and say, okay, this is the way things work. And the thing is, I know it's going to take a leap of faith, but I've been studying this for a long time. And I realize that these truths have just keep coming back and back and back. So it must behave this way. Okay, so let's go back to matter. So matter is anything that has mass and takes up space. We've said that plenty of times now. So that means what? Okay, well if it's something, it has to be composed of something, right? Matter, all matter actually is composed of atoms bonded together or it could, I mean they don't have to necessarily be bonded. But it's composed of atoms bonded together in specific arrangements and compounds, okay? So here's some representations of matter. Penny, that's matter, okay? If you can feel it and weigh it, it's matter. Nickel, razor blade, favorite. See this guy right? This guy there, that's matter. That person, that's matter. His hang glider there, that's matter. Those clouds, that's matter. And in fact the air that he's writing on is matter. In fact, if air wasn't matter, this guy would just fall there, okay? In fact what's happening is the wings of that hang glider are actually resting on the air. Just like if you were in a boat, right? You were sailing around resting on the water. That's exactly what's happening here. And in fact that's why we can fly. That's why we have planes that can fly, right? Or that's why birds can fly, okay? I don't think we would love them. Okay, so we talked about a little bit about properties. What is a property? My coat is correct, right? My hair is correct. Well, let's talk a little bit more detail. Physical properties. So there's two types, two classes of properties, if you will. One is physical properties, the other is chemical properties, okay? Let's go over physical properties right now. Physical properties are those properties that are observable when the substance is in isolation. Okay, what does that mean? If I'm not reacting it with something else. Okay, so if I look at this, it's not reacting with anything right now so we can describe its physical properties, okay? It's in isolation. It's not very reactive substance, so it's not like burning up in the air. So some physical properties of this, well, so some examples of physical properties are color, electrical conductivity, state of matter, melting point, boiling point, density, solubility, malleability, how easily can it be deformed? We can describe the malleability of this thing or the ductility of this. How easy do you think it would be to make this thing into a white? That wouldn't be very easy, huh? Or the malleability, how easy would it be to smash it into like a plane? Not very easy. So not very malleable, right? Not very ductile. It's white. It's solid. So the melting point and boiling point would be a little more difficult to figure out. But a solubility, if I had some water I could throw this thing in there and see if it dissolves. If you've got a mixture of two or more different substances, a lot of times you'll be able to separate them by physical properties. So you can imagine if you had a sand metal system, a sand iron system with sand and iron mixed together. It would be annoying, but you could do it. You could pick out every piece of sand and every piece of metal and put them in two separate containers. That would be separation by physical properties. Look at this. Here you can separate it by other physical properties. You don't have magnetic properties here, but that's another physical property obviously. The iron and the sand have different types or different magnetic properties. Therefore the magnet is able to take the iron filings away from the sand. If you can separate things by physical means, those are physical properties. Does that make sense to everybody? You can separate it by physical means. Those are physical properties. It would be like if you had sand and sugar mixture. What you could do potentially is put that mixture, put water into that mixture, stir it up, and then filter out all the sand. Then the stuff that would come through your filter would just be sugar water. Then you could evaporate that water and you would have sand in one thing and sugar in the other thing. That would also be separation by physical properties. Remember we said solubility is a physical property. Solubility means the ability for something to dissolve in something else. Of course that would be referring to the sugar in this instance and intact the sand and not being able to be dissolved in water. That would also be separation by physical properties. Anything you can do to separate these things physically and get those things substance is out. That's separation by physical properties. Physical properties, we talked about state of matter being a physical property. There are actually four states of matter. Three of them we're going to learn of in this class. Those three are solid, liquid, and gas. The lake is liquid. So for ice for water it's got three different states of matter. Just like anything does, we call them all differently for water because we're so used to them in water. Ice is solid water. If we melt that ice it becomes liquid water, which we're familiar with as liquid water. If we heat that stuff up really hot then it becomes steam. All of those things are still watered. I can take that ice, drink it, whatever. I can take the water, drink it. I can take that steam, pull it down, and drink it. It's all the same