You are not currently logged in. Please create an account or log in to view the full course.
The Kinetic Theory Model: Solids, Liquids, and Gases – 14.1
Generating Lecture Summary...
Generating Lecture Summary...
Generating Vocabulary List...
Generating Questions...
Generating Questions...
- About
- Transcript
- Cite
About the lecture
In this mini-lecture, we cover Topic 14.1 by using the kinetic theory model to understand the differences between solids, liquids, and gases on a microscopic level. In particular, we think about: (i) the size of an atom and what it is composed of (nucleus containing protons and neutrons with electrons surrounding it); (ii) the Particle Picture of the atom; (iii) atoms forming molecules like H20; (iv) the three most common states of matter – solid, liquid, and gas – and their key properties; (v) three examples that show why the difference between a solid, liquid, and gas is not always clear (pitch drop experiment, supercritical fluids, and non-Newtonian fluids), which serves as non-examinable enrichment material to conclude this video.
About the lecturer
Chris Bell is a Senior Lecturer in the School of Physics at the University of Bristol. His research focuses on the creation and control of novel electronic phases of matter in metals, semiconductors, and insulators. Recently his work has centred on low dimensional systems, including low-density high-mobility two-dimensional superconductors as well as ultrathin ferromagnets.
Hi,
00:00:05My name's Chris Bell and I'm a lecturer and researcher
00:00:06at the School of Physics and the University of Bristol.
00:00:09And in this video, I'm going to be telling you about solids, liquids and gases.
00:00:12So we're going to use a simple theory called the kinetic Theory to explain
00:00:17the different states of matter in terms
00:00:21of particles moving around in those systems.
00:00:23So let's start off with reminding ourselves that
00:00:27ever thinking the world is composed of atoms.
00:00:31So the stuff around us,
00:00:34all of these different materials you interact with every day they're made of atoms.
00:00:35So now an atom is composed of a nucleus.
00:00:40So at the centre of the nucleus,
00:00:42protons and neutrons and they're about affect a metre in diameter.
00:00:45So this is a tiny quantity.
00:00:49The atom itself is composed of this nucleus and surrounding it, uh,
00:00:51is a cloud of electrons.
00:00:57And the total diameter of this cloud of electrons is about an and strong.
00:00:59So for something like a helium atom, for example, shown here
00:01:03and so an angstrom is 10 to the minus 10 metres. So this is
00:01:07100,000 times bigger than the nucleus.
00:01:12But keep in mind this number an angstrom, which is 10 to the minus 10 metres.
00:01:14So 1 10 billionth of a metre is the diameter of these atoms.
00:01:20So now, in this particle picture that we're going to talk about today we think of
00:01:26these atoms as actually basically hard spheres.
00:01:32So a little bit like snooker balls or something like that.
00:01:37So we're going to think about containers filled with these balls and they're
00:01:40going to be bouncing around and moving and interacting with each other.
00:01:44And we're going to try to explain the different
00:01:48states of matter in terms of these hard spheres.
00:01:50So it's important to remember that materials are just made up of individual atoms.
00:01:54So something like the gas are gone or the gas helium that I just mentioned.
00:01:59Those are really just single atoms.
00:02:04But there are lots of other materials that are composed of multiple
00:02:07atoms,
00:02:11things like water.
00:02:11For example, water is two hydrogen atoms bonded together with an oxygen atom,
00:02:13and that forms a molecule.
00:02:19So there are, of course, many,
00:02:21many millions and millions and millions of types of molecule.
00:02:23But for all of these different types of molecules and atoms,
00:02:27we're just going to consider them as these hard spheres as a first approximation.
00:02:31Okay, so in this video,
00:02:38we're going to talk about the three most common states of matter.
00:02:39And these are things that you will find day to day. So what are they?
00:02:43Of course, we've got solids,
00:02:46we've got liquids and we've got gases and we're
00:02:48going to go through each one of these in turn
00:02:51and discuss how we can think about these different
00:02:54states of matter in terms of these hard spheres,
00:02:57these atoms or molecules.
00:03:00So remember, there are other examples of states of matter.
00:03:03So the plasma is very common
00:03:06in lighting, for example, you find them in first and tubes.
00:03:08There are the more exotic types of matter that you don't find
00:03:13day to day things like super fluids that happened at very low temperatures
00:03:15and also at even lower temperatures. Bose Einstein condensates.
00:03:19Extremely interesting, but we're not going to talk about those today.
00:03:22Okay, so let's start off with our first state of matter, the gas.
