 Hi, I'm Zor. Welcome to Inezor Education. I would like to start a new topic. It's about elementary particles, which are basically some construction blocks from which atoms are created. Now, this is the first lecture in this topic. It's called Main Particles. Now, this lecture is part of the course called Physics for Teens presented in Unizor.com. There is another course, by the way, on this website, Maths for Teens. It's a prerequisite. So, whether you take the course Maths for Teens or not, but you have to know what's in it, because the physics without math is nothing. You don't even have to sign in if you don't want to. Now, there is some functionality which is related to signing in, but that's beyond the point. It's all explained in some introductory articles on the website. Now, the course on the website is basically organized in a series of hierarchical menus. Now, each lecture has a textual supplement, basically like a textbook. There are problem solved, there are exams, which you can take as many times as you want until you will get perfect scores. So, I do suggest you to use the website rather than, let's say, YouTube channel or anything else where you can find this lecture. So, Main Particles. Well, the history of physics is basically digging deeper and deeper into the structure of the matter. Well, in some way. Now, first of all, people have discovered molecules which basically retain certain chemical properties and physical properties of matter. Then they found out that molecules are actually compositions of atoms. Well, then they started digging the atoms. And three main particles actually were, well, in the beginning of this process of discovery, what is atom? It's electrons, protons and neutrons. Now, a couple of words about these particles. Well, first of all, they are kind of main particles because they are main building blocks of matter. There are many other particles. And there is a whole story about how we can put them into some kind of a nice theory, structure, whatever. And we will talk about certain structures. But in any case, these three which I will talk about today, electrons, protons and neutrons are still considered to be the main particles, main elementary particles. Now, are they the end of the way, the end of the road? And there is nothing inside these main particles? Well, apparently there are certain other theories and experiments that basically show that it might be not. It's not as conclusive I would say as the existence of these three main particles is kind of conclusive. But their inner structure, well, again, I don't want to talk about this right now. I will probably spend some time basically explaining what's the theory behind the structure of these elementary particles. So today we will talk about just these three. Now, basically whatever I'm discussing right now is already kind of touched in different places in the previous lectures. Well, maybe just very briefly. Electrons were discovered in experiments by Thompson at the end of the 19th century. Basically it's cathode tube, so to speak. So you have a tube, you have plus and minus contact inside the tubes and the problem is that the, let's say, cathode is hot, for example, then we know right now that it emits electrons. Well, he didn't know that, but he did understand that there is a current which is going through this circuit because electrons from the negative end of this tube are emitted because it's a hot cathode and they are going into the positive end of the tube. Now, the problem is that if you have certain different shapes of the positive side and if you have something like a electrostatic field around it, then the cathode ray is actually deviated and because he detected this type of deviation he concluded that there are some material particles which are carried with negative charge and that's basically the beginning how the electrons were actually discovered. Now, speaking about protons, that was a little differently and there are many people actually who did some experiments which contributed to the discovery of the protons and obviously subsequent discoveries were using something which has already been discovered before. Well, probably one of the, I would say, decisive points was also a tube with some gas. The gas can be different, can be helium, can be hydrogen, can be neon, I mean different gases that were experimented. Now, what they did was they put the cathode with holes. This is the cathode which is minus. Now, this is plus. Now, here they put some fluorescent material and what's interesting is that with the high voltage well, they have already kind of known that electrons are basically going this way. However, what happened was that this luminescent kind of cover or whatever it is material started imaging light. So, they have suggested that probably electrons as they're coming to this hit the molecules or atoms of gas, whether it's hydrogen or helium or something like this. And what happened now, the atom is neutral so basically the electrons and they're coming here, they hit the atoms of the gas and after that, certain electrons were basically kicked out of these atoms and also go to the positive end of the tube. What remains was the positive. Since electrons were this way, what remains in the atoms of this gas, the positive part. And the positive part was gravitating towards negative end of the tube but since there are holes, some of them went through and lit the luminescent material. So, there are some positive particles as a result of this bombardment of the gas. Now, these positive particles were different for different gases because they can just detect certain amount of luminosity Also, if you put something like an electrostatic field around this part of the tube, then you would change the direction of these positive particles. So, the combination of this and some other experiments actually came to conclusion that there are these positive particles. Now, then there was planetary model of the atom of Rutherford then Bohr came into Bohr's model which is kind of enhancement of the Rutherford. We did talk about this before. And Rutherford experiments proved that the positive site, which is in the nucleus, and the atom is practically empty because he was experimenting with gold foil. We were talking about this before and the particles went just through the atoms. Now, what is interesting is there