Structure of Atom Lecture

for Ruby is this your first class R is this your first class okay is this your first class r no third no your third class no with me it's your first no yeah with you third with my my okay it's my okay I want to know before that I was told earlier that you that you haven't studied the structure of atom yet in you guys didn't studied the structure of atom first yes or no no I think and you were and when I was teaching you periodic I told you about the structure of quantum numbers and why didn't you reminded me then uh I I knew this before so but you didn't now okay there may be chances you know each and everything whatever we are going to teach you but still you need to tell us now and that's why two of your classes got wasted because of I didn't knew I uh I just I I just mixed up two bches two 11 bches so I mix them up that's why the issue came because s already taught structure of item to one of the 11th section but not yes okay s that s that yes sir good evening good evening why didn't you inform me before that you haven't studed structure of ATM yet and I was and I was teaching you periodic properties of element the you should have informed me whatever it is so now we'll start from the basic we are starting from the structure of atom is the screen visible to everyone yes sir okay now we'll be covering everything from the basic okay so the structure of atom deals with the chapter we are studying is atomic structure or structure of atom in here we'll deal about the type structure of atom what initially it has structure of atom we'll start from the history then we'll move to the divisibility which includes fundamental particles that constitute an atom fundamental particles then the properties of them and then there for proton neutron and electron electron are the most important that we going to study further all the properties of the structure of atom around electrons so starting today we are starting with the first thing that's introduction that what are atoms atom are derived from a Greek word which means indivisible the word is Atmos that means indivisible so atoms are particles that are that cannot be further divided into smaller units remember the Greeks have a different view regarding the properties of element according to them atom may be the smallest part but they used to study it in the physics part okay the Greek study science in a much different way than we do today for them atom was a physical property that's why they studied it in the physics why because according to them if it's a block of metal it can if you start dividing it to a number of pieces there will be a point when you can't further divide it and this smallest part since is a physical thing you can see touch and feel it that's why they considered it in physical physics physical property so but over the Advent of time we figured out that atom are much more complicated and are much more smaller than that can be assumed using that can be viewed from a human eye so using this old concept of Greeks there was a scientist in it that came up with a theory known as Dalton's atomic theory he was the first person that came with the theory that there are certain particles that constitute each and everything inside the universe and we call them matters and he gave two laws the law of conservation of mass and law of definite proportion these are your called as basic chemical laws basic chemical laws you may have studied in the chapter number one he later proposed the law of multiple proportion as a logical con quence of this Theory okay D's atomic theory has certain posterior the first one being every element is composed of extremely small indestructible particles that are called as atoms which is similar to the Greek ones but at a much smaller level that the Greeks can achieve then the atom of any one element are similar but they differ from another element for examp example if you got a block of iron a block of iron all the iron atoms will behave same they have same chemical properties same physical properties same type of reactivity there will be no difference like one iron be be acting differently and another different that's not possible the third point the atoms of each Elemental are fundamental particles for fundamental particles we mean that atoms constitute each and everything constitutes each and everything uh any bio person here yeah uh let me see first who it's Amna you who is from bio me okay it's you so remember what I'm teaching you the import uh you are saying something no okay so what's the fundamental particle fundamental particle for a human body the most fundamental thing cell cell similarly for each and everything that exists in this universe the most fundamental particle are atoms that makes up a matter okay so they have a characteristics Mass but they do do not heavy they do not have any structure till date till date we don't know the exact structure of atom till now we are not able to explain what kind of EX structure does an atom have we assume it to be a spherical ball like object although it's still not proven but still this assumption help us to predict various properties of atoms okay now atoms of various elements have different properties hence they combine together in a chemical reaction to form compounds which are often called as molecu any compound the relative number and kinds of atom are constant so for example if you are making a compound of CO2 carbon oxygen to form CO2 there's a fixed number of number of atoms that are required to form a compound for example to form CO2 I always require 1 is to 2 carbon and oxygen in the ratio 1 is to two so that I can obtain the product as CO2 this fifth point is utili is utilized in the law of definite proportion and law of multiple proportion clear clear yes sir okay okay now remember everyone uh this part is specifically for the IIT part okay it's not important for the need section they have remove omitted this part so it's not necessary for you to read but for Education purpose you should learn okay it's not for your exam purposes and remember uh no questions come from this part it's just for your understanding okay so first we have the cathode race which is which resulted in the discovery of electron so in the year 1837 I guess oh sorry 1819 there was scientist called Kook c r o o k krook he constructed