00:03:27So I've got my container here,
00:03:32and I'm going to think about the atoms of the gas moving around in the container,
00:03:35bouncing off one another and bouncing off the sides of the container.
00:03:40So one of the key properties of a gas
00:03:44so a gas expands to fill the container that it has no fixed volume.
00:03:47If I put it in a small container, it will fill that container a much bigger one.
00:03:52It will still fill that container.
00:03:56The atoms, as is shown in the image relatively far apart,
00:03:59and they don't really attract one another.
00:04:04They're weakly interacting.
00:04:07If they happen to hit each other,
00:04:08they will bounce off and they bounce off the sides of the war
00:04:10because they're so far apart. That means the gas is relatively easy to compress.
00:04:13And you know this. We'll talk about this in one of the later videos.
00:04:19You can compress air and you can pump it into the tyres of your bicycle of a car.
00:04:22And so because the atoms,
00:04:27because the molecules or these hard particles that
00:04:29we're talking about are so far apart,
00:04:32we can squeeze them closer together if necessary.
00:04:34So just to give you a feel for the kind of numbers these
00:04:39atoms, these particles are moving around inside this box.
00:04:41So typical speeds at room temperature in air for example,
00:04:45these particles are moving at hundreds of metres per second.
00:04:49So I've already spoken about some of the examples. What do we know? Types of gas.
00:04:53Well, air is mostly composed of oxygen and nitrogen.
00:04:58We've got steam when we boil a kettle of water.
00:05:02So that's liquid water converted into steam. So
00:05:05water as a gas.
00:05:08And then you may have come across helium in balloons or gas
00:05:10that you cook with at home or heats your your house.
00:05:14So these are all common examples of gases.
00:05:18So let's turn to the next state of matter the liquid.
00:05:23What distinguishes a liquid from a gas? So here's our container again.
00:05:27Here's our box,
00:05:32and you can see we've got these particles inside the box.
00:05:33They're not distributed throughout the box.
00:05:37They're sitting at the bottom of the box
00:05:40there, filling the container.
00:05:42They are adapting to the shape of the container,
00:05:45but they're not filling the entire volume,
00:05:48so the volume of the liquid is fixed, but the surface area of the liquid isn't fixed.
00:05:50If I put it in the shallow container,
00:05:56it would spread to fill the shallow container at the bottom.
00:05:58If I put it in a tall, narrow container. It would fill that up.
00:06:01So this is different from the gas,
00:06:06and we can see that the uM particles are much closer together
00:06:08and they're quite strongly interacting, and they're pulling each other together
00:06:13and holding that fixed volume.
00:06:19Because of that,
00:06:24you might guess that it's relatively hard to compress a liquid,
00:06:25and that's absolutely correct.
00:06:28But from this cartoon,
00:06:31we can also say that the particles are moving around continuously.
00:06:34You know that
00:06:38liquids can flow, but even if the liquid is stationary,
00:06:39actually the particles inside are moving around continuously.
00:06:43They are not fixed in a position over time.
00:06:46So you're familiar with liquids. What's a common example of liquid
00:06:51is water.
00:06:56We've already spoken about water.
00:06:57Okay, so the next one that we want to contrast with the liquid is the solid.
00:07:01So what's the difference between a solid and a liquid?
00:07:06While the main thing you know is that a solid will resist that tendency to flow.
00:07:09So when I put my material in this box now, it just sits there.
00:07:16The particles sit there, they don't flow.
00:07:21The volume is fixed, but also the surface area is fixed.
00:07:24It does not adapt to the shape of the container.
00:07:27So in the cartoon here,
00:07:32in this diagram I've got the atoms are closely packed together.
00:07:33They're much more strongly interacting than in the liquid.
00:07:38And they're also in this very regular pattern
00:07:41and again just like a liquid. Because the atoms are so close together,
00:07:45it's hard to compress a solid
00:07:49so very different from the gas that we mentioned before.
00:07:52Now it may look like in this picture that the atoms aren't moving at all.
00:07:56Actually, that's not true. Um, atoms are vibrating.
00:08:00They're held in a fixed position,
00:08:04but they're moving a little bit around a fixed
00:08:06point and we'll come back to that shortly.
00:08:09So what are examples of solids?
00:08:13While there are a huge number of solids, we've got metals.
00:08:15We've got word plastic, ceramics, all kinds of different things.
00:08:18You eat salt, for example, that forms tiny little crystals.
00:08:23There are precious stones like diamonds and sapphire.