was experiments with which proved the existence of neutron. Now, this was done in 1930s by Chadwick the English British physicist So, his experiments were he was bombarding beryllium with certain, well, rays which are coming from radioactive material. I think he was using polonium. And as a result he basically saw that the particles which were emitted by radioactive polonium bombarded beryllium and kicked out from beryllium some particles, material particles, which he has detected but they were neutrally charged. It's not positive, it's not negative. So, he came to a conclusion that there is some other particle and he called it neutron. Now, what's also interesting is that experiments show that atom is practically empty, so to speak. The size of the atom is about 10 to the minus 10 meters. Well, I put this order off, which means it can be 1.0, or it can be 5.0 times this multiplier. But anyway, it's some kind of relatively small multiplier, let's say from 1 to 9, something like this, times 10 to the minus 10 meters. Whereas, the nucleus has 10 to the minus 15 meters. So, the size of the nucleus is 5 orders of magnitude. 5 orders of magnitude is 100,000. So, the nucleus is about, well, not necessarily, different nucleus have different ratio. Some of them have 20,000. Some of them have 100,000. But it's significantly smaller than the size of the entire atom. So, that's why atom is practically empty. At the same time, the mass of the atom is basically concentrated in the nucleus. Nucleus has something like 99.9% of the mass. So, electrons are very, very light. And all the mass is in nucleus. Now, it was later discovered that neutrons and protons are about the same weight and size. The difference is something like 110 to 1%, something like this. But neutrons are neutral and protons are positive. Now, number of protons is equal to number of electrons to keep the atom neutral. And it's called atomic number Z. Number of neutrons, which is usually letter A. Now, their sum is atomic mass. Now, what we have learned before that chemical properties depend on electrons. How they are organized into shells and sub shells. And do you remember we were talking about some chemical reactions in the previous lectures. So, number of protons and number of electrons is the same. And they determine, so Z the atomic number determines chemical properties of atom. So, what about N? Can we have different number of neutrons for the same number of protons? And there is yes. Now, there are so-called isotopes of the same material. Like, for example hydrogen is, generally speaking, only one proton in the nucleus. But it has isotope with one neutron. So, proton and neutron. And it has another isotope with two neutrons per one proton. So, they terium and tritium they are called. And many different elements have their isotopes. For example, uranium has two known isotopes. Uranium 235. That's the mass. That's A 235. And there is 238. Where Z is the same thing. I don't remember exactly. Maybe it's 92. So, it's different number of neutrons. Now, here is more I would say physical aspect of this. Obviously electrons are surrounding the nucleus. And they're not flying, not freely flying away. I mean, sometimes they do. But generally speaking, the atom is holding itself. Now, why? Well, the protons are positive. Electrons are negative. They are surrounding on some orbits. And their electron, positive and negative, keeps electrons on their orbits. Now, the protons among themselves in the nucleus, they are all positive. Which means they repel each other. So, what keeps the nucleus together? Okay. I think I mentioned it once, but I'll mention it again. There are certain forces in nature which are, number one, act on a very, very short distance. The distance of the size of the nucleus. Number two, they are much stronger than electrostatic forces of repelling. So, these strong, or strong is the name, by the way, strong forces or nuclear forces. So, these forces actually keep protons together. So, electrostatic forces are trying to repel protons and destroy the nucleus. The strong nuclear forces they are keeping it together. Now, existence of neutrons actually adds strength into the nucleus. Because neutrons are neutral. They are not positive. So, they are not really repelled by electrostatic forces. But the strong forces do exist. Strong forces exist between any particles inside the nucleus. Between proton and proton, between proton and neutron, between neutron and neutron. So, all these strong forces keep the nucleus together. Well, unless, of course, we bombard the nucleus of the atom with some other particles which basically breaks it apart. But that's a different story. Under normal circumstances strong or nuclear forces keep these nucleus together. And basically that's everything I wanted to talk about today. Yeah, one other detail. Speaking about mass. Now, I was talking about the whole mass, like 9.9%, is concentrated in the nucleus. Now under some circumstances, as I was just talking before, the nucleus can be broken. Like, after bombarding it with some particles. The parts will also have certain mass, obviously. Now, well from our non-relativistic standpoint, the mass of the all pieces into which the nucleus has been broken should be equal to the initial mass of the nucleus. Well, that's not necessarily true. And the reason is that the energy which keeps the nucleus together according to a famous Einstein formula, the energy has certain mass. And when we break this nucleus using some kind of an outside bombardment or whatever you might not have necessarily the sum of the pieces is equal to the initial mass. And that's because the energy is involved here. Energy which keeps it together. Or energy which breaks them apart, etc. So there is certain difference between them. And we will talk about this atomic bomb actually is built on this formula so to speak. But that's a different lecture in some other later time. So far, I just suggest you to read the notes for this lecture. So you go to Unisor.com choose physics for gene course. This part is called atoms. And within the atoms, I think there is a certain topic which is called elementary particles and the first lecture in this topic is about main particles which is electron, proton and neutron. They are main. And we will talk about some others. Well, that's it for today. Thank you very much and good luck.