Understanding the Structure of Atoms

Hey all welcome to home school and we are with class 11 chemistry and I am starting with the second chapter of class 11 that is structure of atom already I have completed the first unit that is basic concepts of chemistry its link is provided in the description if you have not it watched please go and watch and coming to this chapter structure of atoms one of the very important chapters of 11th chemistry where the competitive questions can be asked from this particular chapter and but it's a very simple chapter most of the aspects from the chapter you have been studied in your schooling also but then it's like a deeper version of those concepts definitely you have to concentrate this chapter for competitive point of view like for NEET, JEE etc. Yeah, so I would be explaining each and every concept that is there in your NCIT textbook along with that few questions let me solve here and there regarding competitive topics. Okay, so starting with the chapter first I'll be telling you what you are actually studying in a chapter. See structure of atom right. And you must have heard about the Dalton's theory, which we have studied in the first chapter. He told one important point that each and every matter is made up of small particles. We call those particles as atoms. Right. And we get numerous chemical compounds. We can prepare lots of chemical compounds. E is due to. The combination of atoms. When two atoms combine, we say it is a chemical reaction. So when two atoms of different elements combine, a new substance is formed. This process is called as chemical reaction. We all know this. And he told one point that atom cannot be divided further. Atom is the smallest particle of element or matter. which cannot be divisible okay but but in the 19th century people started studying about the atom because this is the magic guy which is there in the matter on combination of these magic guys you get new new substances so they wanted to study deeply about this particular atom And there started discovery of subatomic particles. People found that atom do has certain particles in it. Okay, microscopic particles in it. Very, very small. And they will decide the characteristic of atom. They will decide the properties of atoms. They called these particles within an atom. subatomic particles okay so initially in a chapter we will study about discovery discovery of subatomic particles so what are subatomic particles so they are the particles that are present inside the atom okay so there are electrons neutrons and protons mainly inside the atom And we are studying how electrons were discovered, how protons were discovered, how neutrons were discovered. So this entire class is about the discovery of electrons, protons and neutrons. And after this, you will study various atomic models in the chapter. OK, so you will study various atomic models. That means once you know that there are. these subatomic particles present in the atom and you must also have an idea about how these particles are arranged in the atom. So exactly where they are located in the atom. So how small is the atom? Okay. What is the shape of an atom? Where are the subatomic particles and how they are arranged? You know, this is what explained by various atomic models. Okay. So the first atomic model we study is very basic one that is Thomson's atomic model. Very simple one. And after that we study Rutherford's atomic model. So both the models I think you have studied in your schooling right in class 9. And later comes your Bohr's atomic model. And finally comes your quantum mechanical model. Quantum model of an atom. Okay, so finally quantum model of an atom is the accepted model for the structure of atom. So based on quantum mechanical model we decide like how electrons are present, where they are present and how they revolve around the nucleus. So everything was well explained and lots of justification was given for this quantum mechanical model. And Before quantum mechanical model these were the models but that had given little idea about the structure of an atom. So all of them also we have to discuss. And there are many developments you know before the Bohr's model there came a discovery of electromagnetic radiation, atomic spectra, hydrogen spectra you know by learning all these experiments Bohr has introduced his models. we are learning those developments also okay so here we will learn something called developments towards bool's model at the same time before we go for quantum model we do learn certain developments we do learn certain discoveries like hansenberg's principle uh you know d broglie wave equation and all of them so based on these developments based on these discoveries you know people started inventing this quantum mechanical model of an atom so those developments also we will discuss before we discuss quantum models so this is all about the various things you will discuss in the chapter okay fine so quickly without wasting much time today's topic let us discuss that is discovery of subatomic particles okay so initially I will go with the discovery of electrons. So let us discuss about discovery of electrons. Fine. So the first question that comes to our mind is who discovered these electrons? So it is the scientist J.J. Thompson. J.J. Thompson discovered electrons. And he discovered electrons by a very special experimental setup that is by cathode ray discharge tube. Okay. So he used which experiment for the discovery of electrons? He used cathode ray discharge tube. discharge tube experiment okay through this experiment through this instrument he actually discovered electrons and let us see what is this cathode ray discharge tube and how he has conducted the experiment okay fine and coming to this cathode ray discharge tube it is just a glass tube okay it is just a glass tube glass tube right and which had a two electrodes in it two metal plates you will observe in this glass tube okay and one metal plate is connected to negative terminal of battery and the other metal plate is connected to positive terminal of battery. So this is a negative terminal and this is a positive terminal of battery. Okay. Say the one which is connected to negative terminal is called what cathode isn't it? And the one which is connected to positive terminal of battery is called anode. So these are the two metal plates connected to negative and positive