an experiment in which he was studying the flow of current he was studying the flow of current so he he took a perforated glass tube perforated means empty but filled with a gas perforated glass tube which made of quartz it contains a gas H2 at a low pressure at low pressure and he put two electrodes in the tube one the cathode and other is anode every everybody know about cathode and anode yes yes sir okay so he he took two electrodes put it inside the tube and connected it with two ends of a high powered battery okay he filled the gas inside the tube at a low pressure of around 10 to 10 to 2 mm HG okay and then he passed electric current through it so what happened when you pass a large amount of electric current such as th000 volt which is nothing but potential which is nothing but potential which is ability to move a charge to move a charge from one point to another so what happens is when you apply such high amount of voltage the molecule the hh2 molecule that has electron in them remember initially this was not known how com elements combined together to form compounds was initially not but what happened is when you applied large amount of potential this gas become charged because of the flow of current from the electricity this gas becomes starts and wait let me Zoom it and then he observed a green glow around both of the he observed a greenish light at the anode and a bright light near ano okay but this gas but this light was only confined to this electrod you cannot see beyond it there was dark space between them means there was no light this was called as K's dark space under this condition the electric current started to flow from one electrode to the second electrode okay because since the circuit was complete the charge was flowing the electricity can be measured if you put up an emiter here okay so the cathode surface started glowing and the cathode space left between the CL and the cathode was named as kou's dark space which is after the scientist so when the pressure is sufficiently low we further press down the two 10 to the power minus1 to 10^ -2 mmhg so what happened is in this tube when you are increasing the pressure when you are pushing the gases inside very close to each other the gases comes very close Okay since they are very close and each of the gas particles are made of electrons are made of electrons the charge they acquire the charge density would be very high the charge density would be very high and what I mean by charge density is that number of charges per unit area per unit area so since in a smaller space when you put a pressure it's just like when you uh put weight on the suitcase to push uh so that you can pack more clothes so when you push the charge gets very close to each other by increasing the pressure and when we further pass down the electricity to it it was done by JJ Thompson in 1897 using the same method and the gas at very low pressure he noticed that the emission of visible rays which produced flosin on the glass and influen photographic plate these rays were called as cathode race okay everybody understood till the crew part I'm going to explain the thumbon part everybody understood the Kooks part I'll further explain it's either a yes or a no um could you explain when the pressure is sufficiently low okay let me go little down have a clear picture Okay suppose this is a beaker okay and there's a gas that can free flow it now I have closed this Beaker and now I started pushing this block whatever it is to the down when I start applying the pressure the gases suppose the block is somewhere here now the gas that was flowing in this Total Space is now confined only to this finite space so when I further add pressure which is very low the gas is confined in a very small place the particles come very close Okay since the particles are very close and each fundamental particles are made up of electrons so each hydrogen gas has electrons so when we pass the electricity to it the electrons this hydrogen due to the potential these electrons get trans gets moved or this hydrogen molecules acquires a charge because of this high pressure remember usually all the gases are non conductors that each each and everyone knows gases are non-conductors yeah okay at normal temperature and pressure gases are nonconductor why because between each gas molecule there's a very large difference so in charge cannot be transferred to such a large distance so what we do is when we increase the pressure it means we are trying to bring the molecules very close by decreas remember 10^ minus 2 means I have removed the excess of gas which can interfere okay so the particles are very close to each other so now since they are very close to each other this hydrogen molecule can easily transfer his charge to a nearby molecule so this increases the conductivity for a gas that's why they can trans for charge so when R for did this experiment he further reduced the pressure which okay and now let me remove this part but what RF for did is raford made some holes in this ano and then he covered the backside of anode with a floresent material Flor and materials are those material that emit light when they do not receive any source for example like in your childhood you would have uh radium watches that when you uh let them when you let them in the sunlight for some time they glue in the dark those are fluorescent materials that absorb the light and that later emitted floresent material like zns zinc sulfide so since the pressure is very low and he discharg charge the electricity to it the entire gas starts glowing the entire tube starts glowing not just near the cathode but the entire tube and then he figured out the places where he had made holes there are C made holes okay here he observed some marks exactly at the places where he had made the holes these shiny okay these shiny bright spots shiny bright spots were exactly at the places where he had made the holes in the anod okay then he come up with this idea that since the rays are coming from the cathode and and ending up at the anode and anodes are positively charged by Nature so this means that the particles that hit the anode were possib negatively charged since the particles pass through this holes and hit exactly at the spot where the zinc sulfide was covered in a straight line this means the particles