stuff. It's just a physical change is what's happening. It's not a chemical change. I'm not changing it into another substance. It's the same substance. Let's look in more detail at these three states of matter. As you see, the solid, why is a solid a solid? Why is a liquid a liquid? Why is a gas a gas? What we're doing is we're taking this solid going to a liquid then going to a gas. This would just be like if I had an ice cube, I could put it in a pot on the stove, put it up gradually, gradually, gradually it would turn to water and then it would turn to steam. Then it wouldn't be in the pot anymore. In fact it would be all over the room. How come it does that? At a very low energetic state which is what taking temperature away from something does. If you freeze something you're actually lowering its energy state. What you find is particles become very, very close together. They arrange themselves in such a way as to where it's the most favorable for them to sit. They kind of wedge inside of each other and they put there what you'll find eventually is that molecules have positive portions and negative portions so they kind of align themselves like little magnets with the positive being next to the negative of the next guy. They kind of arrange themselves very orderly and that's what happens in a solid is that particles are close together and organized because they don't have very much energy to break away from each other. When you give them more energy, i.e. increase the temperature so temperature and energy are the same thing. Let's get the one thing straight. You'll forget and be reminded of many, many times in this class that you just got to realize that the more you increase the temperature, you just, all you're doing is feeding those molecules energy or if you decrease the temperature you're taking energy away from those things. So when we give them more energy what happens? Well the molecules no longer become organized so in a solid they still move very slightly so they just vibrate next to each other because they're trying, they really don't like to be next to each other. They'd really rather be rolling around flying away from each other but they don't have very much energy so their like little magnet forces take over so in a solid they're actually just vibrating vibrating so they have very, very little energy. When we heat them up more what happens? They vibrate more, vibrate more, vibrate more until they start rolling over each other. That's a liquid when they start rolling over each other. In fact, if anybody has a water bottle, don't do it with your coffee mug, you can turn it upside down and watch the molecules roll all over each other. Yeah, exactly. That's exactly what they're doing. That's why a liquid flows because these molecules roll and roll all over each other. So we've given those molecules no energy to do that. In fact, if you took that water bottle, threw it in the freezer in a certain angle or whatever, they would freeze, they would stop moving in that particular fashion and they would be very, very organized until you heat them back up. Now, after the liquid, you give these guys more energy, what happens? Instead of start rolling over each other, they try to break away from each other. They fly off. In fact, they get so much energy that they're flying as fast as like speeding bullets. They're just like flying, flying, flying. As you can see, the liquid only takes up this much volume here but when they become gas, they're flying all over the place. They take the volume of the container and in fact, that's the definition of solid, liquid and gas. Let's go over that. A solid is something that has a defined shape and a defined volume. A liquid is something that has a defined volume but a non-defined shape. Does that make sense to everybody? The liquid has no shape. And a gas has no, or it takes the volume of the container and it takes the shape of the container. The liquid actually takes the shape of the container. So they're all right here, guys. So a defined volume, defined shape for solid, defined volume, shape of the container for the liquid and the volume of the container and the volume, or the shape of the container for the gas. So going this way, that would be increasing in energy, right? Going to the right and then going to the left would be decreasing in energy. Or we could say we increase the temperature and decrease the temperature. Same thing. Notice the organization here. See, what you'll find is the little white balls these are hydrogens. This is water molecules. Little white pieces of these water molecules are positively charged, partially. The red portions are negatively charged. You see how they're arranged, I mean, if you squint your eyes and if you once you get the lecture slides you can tell that the positive and negative portions are kind of aligned with each other. Notice this. Notice this is very organized. This is no longer organized anymore. This is the liquid. And now you don't see the positive and negative being so closely aligned with each other. And then of course the gas, they're just gone, right? They're all gone. And in fact, three gas particles is probably a lot. There's probably to be a quarter of one of a z or something like that. So solid melt due to an increase in energy in liquid species. So I don't know how much more we can talk about this, but a physical change occurs when a substance alters its form but doesn't alter its identity. Okay? So