terminal. So respective to that I will call this as cathode and this as anode. So this is a very basic experimental setup. And you know, the voltage that is supplied to this system is very much high. You know, he has used around 10,000 volts of voltage for his experiment. So how much is the voltage? Remember this number. This is very, very important. Okay, 10,000 volts of voltage has been supplied. You know? to this particular tube fine and you know he filled the cathode ray tube with hydrogen gas okay or you can simply take it as a vacuum also okay you can simply consider vacuum inside the glass or you can consider the very lighter gas that is hydrogen very little amount of hydrogen gas he took or it can be vacuum also Okay and you know what he maintained very very less pressure. Okay so very very less pressure. Okay so this was his experimental setup. Not only that he coated this end. Okay or or you will find the entire glass coated with coated with zinc sulfide. You will have zinc sulfide coating. Especially this end. Especially this end. Okay. So what is the use of zinc sulfide coating? You know what? This zinc sulfide coating will act as a fluorescent material. It will act as fluorescent material. So what do you mean by fluorescent material here? Just it glows. You know when something, some rays or some particles fall on fluorescent material, it will glow. Okay, so that is the nature of zinc sulfide material. Clear? So this is his experimental setup. And now let us see what he has observed in his experiment. You know what suddenly? He started observing certain rays, certain rays coming from cathode to anode side. Okay, so what did he observe? He observed certain rays coming from cathode to anode. and they're actually these rays are made up of invisible particles these rays are made up of very small particles which you cannot see with your eyes actually speaking you cannot see these rays with your eyes that is the reason that is the reason he coated the glass tube with zinc sulfide because when something falls on zinc sulfide it will glow right that's how you will come to know whether something is coming something there in a glass tube or not or you will also find out from where to where they are going isn't it so the moment he supplied high voltage maintaining less pressure he started observing glow at zinc sulfide end okay where did he coat the zinc sulfide towards anode at this end so the moment he observed a glow at zinc sulfide end he confirmed that There must be some rays coming from cathode to anode. That's the reason he has observed glow in the zinc sulfide coating. Clear everyone? So this is a proof that you know the rays are coming from cathode to anode. Actually when he held the electric field or magnetic field. You know these rays started deflecting towards the positive side of electric field. The positive side of magnetic field. That means it confirms that they do have charge and which charge they have? Yes, definitely they have a negative charge. When they are deflected towards positive terminals of electric field and magnetic field, definitely they must be carrying negative charge, isn't it? So that's how he came to know that they are negatively charged. See on all these observations he has given certain characteristics of cathode rays. We will discuss about cathode ray characteristics. And actually these rays he did not call with the name electrons. Initially, he called it with cathode rays. Okay, so that's why I'll also call them with cathode rays. Let us see those characteristics. Before that, let us see an experiment that how the rays will travel from cathode to anode and how the zinc sulfide end will glow and all that with one very, very beautiful visual. Clear? This is the setup of cathode ray discharge tube. You can see a discharge tube that is connected to high voltage battery. Right. And now when the high voltage is supplied, just watch the observation. See how the cathode rays pass from cathode to anode. so see he will on the switch so high voltage is supplied to this glass tube and you can very nicely see the rays right that is there inside the glass tube discharge tube so this is how cathode rays are passing from cathode side to anode side clear and the rays travel in a straight line right and they are these rays are made up of so many small invisible particles that's the reason the glass tube is coated with zinc sulfide so you are actually observing a glow you on a glass tube and you can able to see the rays just because of zinc sulfide coating you can able to see the rays here and now he is holding a magnet onto this see the deflection of rays see magnetic field is introduced near the rays they are deflecting before they were traveling in a straight line but now they are deflecting right so this deflection shows that the rays carry a charge okay and you can see the rays were deflecting to this angles now so they are having a charge It's a negative charge. Okay, so the deflection is towards the positive side of electric and magnetic field. So this is a small experiment of cathode ray discharge tube where you can observe the deflection on introducing magnetic and electric field and you can also observe the rays are traveling in a straight line. Okay, so that's all about cathode ray experiment. so it was a beautiful experiment isn't it so now that you understood how the cathode rays move from cathode to anode and how they get deflected towards the positive side of magnetic field and electric field isn't it and now let us list it out all the characteristics characteristics of cathode rays okay see here Coming to the first characteristic, it's very simple. These rays, these rays travel in straight line. Okay, so how do they travel? They travel in straight line. You have observed the, you know, the rays traveling in a straight line even in the experiment, isn't it? So, what do I write here? They travel in straight line. Clear? Very, very important characteristic. And these rays carry a charge. They carry a negative charge. Isn't it? And how do you confirm that they carry a negative charge? It is due to they deflect. They deflect towards positive side of electric and magnetic field. Isn't it? electric and magnetic field and this confirms that these rays are carrying a negative charge right so very very important point and one more very very important point is the characteristics or the properties of