 Hi, I'm Zor. Welcome to InDesert Education. Today I start the new part of the course. It's called atoms. Some of the material in this part you have already started basically in the previous part, which is called electromagnetism. At the same time it's very important actually to understand how internal structure of our matter actually is. And I will put a little bit more details into this part right now, relative to whatever was known before. All right, so this part of the course is presented on Unizor.com. It's part of the course called Physics for Teens. It's a totally free course without any advertisement. There is a prerequisite one, which is called mass for teens on the same website. And I do suggest you to familiarize yourself with all the material in the mass for teens course. Or maybe you already know this, which is great obviously. It's very important actually to study this course from the website because it contains hundreds of lectures. They are all organized into parts, chapters and individual lectures. They are all interrelated obviously. I'm trying to put them in such a logical sequence that there is nothing presented in subsequent lecture, which is not based on the previous ones. So it's supposed to be in logical sequence. Plus every lecture has textual notes on the website. You have the visual presentation and textual at the same time. And it's written basically like a textbook. So you have the advantages of both live presentation and the textbook basically about the same thing. But it's still obviously I'm not reading that textual part. I'm just explaining something. And textual part might be a little bit more detailed in some cases or have some picture better than whatever I can draw on the board. There are problems solved. There are exams, which you can take as many times as you want on the website. So the website is very important actually for the studying of physics in this case. To start this particular part of the course, the atoms, people always wanted to know what's the structure of our matter. And it started long, long time ago before they were familiar with let's say electricity or any other things. So the history of structure of our matter or attempts actually to understand the structure of our matter goes well way back to ancient times. Somewhere around 400 before current era, the time of prospering Greece and philosophers and I shouldn't say scientists, but basically those philosophers were kind of scientists. They were the first ones who attempted, at least to our knowledge, who attempted to understand what's the structure of the matter is. There are some names and I put into textual part of this lecture more names. But one of the person who usually is quoted in this particular regard was the guy called Democritus. I don't know how to pronounce it correctly, probably Democritus, who basically said that matter is supposed to contain certain small parts. And what's important is he coined the name for these parts. He called them indivisible. Now indivisible in Greek is a Thomas. A is negation in divisible, so it's negation of divisibility. And Thomas probably means something like divisible. So these two words came together and our current word atom or atom, atomus comes from those Greek atomus, indivisible. Now their concept of indivisibility, although they call it atoms, if we just take the word as it is, it actually corresponds to our concept of a molecule. Atom is something smaller than that. So let's talk about molecule first. So you take, let's say, a drop of water, you divide it in half, then you divide it in half again and again and again. Is there a limit of this? Well, and the answer is yes. There is a small minimal amount of water, and this is a molecule, which retains properties of water. If we start dividing it even further, I mean, if we can divide it even further, that would be no water anymore. So in some way, the democratist was right calling these parts indivisible, because if we really divide it, we don't have the same matter anymore. So that was about 400 BC. And then for some reason, and I'm not going to go into reasons for this, for about 2,000 years, the progress in this particular area was probably not existent, quite frankly. Only with such people as Galileo and Newton, which is what, 17th century, maybe a little bit before that, only at that time people started progressing in their understanding of what our matter actually is. That was the beginning of experimental physics, because people like Galileo, they made a lot of experiments. With different things, and Newton as well. So at that particular time, Sir Isaac Newton, for example, expressed opinions which are very similar to those of democratists, about something like a small piece of matter which is indivisible anymore in some way, which still retains the properties of the matter. And then after these initial attempts, these initial experiments, the science started really like exploding, because many people were interested in this, and many very smart scientists devoted their time, excuse me, devoted their time to research and experiments and theories. Well, and now I have to really talk about the theory. You see, whatever we are learning, studying in theoretical physics, is basically studying our understanding of what the world actually is. It's our model. That's very important, and the models are changing as the science is progressing. So at the time of democratists or Newton, for example, people understood matter as containing small pieces. Now, what kind of pieces? Well, as many kinds, as many different kinds of matter exist. Water is one thing, gold is another thing, oil is the third thing. Water in the ocean is a completely different thing from the pure water, because there are some salts dissolved there. So people were kind of thinking that every kind of matter has its own smallest pieces, which basically combined together make this matter, which is again our kind of concept of molecule. But then, Dalton, I think it was called Dalton, let me check. Yeah, 19th century, that was 19th century. He suggested that there are certain smaller components than molecules, which combined together make up the molecule. Now, that was a very important scientific achievement, I would say. And let me make an analogy. Let's consider two different languages. The language which is using hieroglyphs or glyphs to name certain concept. So there is a glyph for a chicken, and there is a glyph for water, and there is a glyph for everything else. So every kind of concept, matter, kind of something has its own glyph, and