 Hi, I'm Zor. Welcome to Unisor education. We will talk today about nucleus of the atom Basically, it's kind of a again historical say about what actually happened how one discovery led to another discovery Not too much calculations or anything like that Now this lecture is part of the course called physics 14 is presented on unisor.com Well, it's a course basically it contains mechanics electromagnetic Chapter it has atoms like this one and and others So I do suggest you to watch this lecture from the website Unisor.com if you found it somewhere on YouTube or Somewhere else. It's just one lecture by itself But I think the value is in the course. So you take the course you take one lecture after another they are Positioned presented in logical order. There are menus which drive it The website also contains prerequisite Course called mass for teens Mandatory to learn physics absolutely The site is totally free. There are no advertisement So it's nothing nothing financial about this particular website So it's just pure knowledge and I do recommend you to use it to your full extent Plus there are some exams in some cases Which basically help you to realize how well you In control of the information again, you think you you can take these exams as many times as you want until you will get the perfect score okay, so We're talking about history basically right now history of Discoveries in in physics in particular about atom. So I will Touch briefly on few events Maybe a couple of comments basically and that's it. That's what that that's this lecture is about. I will introduce certain terminology Mentioned a few facts, but there is no theories primarily experimental physics and models Which physicists came up with is based on the experiments and gradually Coming to a point where we are well not right now, but we're in 1920s 1930s actually So one of the first thing which people have discovered and I didn't mention it before was experiment in 1897 Thompson English British Physicists discovered Electrons now His experiments were related to cathode rays so-called cathode rays, which means basically tube with positive and negative Connection into it and if you start Heating up the cathode with the negative connector Well, right now we know it meets electrons because electrons are getting excited and they're bumped out Because of the energy which is supplied by electricity the electrons are bumped out now if you have certain Detection and in this particular case detection of negative particles. That's exactly what Thompson that he discovered that from the cathode The rays which were emitted were negatively charged particles so that basically Started the whole thing and that was a discovery of electrons Now what happened later? So later he suggested that atom is basically like a positive soup with Electrons embedded in it Well, so probably it's not a good word. He suggested something like plum pudding If that what makes it better, whatever. Anyway, it's a solid basically mass with small negative Particles embedded in the positive environment so to speak pudding. Okay Next next was a very important person mentioned here Rutherford also British physicist Well, I have to really Tell that Rutherford was actually a whole school of brilliant physicist From from different countries by the way He built I think it was Manchester University He built a great team of people when he came as a professor of physics into this University and They were great Experimentalists, so they built certain devices which helped them to discover certain things now One of the first thing which his group Was involved was related to radioactivity the radioactive decay so-called It was observed that certain element like uranium or thorium or radium Emitted certain things Now they were trying basically to investigate what are these certain things and They have divided it into three categories alphabet and gamma rays Well, it turned to be much later that alpha rays were actually the nucleus of hello Which is a combination of two protons and two neutrons, but that was much later at that time It was just alpha rays, whatever it was beta rays Again later on it was discovered. It was basically electrons and Gamma rays are electromagnetic radiation of very high frequency very penetrating They have a shorter wavelengths than let's say divisible spectrum So these so-called rays alphabet and gamma rays were directed towards certain elements and Well, they saw what happens Now at that particular moment in time one of the experiments which The Rutherford was was actually conducting was he direct. He was directing alpha particles again as I'm telling later on it was positive nucleus nucleus of hello so directed alpha particles Through the gold foil very very thin gold foil and He discovered that Some of the particles just went through he detected on the other side with some apparatus and Some of them were basically deflected into different direction even into opposite direction So that brought him to a Planetary model of atom Because those particles which went through probably were like in between the nucleus and and the electron orbits and those which were reflected back were probably those who hit the nucleus itself and He was actually Been able to judge how many of them went through how many were reflected back and that gave them more or less some kind of idea about how much Geometrical space is occupied by nucleus and how much Is empty so he came up to the idea that atom is practically empty There is a very very small nucleus and there is and there are some electrons circulating around it that was his hypothesis planetary model and In between there is basically an empty space Now electrons are held by nucleus because nucleus must be positive them. So that's his Contribution he basically suggested