these rays okay do not depend on nature of gas whatever may be the gas you take you know they have the same properties they have a same negative charge and they travel from cathode to anode and they travel in a straight line they reflect towards the positive side of electric and magnetic field that characteristics remain same whichever the gas you take inside the discharge Okay, so what I will write here is properties of very very important properties of these rays. These rays do not depend on do not depend on nature of gas. Really very important point. Whatever may be the gas, whatever may be the material inside electrons are electrons only. okay say electrons of hydrogen is same as electrons of oxygen which is same as electrons of nitrogen gas which is same as electrons of helium gas okay so all electrons in all the elements in all the atoms is always similar they do have same properties okay so that is what the meaning of the last point so these are the basic characteristics of cathode this and later why do we call them as cathode rays because they emerge from cathode okay they they come from cathode say they called it as cathode rays and later the name was replaced by electrons clear fine and now we will study about charge to mass ratio of an electron guys really very important concept charge to mass ratio uh j j thompson again this was discovered by a person gg thompson he has given a value for charge to mass ratio actually through this value we could able to find out the charge of an electron as well as the individual mass of an electron okay so let us see what experiment he has conducted and how he found the charge to mass ratio of an electron see he took a glass tube the same setup here the glass tube he has taken and he connected uh two two electrodes right he connected one to negative terminal the other one to positive terminal okay you all know that electrons will start coming from cathode side to anode side right so this is our cathode and this is our anode okay and now he made a hole uh you know through this anode he made a hole in the anode so that you can see the anode and you can see the anode and you can see the anode and you can see the the rays can pass through the anode isn't it they will come from cathode and the rays he wanted to get passed out of this instrument so he made a hole here he made a hole here so the rays are coming through the hole okay so when the rays were coming okay so this is one ray one ray of electrons which is coming out through the anode and you know what uh he kept a zinc sulfide scream here he kept a zinc sulfide screen. So this is our zinc sulfide screen. See guys when you don't have any electric and magnetic field here they do travel in a straight line and definitely they will hit at this point. Let me call this point as A. Okay say when there was no electric and magnetic field only when those fields are there they get deflected. Their direction gets deviated and they deviate that. towards the positive side of electric field and magnetic field. Yes or no? Because they are negatively charged. Fine. So, when you do not have anything, they would travel in a straight line. Fine. And now, I will keep some electric plate. Okay. And here, it is a positive terminal and this is a negative terminal. Okay. So, I have introduced electric plates, positive terminal, negative terminal. And now can you all imagine if a ray went travel and come out and where does this ray, how does this ray deviate? How does the direction of this ray changes? Definitely its direction is towards the positive terminal of a plate. Yes or no? Since the ray is negatively charged, the ray would deviate. It will direct itself towards the positive plate of electric field. Right. so that's how you will find the deflection uh in the ray in the race direction and it will hit at a point b it will not go straight it doesn't hit that point a now it will hit at point b on a zinc sulfide plate right okay so now let me introduce and now i will take it out i will take out this electric field okay uh i'll take out the electric wind and i'll add a magnetic field Okay, so let me take a magnetic field and this is a south pole and this is a north pole. Consider south pole as positive, north pole as negative. Okay, and now when the ray comes. When a ray comes, something like this, it is coming and definitely it will show the deflection towards the positive side of the magnet and it will hit on a zinc sulfide plate at a point C. Isn't it? Yes. So when magnetic field is there, definitely the ray would deviate towards the positive side of magnet and it is hitting at point C. Isn't it? Okay. So now I will introduce both electric field and magnetic field. okay so this is our electric field positive terminal acr and this is our negative terminal of electric field so magnet this is a positive terminal this is a negative terminal now imagine if a ray is passing okay if a ray passing and when it comes at this point can you tell me in which direction will it deviate both electric field magnetic field is there positive terminal of electric field is this side you positive terminal of magnetic field is this side now the negative charge carrying ray is coming so where will it direct here also positive charges are here also positive charges the stronger one okay so the ray will not deviate anywhere the ray definitely will pass straight it will go in a straight line and it will hit at point a it will hit at point a right so when only electric field was there deviation you would observe When only magnetic field was there, deviation you have observed. When both electric and magnetic fields are there in opposite direction, right? With opposite poles, then definitely the ray will not deviate anywhere. It will go straight and it will hit at point A. See guys, this is the experiment he conducted and based on his observation, based on his observation, Okay, so what did he observe? What did he observe? Okay, that is based on the amount of deflection the amount of deflection by cathode rays by cathode rays when electric and magnetic fields were kept Okay magnetic fields were kept okay so it must have deviated to certain angle and he calculated the angle of deviation and how much of ray has got deviated to how much extent you know all that he observed and based on that observation he has calculated He has calculated charge by mass ratio of an electron and he got a