glyphs are very, very complex. Another approach is alphabetical languages. So they have certain number of letters, like 26 in English or 33 in Russian. And combined together in different order, they are making different lengths of words, and the whole word actually is replacing one particular glyph. So what's the difference? Well, the difference is that if you have, let's say, 100,000 glyphs, you might have only like 20, 30 letters. And combined together, these 20, 30 letters make up different words of different lengths, and the total number of words will be, well, exactly the same as total number of glyphs. But it seems simpler to learn. Instead of remembering all these 100,000, we really have to remember the letters and some rules using which we can combine them together to name a particular, you know, concept or whatever. So that was actually something which is an extremely important achievement or simplification of approach, that, yes, we do have hundreds of thousands of molecules, different ones, but there are certain very limited number of elements, atoms of which actually combined together make up all these molecules. Okay, so that was a very important achievement, and now people were basically starting to differentiate the atoms and molecules. And they started researching different elements and how combined together they are making different molecules of different matter. So if you combine, let's say, hydrogen and oxygen, you will have water. Now, another important achievement was that to make water from hydrogen and oxygen, you really have to do it in certain proportions which are exactly the same, no matter how much water you want to make. So it's supposed to be like two molecules of hydrogen and one molecule, two atoms of hydrogen and one atom of water to get the water. So this is hydrogen atom, hydrogen atom, oxygen atom and they are making the water. So basically these types of formulas, if you wish, they became very important for scientists and they were examining the properties of different atoms. So that was a very big step forward. Again, it's attributed mostly to Dalton and his followers. Okay, so hundreds of thousands of molecules can be built using a relatively limited number of elements. And every element is basically an atom from which all these molecules are built. So we are going deeper and deeper from matter as a whole. We have brought it down to the minimum amount of that matter which still retains the properties of matter, that's the molecule. The molecule is, again, we go down into the molecule, into the structure of the molecule and we see that it contains atoms of different elements. So now the multitudes of molecules can be built from a relatively small number of different atoms of different elements. Okay, we are going deeper and deeper. Alright, now that's the time when we have to go even deeper into the atom. One of the first very interesting achievements was when the scientist by the name J.J. Thompson has discovered electrons. So he basically discovered something which was really part of the atom. That was, I think, in the 19th century, end of the 19th century. So that was the beginning of explosion, really, of scientific knowledge at the time. So the discovery of electrons was one of the first ones. Okay, so what's next? Next we had to really build a model of atom. So electrons were negatively charged particles. By that time, by the end of the 19th century, people were dealing with electricity quite comfortably. Maxwell's equations are already on the way. Now, so what is the atom? The atom is supposed to be electrically neutral. Electrons were discovered. So how do they fit into the atom? Now, at that time they came up with a model called Plum Pudding Model. So if you just think about the pudding, it's basically some kind of a mass of the pudding with plums in it. So the idea was that electrons are inserted into a positively charged something, and that what makes actually an atom. Something like a ball of positively something, substance, whatever that substance is, with small negatively embedded into the substance electrons. Well, okay, but at the same time, as I was saying, the experimental physics was extremely well on its way. And experiments with bombarding so-called alpha particles, which are emitted during the radioactive process. I think they were using zinc or gold foil. So they have discovered that all these alpha particles, and they're not talking about what they are, so these alpha particles, some of them just went through and some of them were reflected in different angles, including reflected back into the source of alpha particles. So these alpha particles were produced by some radioactive process. At that time, people really were familiar with radioactivity. They didn't know what it is, but they were familiar with what actually is happening. So it looks like the plum pudding model could not really satisfy this, because if these plum pudding kind atoms are combined together into a matter, into molecules or whatever, then there should be nothing going through. So it was Rutherford, Ernst Rutherford, who suggested the planetary model, planetary model of atom, suggesting that the positive charge is concentrated in a small nucleus, and electrons are rotating around this nucleus. That's what makes actually atom electrically neutral, positive and negative. But since electrons are somewhere on the orbits around the nucleus, then there are basically holes alpha particles can go through in between the nucleus and electrons, wherever electrons are. Now, calculations and experiments, etc., showed that probably atom is practically empty, so nucleus might actually take something like one thousandths of the total size of the atom. That's the difference, one thousandths of the whole size of the atom. Well, the problem is that by that time, the theoretical physics was really on a very, very high level of development. So people knew about the Coulomb's law, about Newton's laws, of course, mechanical laws, and they were saying that, look, I mean, we know that accelerating electrons are basically emitting energies. It's oscillating electromagnetic field. That's what it is. And we know from the previous part of this course that all these effects of induction, etc., it's all more or less was known at the time. So, if electrons are rotating around the nucleus, well, they basically are rotating because there is a centripetal acceleration. Otherwise, they would not be going around the nucleus, they would just fly away. Now, obviously, they were thinking that positive