00:08:29And these examples salt and diamond are quite interesting
00:08:32because they have this very perfect crystalline form.
00:08:35And this is kind of similar to the cartoon I'm showing here
00:08:40where all the atoms are arranged in a very perfect regular away,
00:08:44and this is called a lattice
00:08:48and these
00:08:51solids and owners crystalline solids. So that's a special type of solid.
00:08:52Okay, so that's the end of the basic concepts distinguishing gases,
00:08:58liquids and solids.
00:09:03But I just want to spend a few
00:09:05moments talking about some slightly advanced questions.
00:09:06So here's a Here's an interesting question is,
00:09:09Are these distinctions that I've just made between solids,
00:09:12liquids and gas always so clear,
00:09:15and I'm going to go through just three examples
00:09:18that explain that it's not always that simple.
00:09:21So if you're interested in some of these, you can do a bit of research on the Internet.
00:09:25So the first one I would encourage you to
00:09:30search for is called the pitch drop Experiment.
00:09:32So Pitch, also known as Bitterman, is an extremely thick liquid.
00:09:35So what do I mean by thick or its high, viscous liquid?
00:09:41It means when you try to pour it,
00:09:45it pours extremely slowly.
00:09:47So I think about if I can add a container of water,
00:09:49I could just pour it out and the liquid flows out very quickly.
00:09:52If I had honey,
00:09:56it takes a little bit longer to pour. So imagine making
00:09:58this material more and more viscous, so it moves much more slowly,
00:10:02slower and slower.
00:10:07Now it turns out that pitch will flow over the course of not days or weeks or months,
00:10:08but years.
00:10:16So there are people who have done experiments where they try to pour this material,
00:10:17and it does pour. But it pours over many, many years, even decades,
00:10:22so that just shows that we have to be a little bit careful that what we
00:10:27think might be a solid may not be a solid If we wait for long enough,
00:10:31we're thinking, and our human time scales, so pitch is very interesting.
00:10:35You can hit it with a hammer, and it smashes.
00:10:39You might think it's a solid, but over time this
00:10:41thing that looks like a solid will actually
00:10:45flow because it's actually really a liquid.
00:10:48It's just the time scale is different to what we're used to as humans.
00:10:50So here's a second example. So in my box now I've got these particles,
00:10:55and you can see that I filled the box very tightly. So there are many, many particles.
00:11:00So now here's the question. Is that a gas Or is that a liquid?
00:11:06And if you look back through the other slides, you may not be sure,
00:11:11actually which one it is.
00:11:15And this is absolutely valid point if you take a gas and you make it very,
00:11:16very hot and very, very high pressure will talk about what pressure means.
00:11:22Actually, the distinction between a liquid
00:11:28and a gas disappears,
00:11:30and this is something called a supercritical fluid,
00:11:33and you can also search for this on the Internet.
00:11:35It may seem a bit exotic, but it actually has practical uses.
00:11:38So you can decaffeinated coffee, for example, with a supercritical fluid.
00:11:41And the very final example I'll give you is something called a non Newtonian fluid,
00:11:46and this is something which has a different viscosity.
00:11:52So we've already talked about viscosity, how it flows,
00:11:56depending on how quickly you tried to apply a force to it.
00:11:59So if I push it
00:12:03so you may have seen this corn flour and water, for example,
00:12:05so if you push corn flour and water,
00:12:09it doesn't like to flow if you push it quickly.
00:12:11But if you push it slowly, it will flow.
00:12:14Ketchup is the opposite.
00:12:17It doesn't really flow,
00:12:19and then you give it a whack, and then it does flow. So this is
00:12:20something that can kind of be a solid and a liquid at the same time,
00:12:24depending on how hard you push it.
00:12:28Okay, so that's the end of this video.
00:12:30In the next video,
00:12:32we're going to talk about density and how the density of these
00:12:33different materials changes when you go from the different states of matter.
00:12:36
Cite this Lecture
APA style
Bell, C. (2022, October 31). Topic 14 – Particle Model - The Kinetic Theory Model: Solids, Liquids, and Gases – 14.1 [Video]. MASSOLIT. https://massolit.io/options/topic-14-particle-model?auth=0&lesson=10161&option=1950&type=lesson
MLA style
Bell, C. "Topic 14 – Particle Model – The Kinetic Theory Model: Solids, Liquids, and Gases – 14.1." MASSOLIT, uploaded by MASSOLIT, 31 Oct 2022, https://massolit.io/options/topic-14-particle-model?auth=0&lesson=10161&option=1950&type=lesson