value as 1.75 into 10 power 11 coulomb per kg. Okay. So this is the value you have to remember. Charge symbol is E, mass symbol is M. Okay. So this is charge by mass ratio of an electron. Clear? So you no need to worry about how he got this value. You will study it in higher classes. So that is not necessary. Just try to understand the experiment and based on the amount of deflection like to which extent the direction of rays are changing and where they are hitting on zinc sulfide screen all that he carefully studied experimentally and by applying lots of mathematics. He calculated this value and he told this value is nothing but the charge to mass ratio of an electron. Okay, so this is really an important value to remember. Clear? Fine. And now, here one more thing he observed was the deflection. Okay, the amount of deflection. The amount of deflection was... dependent on was dependent on three factors dependent on three factors guys okay let us discuss what are the three factors on which the deflection you know by looking at the amount of deflection he calculated this value but that amount of deflection the way the direction of race changed was dependent on three factors okay let us see what are those three factors first one amount of deflection amount of deflection was greater was greater when Magnitude of charge was greater. When magnitude of charge was greater. Okay, that means when the rays were carrying lots of negative charge, then he has observed lots of deflection in the ray, okay, towards the positive side of electric and magnetic field. So greater the magnitude of charge, greater was the deflection. That is what the meaning of the first point. And coming to the second point, greater the field strength. Greater the field strength or let me write this way. Greater the strength of electric and magnetic field. Electric and magnetic field. Greater was the deflection. Greater was the deflection. Okay. So this is another factor. Say the more strength you give, the more deflection you will find in the experiment. Okay, so that is what the meaning of the second point and coming to the third point. The third point says lighter the mass, lighter the mass of particles, particles, more was the deflection. More was the deflection. Okay, it definitely, logically speaking, this makes a sense, right? Anything which is lighter in weight will deflect to a larger extent. Since electrons are very lighter in mass, they would have deflected to this much extent, right, when electric and magnetic fields were kept. So, these were the three more observations he has made based on his experiment. So, based on these observations and you know, By applying lots of mathematical applications and knowledge, he arrived at this particular value for charge to mass ratio. Clear? So this is all about charge to mass ratio. And after that, there is a person called Millikan. So by Millikan's oil drop method, we can find the charge of single electron. Okay. So charge of an electron was found by Millikan's oil drop method. Once you know the charge of electron, charge by mass ratio of an electron, you can easily find the mass of an electron, right? So let us see how we can find the mass of an electron. See guys, separate video I will make on Millikan's oil drop method like what experiment he conducted, how he conducted and how he can calculate the charge of single electron and everything. I will do a separate video on that. Now just try to remember charge of an electron. Charge of an electron was found to be this. I mean it is minus 1.6 into 10 power minus 19 coulombs. So this is the charge of one electron. And this was found by Millikan's oil drop method. okay so don't worry i'll make a separate experiment okay separate video about this particular experiment clear so just remember the value charge of one electron is always minus 1.6 into 10 power minus 19 coulomb okay so now you know charge of an electron charge by mass ratio of an electron you know can't you find out mass of an electron so definitely so uh We all know charge by mass ratio. Okay, so how much is the value? It is 1.75 into 10 power 11 coulomb per kg. Okay, and we know charge of an electron. So in the numerators value, I know, right? So what is the charge of an electron? It is this much that is 1.6 into 10 power minus 19 coulomb. Actually, it is minus there is no significance for minus sign here. No need to take a sign just take a value, right? So divided by mass. is equal to 1.75 into 10 power 11 coulomb per kg right so i want to find out mass here so mass is equal to how do you do 1.6 into 10 power minus 19 coulomb divided by this comes here so 1.75 into 10 power 11 coulomb per kg right so uh this this coulomb coulomb gets cancelled you And on calculating this, you will get mass of electron. So how much is mass of electron? It is 9.1 into 10 power minus 31 kg. Isn't it? So this value is really very important value for calculating any numerical. Okay. So here three values are important to remember. One is mass of electron. that is 9.1 into 10 power minus 31 kg another important point is charge of an electron is this much found by millikan's oil drop experiment and charge to mass ratio of an electron is this much 1.75 into 10 power 11 coulomb per kg okay so these are the three important values one must remember for calculating any numericals okay so whichever may be the gas whatever may be the electron electron may be there in whatever element okay charge to mass ratio remains common okay so because we all have studied the property of electron doesn't depend on nature of gas or nature of element right so whatever may be the element charge to mass ratio of electron is always this okay fine and charge of an electron mass of an electron. These are the constant values that you have to remember. So this is all about the discovery of electrons. So we studied how electrons were discovered. We studied how charge to mass ratio was discovered and we also studied how to get a value for mass of an electron. Okay so with this I will complete this video and in my next video let me talk about discovery of protons and discovery of electrons and also I will come up with few challenging questions that can be asked on this concept. Clear? That's all about today's session. We will meet up in the next session and do subscribe our channel to learn the concepts in a easiest way and in a detailed way. Thank you so much.