also travels in a straight line clear yes sir okay so the cathode rays consist of negatively charged particle known as electrons why because cathode rays traveled from cathode to anode since anode are positively charged so only negative particles get attracted to the anode that's why we call them negative charge or called as electrons okay cathode rays travel in a straight line because we got the marks exactly at the point where we have made holes in the anode with the speed order of 10 to the^ ra 7 m per second and they produce Shadows of the object play in the path okay what does this means this means okay you each one of us have Shadow because we are material particles we are material particles light cannot pass through us that's why we get Shadow so if cathode race makes shadow of an object this means they are also material particles material particles that means they can be blocked by a human being or an object so that a shadow is C clear yes everybody clear or doubts so that I understood sir 100% sure yes okay if any doubt uh someone is hesitant to ask me directly please answer in the public uh private chart now cathode rays can pass through thin layers of metal since they can pass through thin layers of metal which means they are very small in size very small in sides cathode rays are emitted from the S surface of the cathode and their direction is not affected by the position of the anode so no matter matter what if you are placing an anode here and the cathode is here or if the anode is here they'll always travel in a straight line no matter what clear because because and this can be confirmed using a zinc sulfide R so cathode rays have high kinetic energy kinetic because everything that moves have kinetic energy in them so cathode rays are moving particles that's why they have high ktic energy why because kinetic energy is given by half M v² and they have large velocity of the order 10 the^ 7 m/ second so they have large kinetic energy they exert mechanical pressure on an object for example if in the tube you place a mechanical fan here of metal or plastic whatever you do if you start the experiment you see this fan starts moving in the direction it will start moving from one to other and starts rotating this means that these particles are hitting the fan that's why they are moving and this is also a property of a material particle just like you hit a fan and it start moving okay they can produce heat when stopped by matter if they are flowing free flowing from one thing to another there's no issue but if something blocks them they transfer all of its kinetic energy to this object in the form of heat which leads to the heating of the object this we see in our microwaves our microwaves heat the food using this principle okay they can ionize any gas since this gas is all since they are already in the ionic form because of the high potential if they encounter any neutral molecule they will also ionize it they will also ionize it clear wa that share Char what uh how do the ion ionize the neutral okay how do the see okay how do the okay see this is the cathode and the gas that lying the gaseous molecule that lying closest to the cathode will receive the electric current first from this wire clear yeah okay and now there are tons of sorry there are hundreds of thousands of molecules of gas inside it okay so since they are closest to the cathode will get charged first because they are in directly contact with this cathode yeah since and now the charge transfer from this atom to this to this to this that's why the entire tube starts glowing okay if the charge is not transferred will still obtain a glow just near just like krooks obtain okay but Thompson prove that these G these molecules get charged and travel and charge anything that comes into their path so that's why the entire tube starts shining because of the large current because all of these particles are charged by these particle that lie near this to the cathode so basically they all share the electron right yeah they all sh they all have their electrons they don't share electrons the electrons are coming from that it's just transferring from one part to it's like jumping from one place to another oh okay okay okay now cathode rays are deflected since they are material particle they can be deflected just like you throw a ball to a wall it gets deflected back by electric and magnetic field cathod R can be deflected by electric and magnetic field because cathod Ras are made of electrons electron are charged particles and both electric and magnetic fields are also made up by charged particles and charge particles if they are having same charge or opposite charge this particle will either get attracted or gets deflected in both either of the cases the path of this electron would be changed so that's why they are deflected in electric and magnetic field clear yeah okay the cathode race produce fluocin fluocin as I explained is the ability to emit light even after the source is removed when they fall on certain substances like zns the color of the fluoresence varies with the chemical nature of the substance for example if you take a highly conducting gas other than hydrogen the amount of fluocin that will you that you'll absorb would be more the the the perforated tube will shine more brightly the cathode rays can produce a chemical change and thus they affect a photographic plate photographic plate just in your if you have seen in the older time we've got photographic camera reels anybody seeing photographic camera reels anyone I have seen s be brown sheet of paper with some imprint on it oh yeah the brown sheet of paper the brown sheet of paper has a quoting of AGI on it silver iodite when it is exposed to Sun Sun contains the sun rise also contains electrons okay we commonly call them as photons in the form so the cathode R they hit the photographic film surface and it affects the color because the compound gets broken down into its ini to its ionized form leading to the different colors that you obtain for a photograph so cathode R produces chemical change because it can either decompose a compound or can allow a chemical reaction to occur that's why the effect of photographic plate the cathode race also Al produces xrays when they strike a metal surface of very high atomic number just like tungster