that nucleus is inside the atom as a positively charged Particle if you wish electrons are negatively charged and they are rotating around Atom around nucleus of the atom. So that keeps them on the orbit I mean if they do not rotate they would just fall on the nucleus and basically the whole atom would collapse So that would contradict the stability of our matter of all the atoms So he suggested that electrons are circulating on orbits around nucleus and obviously the charge of nucleus must be equal to a sum of the charges of all electrons which are surrounding the nucleus and different Elements different elements actually Had different number of nucleus and that's why they have More charged in in the nucleus itself to keep so the charge should be The same of the same magnitude positive charge of nucleus should be of the same magnitude of some of the charges of all that negative electrons okay now he or Also suggested that nucleus of hydrogen Now we know that this is just one proton so nucleus of the hydrogen is present as part of nuclei of Other elements he was dealing with Which again in contemporary language means that the proton exists in every elements as a piece of the nuclear so that was his Well, I know suggestion or proof or that that's all experimentally proven What's next and then he also suggested that Inside the nuclear Might might be some other particles not just positively charged He called them neutrons But he actually said that these neutrons probably are coupled together proton and Neutron and and and electron sorry To come to a neutral particles, which he called neutron now that actually was not proven by any kind of experiment And it's not exactly true But it's it's an interesting hypothesis how he suggested that certain electrons are just not Surrounding on orbits, but they are coupled with some proton I don't think that the term proton was at that time actually used I think he was using a nuclear nucleus of hydrogen well, which now we know is the same so He was suggesting this new particle, which is actually a combo particle a couple of Two particles proton and and electron coupled together So nothing surround nothing is rotating around around anything else And they're also part of the of the nuclear nucleus Which did not turn out to be true But anyway the word neutron actually retained by physics and it was used later on when the real neutrons were discovered next Next was actually The discovery of neutrons by another British physicist Chadwick in 1932 So again, there are certain experiments he conducted and I'm not going into what kind of experiments They are really very sophisticated experiments to basically detect elementary particles such as such as neutron so in 1932 he suggested this and Immediately after that after the neutron as as a particle was discovered by Chadwick two physicists German Heisenberg and Russian Ivanenko came up with the model of the Nucleus as we know it right now as containing certain number of protons and neutrons So these are individual Building blocks of the matter Particles one particle is proton another particle is neutron and the combination of them both Actually created at nucleus of the atom how many of These protons and neutrons and electrons are in every element. Well, it's a different number different Elements have different number of protons neutrons and and electrons now To somehow Symbolically express This structure of the element they came up with notation as follows First there is a letter which is abbreviation of the name of the element So H stands for hydrogen for example, and then there are two numbers one number Is number of protons and number two is number of protons and neutrons By the way number of protons is equal to number of electrons. So that's basically describes the atom of hydrogen now What if I have hydrogen with one proton and one neutron making The total number of particles inside the nucleus to two so it's one proton and one neutron. Okay So that's basically kind of the same element, but not exactly the same So there is a term for this isotopes This is isotope So Hydrogen has a high and I said Isotope with one neutron with two with no there's no neutrons with one neutron and also there is a isotope with Two neutrons making the total number of three So this is called atomic number, and this is called atomic mass So total number of particles protons plus neutrons is called atomic mass in this case it's three for example and The number of protons which is equal to number of electrons is called atomic number and all elements Including their isotopes when the number of neutrons actually was different. They were basically constituting what Elements we deal with Okay Now Let me just give you a few examples By the way these isotopes of hydrogen have names For other elements, they're just different numbers that they have the same element Element name, but no different names for isotopes. This is called hydrogen. This is The terium and this is three two, but again, that's only for hydrogen Helium for example the general Helium Helium that's basically atomic numbers to atomic masses for because there are two Brotons and two neutrons usually and by the way the nucleus of helium is alpha particles as it was Discovered later on Now what else are the examples have carbon? six protons and six neutrons By the way, you see the number of protons and neutrons here and here is the same Two protons two neutrons making it for six protons and six neutrons making it well It's not necessarily true for other elements for example you have uranium for example you have 92 protons and one element is 235 Another isotope of uranium also 92 protons as 238 this is much more frequently occurring in in Earths basically and This one is a very rare one But it's this one which is used in atomic bomb