He told one important point that each and every matter is made up of small particles. We call those particles as atoms. Right.

And we get numerous chemical compounds. We can prepare lots of chemical compounds. E is due to.

The combination of atoms. When two atoms combine, we say it is a chemical reaction. So when two atoms of different elements combine, a new substance is formed. This process is called as chemical reaction. We all know this.

And he told one point that atom cannot be divided further. Atom is the smallest particle of element or matter. which cannot be divisible okay but but in the 19th century people started studying about the atom because this is the magic guy which is there in the matter on combination of these magic guys you get new new substances so they wanted to study deeply about this particular atom And there started discovery of subatomic particles. People found that atom do has certain particles in it.

Okay, microscopic particles in it. Very, very small. And they will decide the characteristic of atom. They will decide the properties of atoms. They called these particles within an atom.

subatomic particles okay so initially in a chapter we will study about discovery discovery of subatomic particles so what are subatomic particles so they are the particles that are present inside the atom okay so there are electrons neutrons and protons mainly inside the atom And we are studying how electrons were discovered, how protons were discovered, how neutrons were discovered. So this entire class is about the discovery of electrons, protons and neutrons. And after this, you will study various atomic models in the chapter. OK, so you will study various atomic models. That means once you know that there are.

these subatomic particles present in the atom and you must also have an idea about how these particles are arranged in the atom. So exactly where they are located in the atom. So how small is the atom?

Okay. What is the shape of an atom? Where are the subatomic particles and how they are arranged?

You know, this is what explained by various atomic models. Okay. So the first atomic model we study is very basic one that is Thomson's atomic model.

Very simple one. And after that we study Rutherford's atomic model. So both the models I think you have studied in your schooling right in class 9. And later comes your Bohr's atomic model.

And finally comes your quantum mechanical model. Quantum model of an atom. Okay, so finally quantum model of an atom is the accepted model for the structure of atom. So based on quantum mechanical model we decide like how electrons are present, where they are present and how they revolve around the nucleus.

So everything was well explained and lots of justification was given for this quantum mechanical model. And Before quantum mechanical model these were the models but that had given little idea about the structure of an atom. So all of them also we have to discuss.

And there are many developments you know before the Bohr's model there came a discovery of electromagnetic radiation, atomic spectra, hydrogen spectra you know by learning all these experiments Bohr has introduced his models. we are learning those developments also okay so here we will learn something called developments towards bool's model at the same time before we go for quantum model we do learn certain developments we do learn certain discoveries like hansenberg's principle uh you know d broglie wave equation and all of them so based on these developments based on these discoveries you know people started inventing this quantum mechanical model of an atom so those developments also we will discuss before we discuss quantum models so this is all about the various things you will discuss in the chapter okay fine so quickly without wasting much time today's topic let us discuss that is discovery of subatomic particles okay so initially I will go with the discovery of electrons. So let us discuss about discovery of electrons.

Fine. So the first question that comes to our mind is who discovered these electrons? So it is the scientist J.J. Thompson.

J.J. Thompson discovered electrons. And he discovered electrons by a very special experimental setup that is by cathode ray discharge tube. Okay.

So he used which experiment for the discovery of electrons? He used cathode ray discharge tube. discharge tube experiment okay through this experiment through this instrument he actually discovered electrons and let us see what is this cathode ray discharge tube and how he has conducted the experiment okay fine and coming to this cathode ray discharge tube it is just a glass tube okay it is just a glass tube glass tube right and which had a two electrodes in it two metal plates you will observe in this glass tube okay and one metal plate is connected to negative terminal of battery and the other metal plate is connected to positive terminal of battery.

So this is a negative terminal and this is a positive terminal of battery. Okay. Say the one which is connected to negative terminal is called what cathode isn't it? And the one which is connected to positive terminal of battery is called anode.

So these are the two metal plates connected to negative and positive terminal. So respective to that I will call this as cathode and this as anode. So this is a very basic experimental setup.

And you know, the voltage that is supplied to this system is very much high. You know, he has used around 10,000 volts of voltage for his experiment. So how much is the voltage? Remember this number. This is very, very important.

Okay, 10,000 volts of voltage has been supplied. You know? to this particular tube fine and you know he filled the cathode ray tube with hydrogen gas okay or you can simply take it as a vacuum also okay you can simply consider vacuum inside the glass or you can consider the very lighter gas that is hydrogen very little amount of hydrogen gas he took or it can be vacuum also Okay and you know what he maintained very very less pressure.