it's like when water goes to ice. It's still water. It just looks different. So it didn't change into, I don't know, gasoline or something like that. It didn't form but not identity. That's a physical change. Okay. So I think we've talked about physical properties enough. Let's go on to chemical properties. Chemical properties are properties that are observable when a substance changes or interacts with other substances. So remember we talked about physical properties being where the substance is in isolation. Okay? So now we're interacting other particles with a particular particle of interest and seeing its chemical properties. Okay? So look at this thing here. This is a blow-up picture of a sodium chloride crystal. Is anybody familiar with what sodium chloride is? Anybody know? Yeah, just tell me. If you guys got the answer, got the itch to answer, just tell me because I love when people yell out. Okay? So yeah, it's salt. So it's like table salt. You put it on your, I don't know, mashed potatoes or whatever you put it on. Right? But look at the thing. So it's sodium chloride, right? The chemical structure of salt is this. I think it's sodium. Cl is corn. Okay? So it's a combination of these two atoms. So it's actually called a compound. We'll get into compounds in a second. Compounds are at least two different types of atoms put together. Okay? So this would be a compound. Let's look at the two elements, sodium and chlorine. Okay? Sodium. So remember, we can eat this stuff, we eat it all the time, we love it, it tastes good, whatever. Right? Sodium itself is an element. So let's look at some of its physical properties. Sodium. Sodium is pictured right here. You guys see it? Silver. You guys see that silver? Super duper reactive. Okay? And that's why they have to, in fact it's in this container with all this electrical tape up over it. It's under loyal because if it interacts with oxygen in the air, it explodes. Okay? So if you were to take a piece of sodium and put it on your tongue, you'd probably blow your face off. Okay? Of course. If I take a piece of salt and put it on my tongue, what happens? It tastes good. Right? So you can see that the physical properties are quite different. Right? Let's look at chlorine. Chlorine is in this container here. Physical properties of this are what? It's yellow. It's gaseous. Right? Very super duper poisonous. In fact this is a good agricultural poison. They've used this in military provinces where they wanted to poison a bunch of people when chemical warfare was still okay. If I were to try to, I don't know, be in a room of chlorine, I would keel over. Okay? So both this thing here and this thing, chlorine and sodium, the elements will kill me. Okay? They could injure me or hurt me back. Right? But, if I look at sodium chloride, right? I eat it all the time. In fact, I probably ate some this morning. You know? Why is that? It's because the compounds, sodium chloride, and the two elements, sodium and chlorine, have different properties. Okay? They have different physical properties. In fact, the chemical properties of sodium and chlorine are such that if you put them together, they will react to form a compound that's completely different than this. Okay? So hopefully everybody sees. Okay? So let's draw chlorine. So this is an element and a molecule. This is a compound and a molecule. But anyway, so this thing has some physical properties. This guy has some physical properties. And this guy has some physical properties. So we're clear with all that, right? When we combine this guy and this guy, the combination shows their chemical properties and what happens is a chemical reaction to form this stuff here. And in fact, to be right, we put two in front of this thing. So we'll get to balancing equations in all that way. So you don't have to worry about that. For those of you who are totally confused as to what's going on. Okay? Okay, so you can see here hydrogen and oxygen, of course, both have different properties than water does. But if we put them together, they form a chemical reaction. So that's their chemical properties combining to form water. Okay? And you can see some chemical properties when I drop different drops of calcium into this solution that looks for calcium. Okay? So they can either get darker or lighter or what? Okay? So chemical properties, again, are those properties that are observable when a substance changes or interacts with other substances. Does that make sense to everyone? Make sense? Most of you are looking at me and they're like, does it make sense or not? Because we could go over this more. I'd love to. This is my job. I'll talk about chemistry all day. Okay, so chemical changes. One chemical change we're familiar with is combustion. Okay? So like this fire reading guy, he puts a bunch of gasoline in his mouth. He lights the gasoline. What does that mean? He's actually using oxygen interacting oxygen with that gasoline and then blowing it out, forming carbon dioxide and water. Okay? That's that chemical reaction that's occurring. Oxidation. The motorcycle here. It used to be iron. Now it's turned to iron oxide because the oxygen in the atmosphere has been interacting with it for so long that it's brusting it. Okay? Iron oxide is rust. Okay? So that's the reaction going from iron plus oxygen to iron oxide. So, what is a chemical change? A chemical change is the process of rearranging, removing, replacing, or adding atoms