and Whenever there are Mining the uranium it's usually this one and they're using certain process to convert this into this so they have basically fuel for atomic bombs Okay, so we have covered yet a couple of more examples This is gold our room in Latin it has 79 protons and The mess is 197. So the number of neutrons as you see is what one This is 118 right something like this 118 118 neutrons and 79 protons Different number as you see this is also different neutrons significantly more than protons Now and this is a very interesting point right now You see why electrons are on orbits around Nucleus is kind of understandable because nucleus is positively charged electrons are negatively charged and If they are rotating well, that's the electro static Force acts between positive and negative. They are attracting to each other, but because it's Rotating it it keeps the orbit Well, there is a problem with this planetary model which war introduced as I was previously talking about To overcome this problem, but in any case that's kind of understandable Now here is the question Protons are all positively charged So what holds together the nucleus because nucleus contains like 79 protons or 92 protons. Why aren't they that just repel each other and the whole basically business of Nucleus is just ending in this particular case Well, that was a problem which physicists Had to solve somehow so apparently Their theory was that there are some other forces Not only electrostatic forces Well, we have gravitational forces for example, right? So they came up with this idea that there are some other forces which act only on a very very short distance so the distance between protons inside the nucleus is Miniscule relative to the distance between protons and electrons So that's why these so-called strong forces between protons and protons and neutrons They are acting only within the nucleus. It's a nucleus specific forces and these forces always attract different particles Now what's other interesting thing is what's the role of neutrons? You see Without neutrons protons will be the only ones Which are located within the nucleus with Neutrons The strong forces between different particles still exist But protons are kind of diluted among neutrons and if neutrons are Embedded with protons in the same nucleus the distance between The protons becomes slightly greater than if they were just lumped together and that's why repel repelling forces electrostatic forces are a little bit Weaker when there is some distance you see the repelling forces obviously are much stronger the closer to each other are To positively charged protons, but they are just a little bit on the distance and there is a neutron between them The repelling electrostatic forces are smaller between these protons but the strong forces between proton and neutron and then neutron to proton are Existing and they're the same say this is the proton and this is neutron and this is another proton The repelling electrostatic forces are smaller than in this case in this case, right? So because there is a neutron and there is a distance between them, but the strong forces the nucleus Specific forces between this and this and between this are exactly the same as between and this and this and that's why the This is more stable so to speak nucleus and at the same time if you have certain deficiency of Neutrons it might have caused an easier Breaking of the nucleus under war by bombarding of this nucleus with certain Neutrons or alpha particles or something like that and That's probably one of the reasons why uranium 235 is easier to break Under attack of some neutrons for instance bombarding then uranium 238 because a couple of more neutrons really make you making a Nucleus a little bit more stable I mean obviously it all depends on the composition within the nucleus how they are organized, etc It's kind of a difficult Question and I don't think it's supposed to be part of your education right now The in internal structure of the nucleus. It's it's very very complex and apparently These are the so-called elementary particles like proton that neutron might Contain something within themselves as well something like nucleus contains protons and neutrons The protons contain something else. We'll talk about this in any case So what they would like to say is basically to introduce a new force in nature a force which exists between Pogicles inside the nucleus and That basically concludes my you know brief half historical Introduction into nucleus There are many very interesting stories about how certain discoveries were made how Rutherford, for example discovered neutrons and That that that not neutrons the protons and the planetary model how Chadwick discovered neutrons, I mean Experiments, I mean they people came up with these experiments. I mean nobody taught them how to do it They were researcher experimentalist physicists and They were looking for you know some proof of their theories. So that was extremely interesting It's a very creative process. I mean people don't probably realize How creative the real science actually is because you have no idea what exactly you're dealing with Until you will do some kind of research, etc So not only artists which are painting Some some pictures are are creative or or directors of movies physicists and mathematicians are very very creative people as well and That probably would be a nice end for this lecture. So read the notes for this lecture There are some maybe references to some website which which are good interesting stories And that's all on Unisor.com on the website So you go to atoms physics 14 scores atoms and within the atoms categories There is a chapter called building blocks of matter and that leads to this and other lectures Okay, thank you very much and good luck