Okay so very very less pressure. Okay so this was his experimental setup. Not only that he coated this end.

Okay or or you will find the entire glass coated with coated with zinc sulfide. You will have zinc sulfide coating. Especially this end. Especially this end.

Okay. So what is the use of zinc sulfide coating? You know what?

This zinc sulfide coating will act as a fluorescent material. It will act as fluorescent material. So what do you mean by fluorescent material here?

Just it glows. You know when something, some rays or some particles fall on fluorescent material, it will glow. Okay, so that is the nature of zinc sulfide material.

Clear? So this is his experimental setup. And now let us see what he has observed in his experiment. You know what suddenly? He started observing certain rays, certain rays coming from cathode to anode side.

Okay, so what did he observe? He observed certain rays coming from cathode to anode. and they're actually these rays are made up of invisible particles these rays are made up of very small particles which you cannot see with your eyes actually speaking you cannot see these rays with your eyes that is the reason that is the reason he coated the glass tube with zinc sulfide because when something falls on zinc sulfide it will glow right that's how you will come to know whether something is coming something there in a glass tube or not or you will also find out from where to where they are going isn't it so the moment he supplied high voltage maintaining less pressure he started observing glow at zinc sulfide end okay where did he coat the zinc sulfide towards anode at this end so the moment he observed a glow at zinc sulfide end he confirmed that There must be some rays coming from cathode to anode.

That's the reason he has observed glow in the zinc sulfide coating. Clear everyone? So this is a proof that you know the rays are coming from cathode to anode.

Actually when he held the electric field or magnetic field. You know these rays started deflecting towards the positive side of electric field. The positive side of magnetic field.

That means it confirms that they do have charge and which charge they have? Yes, definitely they have a negative charge. When they are deflected towards positive terminals of electric field and magnetic field, definitely they must be carrying negative charge, isn't it? So that's how he came to know that they are negatively charged. See on all these observations he has given certain characteristics of cathode rays.

We will discuss about cathode ray characteristics. And actually these rays he did not call with the name electrons. Initially, he called it with cathode rays. Okay, so that's why I'll also call them with cathode rays. Let us see those characteristics.

Before that, let us see an experiment that how the rays will travel from cathode to anode and how the zinc sulfide end will glow and all that with one very, very beautiful visual. Clear? This is the setup of cathode ray discharge tube.

You can see a discharge tube that is connected to high voltage battery. Right. And now when the high voltage is supplied, just watch the observation.

See how the cathode rays pass from cathode to anode. so see he will on the switch so high voltage is supplied to this glass tube and you can very nicely see the rays right that is there inside the glass tube discharge tube so this is how cathode rays are passing from cathode side to anode side clear and the rays travel in a straight line right and they are these rays are made up of so many small invisible particles that's the reason the glass tube is coated with zinc sulfide so you are actually observing a glow you on a glass tube and you can able to see the rays just because of zinc sulfide coating you can able to see the rays here and now he is holding a magnet onto this see the deflection of rays see magnetic field is introduced near the rays they are deflecting before they were traveling in a straight line but now they are deflecting right so this deflection shows that the rays carry a charge okay and you can see the rays were deflecting to this angles now so they are having a charge It's a negative charge. Okay, so the deflection is towards the positive side of electric and magnetic field.

So this is a small experiment of cathode ray discharge tube where you can observe the deflection on introducing magnetic and electric field and you can also observe the rays are traveling in a straight line. Okay, so that's all about cathode ray experiment. so it was a beautiful experiment isn't it so now that you understood how the cathode rays move from cathode to anode and how they get deflected towards the positive side of magnetic field and electric field isn't it and now let us list it out all the characteristics characteristics of cathode rays okay see here Coming to the first characteristic, it's very simple. These rays, these rays travel in straight line. Okay, so how do they travel?

They travel in straight line. You have observed the, you know, the rays traveling in a straight line even in the experiment, isn't it? So, what do I write here? They travel in straight line.

Clear? Very, very important characteristic. And these rays carry a charge.

They carry a negative charge. Isn't it? And how do you confirm that they carry a negative charge?

It is due to they deflect. They deflect towards positive side of electric and magnetic field. Isn't it? electric and magnetic field and this confirms that these rays are carrying a negative charge right so very very important point and one more very very important point is the characteristics or the properties of these rays okay do not depend on nature of gas whatever may be the gas you take you know they have the same properties they have a same negative charge and they travel from cathode to anode and they travel in a straight line they reflect towards the positive side of electric and magnetic field that characteristics remain same whichever the gas you take inside the discharge Okay, so what I will write here is properties of very very important properties of these rays. These rays do not depend on do not depend on nature of gas.