to produce new substances. So that should have been clear by here. We're just talking about it. Definitely. We're defining it right now. Okay? So substances change in identity, right? They become a different substance. Remember, this will blow my face off. This tastes good. Okay? Keep remembering that stuff. There's another chemical reaction. Magnesium is a silver, well this is a magnesium turning, so it's a silver like kind of strain. Has anybody ever lit magnesium before? Yeah. It's super bright light. Yeah, super, super bright. And that, what you're doing is you're combining oxygen and magnesium. So that's lighting of it. The lighting of it is just giving it enough energy to go. Okay? That's the energy portion that we were talking about before. We're going to get to that way later, but I want you to realize that the lighter is doing nothing except for increasing the temperature. Okay? I mean, getting the oxygen and magnesium to get all riled up to start to increase and end to each other. Okay? And then afterwards, what do we have? We don't have a magnesium turning anymore. We just got dust, right? This magnesium oxide dust. Okay? So that's a comparison, again, of physical and chemical properties. So this is kind of like ashy, and this is really silver. Okay? So I want you to perform this thing, do this problem with me? So classify, if you will, each of the following as either a chemical or physical property. Color, a chemical or physical property? Physical. Physical. Yeah. What about flammability? Chemical. Yeah, that's a weird one, but it's chemical. Yeah. What about hardness? Physical. Okay? You guys getting this stuff? Okay. What about odor? You might think so. It's a weird one. So the odor, it only has to do with the structure. Okay? So the structure of a molecule gives it's odor. So it's in, it's not interacting with anything else. In fact, the so it's kind of convoluted or nuanced, right? So the act of smelling it and realizing what it smells like is a chemical property. Okay? But it really is, it is really physical. Odor and taste, that's why I have these up there. Odor and taste are physical properties, okay? Odor and taste have to do with the structure. Anything that has to do with the structure is a physical property. What about chemical or physical change? Boiling water to become steam. What is that? Physical change. Why? Because steam is the same thing as water, right? It's just in a different physical state. What about butter turning rancid? Chemical. Why do you say that? When you eat butter afterwards, does it taste the same after it's rancid? No. So the structure is changed. Okay? So actually what's happened to that butter is being oxidized, okay? The oxygen in the atmosphere is, that's why you cover your butter up and put it in the refrigerator. Why do you put it in the refrigerator? To keep the energy down, okay? That's what you're doing. What are you doing when you heat up your Salisbury steak banquet dinner in the microwave? Are you doing a chemical or a physical change? Chemical change, right? You're heating those molecules up to cook that beef, right? It's not a, it doesn't, it's not a cow anymore, right? It's a cooked steak, right? Or it's not even a raw steak anymore. You can't, the one thing you want to think about with chemical changes is you can't get them back to the original substance. Okay? So can I get rancid butter back to regular butter? No. Can I get steam back to boiling water? Or water? Yeah. What about burning of wood? Is that a chemical or a physical change? Chemical. Why is that? Because you can't take that ash and make a tree out of it again, can you? Well I can't, you know. Yeah. What about mountain snowpack melting in spring? Physical. Physical change. And decay of leaves in winter. Can I get those leaves back after the decay? No. No way. So what is it? Okay. So before we leave, let's talk about molecules really quick, okay? So molecules appear, appear substance, guys. Let's go have a look at these in a minute. There's a substance that only has one component, okay? So H2 gas, H2O liquid, or AU, that's gold, sorry. Okay? So you can see here this container only contains oxygen, right? So that's a pure substance, okay? This container only contains carbon monoxide. That's a pure substance. This container only contains carbon dioxide. That's a pure substance. If we look at the air right, the air contains what? Carbon dioxide, water, nitrogen, oxygen. Is the air a pure substance? No. What we consider that is a mixture of substances, okay? So there's a difference. Pure substance and mixture. And the last thing we'll go over is what is a molecule? A molecule is the smallest particle of a pure substance. So if we look at this picture here, that's an oxygen molecule. That's an oxygen molecule. That's an oxygen molecule. That's an oxygen molecule. That's an oxygen molecule. So when we talk about pure substance, we're talking about the bulk of the thing. It's a pure substance. When we're talking about molecules, we're talking about the individual particles within that bulk, okay? So thanks for being so attentive, guys. Please do not pack up a minute early. I can't stand that, okay? So from now on, if you guys still need help registering for Al, please come down and talk to me. Lastly, make sure you sign the attendance sheet, because I will only be taking from that attendance sheet if you are here. If you didn't sign it, come down and sign it. Thank you. Bye-bye.