nucleus and negative electrons are holding together that thing. But again, this problem still exists. So whenever electron is circling the nucleus, it's undergoing the accelerated movement with the centripetal acceleration. So it's supposed to lose energy. It's supposed to oscillate electromagnetic field around it. If it loses energy, it's supposed to go closer and closer to nucleus. It's losing its potential energy, obviously. And eventually it will just fall on the nucleus, which means basically collapse of the whole model, which cannot be right, which means the model is wrong. And it usually happens this way. First, people create some kind of a model. Well, the model satisfies certain degree whatever the experiments are. But then new experiments, new facts observed, et cetera, prove that the model is not really sufficiently explaining all these experimental results. Well, that was a real kind of problem because people were really satisfied with the planetary model at the time. Well, at that time, approximately at that time, Einstein came up with his quantizing energy of electromagnetic field. It was actually related to photoelectricity effect. So he wrote about, and we did actually talk about this in the electromagnetic part of this course, he wrote that most likely the energy is consumed or emitted in quanta, which is called photons. Now, if we're talking about electromagnetic oscillations with frequency F, then there's a Planck's constant H, and that's the energy of one particular photon. So that was related to photoelectricity effect. This quantization or quantization of the energy of electromagnetic field. So Niels Bohr suggested another model, which is kind of based on ideas of Rutherford and Einstein. So this is the Bohr's model of the atom. And we did talk about this when we talked about the photoelectricity effect, et cetera. The Bohr's model actually kind of postulates that there are certain shells or orbits, if you wish, where electrons live and they do not emit any energy while they are moving within that particular shell around the nucleus. But there are different shells, and whenever electron jumps from one shell to another, it either consumes or emits the energy, and the energy is quantized in exactly this type of way. So if there is certain movement from energy level 2 to energy level 4, well, that means there is a certain amount of energy emitted, and that's why there is a certain frequency of electromagnetic oscillation produced, or light, if you wish, if we can detect it. And that was the second problem with Rutherford's model. The second problem was that if you observe the light emitted by certain gases, for example, whenever they start glowing, if you have electricity, you have positive and negative, for example, contact in some kind of a tube with a gas. With sufficient amount of electricity, gas starts emitting light. Now, so the energy, the electric energy, it goes into the atoms, it excites electrons of this particular gas, of the atoms of this gas, and whenever they are excited, they are going from one energy level to another. So going up the energy level, they consume electric energy, but then eventually the upper parts of the atom are overloaded and the electrons go down back to their original level and emit light. So the light emitted by specific gas has specific colors in its spectrum. So they took the light, they went through the prism, and they saw specific spectral lights. And every gas has its own spectral lights, and that's quite stable. It's independent of how much energy we put into these electrodes or temperature or something like this. So the spectral lines were characteristic of the gas, which is in that tube and it starts emitting light. So exactly how can it be explained using the planetary model? It cannot, but if you take the idea which is presented by war, that these particular lights are emitted when the electrons are jumping from one level of energy to another, and these levels of energy are specific, which means that the frequencies are specific. So you have certain frequencies emitted by jumping of electrons from one particular energy level to another. So that was very important. So the Bohr's model was actually a progress over the planetary model suggested by Rutherford by basically addressing these two things, that electrons do not actually fall, do not always emit energy and fall on the nucleus. That was one problem with the planetary model and another that the gas, if you put electricity into it, emits always the same spectral lines. Any particular gas has particular spectral lines of the emitted light and it's not dependent on the power of electricity which you put in, etc. Well, I think that at that particular time we have reached a very important stage in the development of our views on atom. So Bohr's atom model was kind of accepted at the time and although since then there are many other developments which are considered to be contemporary physics, that's beyond the scope of this particular course, quite frankly. That's for specialists, I believe. And I would like to end this excurs into history, all this kind of observation of how our knowledge progressed. I would like to end it on Bohr's model and I will probably spend maybe another lecture to be more specific about Bohr's model and some examples, etc. And that would be probably the level where I would like to stop. Contemporary physics is very important, very developed and moved much further than that. But it has so much information and it's not always well theorized, so to speak, characterized, not built into a system. There are many different facts and many different hypotheses about what's further. I'll probably say something about elementary particles, but not much, because it's a very, very wide area where many people are contributing their efforts. So that's it for kind of a basic introduction into the history of development of our view of our model. Again, we are researching our model. So this is a very simple introduction into the progress of our thoughts about what our matter is. All right, I suggest you to read the notes for this lecture. There are more names maybe mentioned than I did just for your general understanding. I would like you to feel that the whole thing is progressing and it's still progressing right now. We don't know what the nature actually is. We built the model, we made experiments and if they correspond to whatever kind of the theory corresponds to whatever we see in our experiments, then we are happy and then we move forward. Okay, thanks very much and good luck.