Really very important point. Whatever may be the gas, whatever may be the material inside electrons are electrons only. okay say electrons of hydrogen is same as electrons of oxygen which is same as electrons of nitrogen gas which is same as electrons of helium gas okay so all electrons in all the elements in all the atoms is always similar they do have same properties okay so that is what the meaning of the last point so these are the basic characteristics of cathode this and later why do we call them as cathode rays because they emerge from cathode okay they they come from cathode say they called it as cathode rays and later the name was replaced by electrons clear fine and now we will study about charge to mass ratio of an electron guys really very important concept charge to mass ratio uh j j thompson again this was discovered by a person gg thompson he has given a value for charge to mass ratio actually through this value we could able to find out the charge of an electron as well as the individual mass of an electron okay so let us see what experiment he has conducted and how he found the charge to mass ratio of an electron see he took a glass tube the same setup here the glass tube he has taken and he connected uh two two electrodes right he connected one to negative terminal the other one to positive terminal okay you all know that electrons will start coming from cathode side to anode side right so this is our cathode and this is our anode okay and now he made a hole uh you know through this anode he made a hole in the anode so that you can see the anode and you can see the anode and you can see the anode and you can see the the rays can pass through the anode isn't it they will come from cathode and the rays he wanted to get passed out of this instrument so he made a hole here he made a hole here so the rays are coming through the hole okay so when the rays were coming okay so this is one ray one ray of electrons which is coming out through the anode and you know what uh he kept a zinc sulfide scream here he kept a zinc sulfide screen.

So this is our zinc sulfide screen. See guys when you don't have any electric and magnetic field here they do travel in a straight line and definitely they will hit at this point. Let me call this point as A.

Okay say when there was no electric and magnetic field only when those fields are there they get deflected. Their direction gets deviated and they deviate that. towards the positive side of electric field and magnetic field.

Yes or no? Because they are negatively charged. Fine.

So, when you do not have anything, they would travel in a straight line. Fine. And now, I will keep some electric plate.

Okay. And here, it is a positive terminal and this is a negative terminal. Okay. So, I have introduced electric plates, positive terminal, negative terminal.

And now can you all imagine if a ray went travel and come out and where does this ray, how does this ray deviate? How does the direction of this ray changes? Definitely its direction is towards the positive terminal of a plate.

Yes or no? Since the ray is negatively charged, the ray would deviate. It will direct itself towards the positive plate of electric field. Right.

so that's how you will find the deflection uh in the ray in the race direction and it will hit at a point b it will not go straight it doesn't hit that point a now it will hit at point b on a zinc sulfide plate right okay so now let me introduce and now i will take it out i will take out this electric field okay uh i'll take out the electric wind and i'll add a magnetic field Okay, so let me take a magnetic field and this is a south pole and this is a north pole. Consider south pole as positive, north pole as negative. Okay, and now when the ray comes.

When a ray comes, something like this, it is coming and definitely it will show the deflection towards the positive side of the magnet and it will hit on a zinc sulfide plate at a point C. Isn't it? Yes. So when magnetic field is there, definitely the ray would deviate towards the positive side of magnet and it is hitting at point C.

Isn't it? Okay. So now I will introduce both electric field and magnetic field. okay so this is our electric field positive terminal acr and this is our negative terminal of electric field so magnet this is a positive terminal this is a negative terminal now imagine if a ray is passing okay if a ray passing and when it comes at this point can you tell me in which direction will it deviate both electric field magnetic field is there positive terminal of electric field is this side you positive terminal of magnetic field is this side now the negative charge carrying ray is coming so where will it direct here also positive charges are here also positive charges the stronger one okay so the ray will not deviate anywhere the ray definitely will pass straight it will go in a straight line and it will hit at point a it will hit at point a right so when only electric field was there deviation you would observe When only magnetic field was there, deviation you have observed. When both electric and magnetic fields are there in opposite direction, right?

With opposite poles, then definitely the ray will not deviate anywhere. It will go straight and it will hit at point A. See guys, this is the experiment he conducted and based on his observation, based on his observation, Okay, so what did he observe?

What did he observe? Okay, that is based on the amount of deflection the amount of deflection by cathode rays by cathode rays when electric and magnetic fields were kept Okay magnetic fields were kept okay so it must have deviated to certain angle and he calculated the angle of deviation and how much of ray has got deviated to how much extent you know all that he observed and based on that observation he has calculated He has calculated charge by mass ratio of an electron and he got a value as 1.75 into 10 power 11 coulomb per kg. Okay.

So this is the value you have to remember. Charge symbol is E, mass symbol is M. Okay.

So this is charge by mass ratio of an electron. Clear? So you no need to worry about how he got this value.

You will study it in higher classes. So that is not necessary. Just try to understand the experiment and based on the amount of deflection like to which extent the direction of rays are changing and where they are hitting on zinc sulfide screen all that he carefully studied experimentally and by applying lots of mathematics. He calculated this value and he told this value is nothing but the charge to mass ratio of an electron. Okay, so this is really an important value to remember.

Clear? Fine. And now, here one more thing he observed was the deflection.

Okay, the amount of deflection. The amount of deflection was... dependent on was dependent on three factors dependent on three factors guys okay let us discuss what are the three factors on which the deflection you know by looking at the amount of deflection he calculated this value but that amount of deflection the way the direction of race changed was dependent on three factors okay let us see what are those three factors first one amount of deflection amount of deflection was greater was greater when Magnitude of charge was greater.

When magnitude of charge was greater. Okay, that means when the rays were carrying lots of negative charge, then he has observed lots of deflection in the ray, okay, towards the positive side of electric and magnetic field. So greater the magnitude of charge, greater was the deflection.

That is what the meaning of the first point. And coming to the second point, greater the field strength. Greater the field strength or let me write this way.

Greater the strength of electric and magnetic field. Electric and magnetic field. Greater was the deflection.

Greater was the deflection. Okay. So this is another factor. Say the more strength you give, the more deflection you will find in the experiment. Okay, so that is what the meaning of the second point and coming to the third point.

The third point says lighter the mass, lighter the mass of particles, particles, more was the deflection. More was the deflection. Okay, it definitely, logically speaking, this makes a sense, right?

Anything which is lighter in weight will deflect to a larger extent. Since electrons are very lighter in mass, they would have deflected to this much extent, right, when electric and magnetic fields were kept. So, these were the three more observations he has made based on his experiment. So, based on these observations and you know, By applying lots of mathematical applications and knowledge, he arrived at this particular value for charge to mass ratio.

Clear? So this is all about charge to mass ratio. And after that, there is a person called Millikan. So by Millikan's oil drop method, we can find the charge of single electron.

Okay. So charge of an electron was found by Millikan's oil drop method. Once you know the charge of electron, charge by mass ratio of an electron, you can easily find the mass of an electron, right?

So let us see how we can find the mass of an electron. See guys, separate video I will make on Millikan's oil drop method like what experiment he conducted, how he conducted and how he can calculate the charge of single electron and everything. I will do a separate video on that. Now just try to remember charge of an electron. Charge of an electron was found to be this.

I mean it is minus 1.6 into 10 power minus 19 coulombs. So this is the charge of one electron. And this was found by Millikan's oil drop method. okay so don't worry i'll make a separate experiment okay separate video about this particular experiment clear so just remember the value charge of one electron is always minus 1.6 into 10 power minus 19 coulomb okay so now you know charge of an electron charge by mass ratio of an electron you know can't you find out mass of an electron so definitely so uh We all know charge by mass ratio.

Okay, so how much is the value? It is 1.75 into 10 power 11 coulomb per kg. Okay, and we know charge of an electron. So in the numerators value, I know, right?

So what is the charge of an electron? It is this much that is 1.6 into 10 power minus 19 coulomb. Actually, it is minus there is no significance for minus sign here. No need to take a sign just take a value, right?

So divided by mass. is equal to 1.75 into 10 power 11 coulomb per kg right so i want to find out mass here so mass is equal to how do you do 1.6 into 10 power minus 19 coulomb divided by this comes here so 1.75 into 10 power 11 coulomb per kg right so uh this this coulomb coulomb gets cancelled you And on calculating this, you will get mass of electron. So how much is mass of electron? It is 9.1 into 10 power minus 31 kg. Isn't it? So this value is really very important value for calculating any numerical.

Okay. So here three values are important to remember. One is mass of electron. that is 9.1 into 10 power minus 31 kg another important point is charge of an electron is this much found by millikan's oil drop experiment and charge to mass ratio of an electron is this much 1.75 into 10 power 11 coulomb per kg okay so these are the three important values one must remember for calculating any numericals okay so whichever may be the gas whatever may be the electron electron may be there in whatever element okay charge to mass ratio remains common okay so because we all have studied the property of electron doesn't depend on nature of gas or nature of element right so whatever may be the element charge to mass ratio of electron is always this okay fine and charge of an electron mass of an electron.

These are the constant values that you have to remember. So this is all about the discovery of electrons. So we studied how electrons were discovered.

We studied how charge to mass ratio was discovered and we also studied how to get a value for mass of an electron. Okay so with this I will complete this video and in my next video let me talk about discovery of protons and discovery of electrons and also I will come up with few challenging questions that can be asked on this concept. Clear? That's all about today's session.

We will meet up in the next session and do subscribe our channel to learn the concepts in a easiest way and in a detailed way. Thank you so much.

Transcript for:Understanding the Structure of Atoms

Transcript for:
Understanding the Structure of Atoms