this you have seen in your suria bu everybody have seen suria bulbs the one with this St rounded wire the yellow bus yeah so we have seen this type of in spon which are highly penetrating but remember the tone that we use in our homes is far is far less it is a combination of different Metals so it do not affect us much but when you go for an x-ray we use pure tone that releases x-ray that has the power to pen penetrate to our skins highly penetrating so JJ Thompson determine the EM value which is charge to mass ratio of an electron okay by studying the deflection of the cathode rays in electric and magnetic field he figured out the value of charge by mass is 17588 to 10 the power G8 Kum per G clear here I'll explain what's charge to mation why we need it yeah what I was going to ask that no I was I'm going to explain I know I know you guys don't know this thing so I have to teach you okay so what does charge to mass ratio means so initially listen charge to mass ratio means how much charge you are giving for example this is the tube there's the cathode there's the anode how much of since you are taking a gas you are taking a gas of gas has certain volume has certain volume this means it has certain Mass so the amount of gas that you are taking how much charge does it produce okay how much charge does it produce that can be figured out by using charge by mass ratio since the electron is just being discovered we don't actually know the mass of the electron and we don't know the charge of the electron these both things are unknown to us but we do know the amount of gas that we are taking here clear clear clear yes okay so what JJ Thompson did he took out he took some amount of gas and recorded the Char that this gas producing so and when he he figured out that for each one g of gas that he has taken the amount of charge that he's getting equivalent to this Val clear for each 1 G of gas the amount of charge that we are getting is this that's why we are using charge by mass ratio because we don't know the actual mass of the Elon and the actual charge of the electron we are we have just discovered the particle but so the only thing that I control that the amount of gas that I am taking and the charge that I can get from this whole experiment these two things I can measure clear clear why we are using charge by mass ratio because it helps us to Quant how much amount of gas do I take to receive this much of charge how much current do I need to prod how much current it produces clear oh yeah okay so by charge by mass ratio JJ Thompson was able to explain that how much gram of gas you need to require to get a charge but he still didn't answer the mass of an electron the charge of electron since it's a material particle it should definitely have a mass so here we got micans oil Rock experiment the theory of this experiment is not in your cabus not in cabus we don't need to read it we just only need the conclusions so Mican soil drop experiment was the first helped in the first precise measurement of the charge of an electron this helped in the knowing the charge of the electron which is made by Robert a Milik the charge of the electron was found to be minus 1.6 please make sure you remember this value 1.6 10 ^ - 19 Kum an electron has the smallest charge known so it was designated as a unit negative charge because they originate from the cathode cathodes are negatively charged hence they are considered as negatively charged particle so after the O dment experiment we knew the charge by mass value we knew the cym ratio and now I know the charge of the electron so this using this formula I can directly figure out what is the mass of an electron so the charge of an the mass of electron given by the charge that it has one electron divided by the E by m charge by mass ratio do you guys have studied Dimensions physics okay so let me open up this formula for you so mass of electron divided by charge of an electron divided by E by m value so if I open this e divided by multip by m can you see the dimensions the dimensions of a mass are left yeah okay so when I divide the charge that it has carry and the charge each gram of gas that we have when we solved it we figured out that the mass of the electron is 9.1 10^ - 28 G or since SI unit is kg we converted it to this 9.1 * 10^ - 31 kg okay now I'm taking two minutes so that if anyone has a doubt please ask me or something else regarding me like am I going too fast uh my voice is my speech is not clear anything like this or if you have a doubt am I that good answer please the public chat yeah yes good I don't have any okay so and R yes sir s that I have a lot of Doubt regarding you I'm not sure if you are if you know okay okay this is called this 9.1 is called as the rest mass of an electron rest mass of electron when the electron is is not moving the mass of electron when it is moving with a low speed we can calculate using this formula okay this is called reduced Mass Al there are other formulas for it too where the m not equals to the mass of the electron when it is at rest when the velocity B is the velocity of electron C is the velocity of light and M is the relativistic relativistic means relatively we are checking it with respect to the speed of light clear so remember when an object travels with a higher speed its mass gets considerably low when an object is dy is moving at a faster speed the ma its mass gets decreased clear if you have seen drag racers or F1 cars you have seen those cars sometimes gets pulled upward when they are driving at a very high speed because of this this is given by Theory of Relativity by was Albert Einstein okay when you apply this formula we see if the object starts traveling at a higher speed okay its mass will get decreased since mass is inversely proportional to velocity velocity of the object since C which is speed of light is constant it do not change so it will not have any effect on the mass of an object okay so if the velocity decrease okay when Mass decreases the velocity increases and when you try to put up a molecule very fast like if you reach it to a velocity of infinity the value of M1 by B becomes nearly zero this means at this point the mass of electron cannot be found clear the results are not that important we only need to remember this part and this formula please clear yeah okay so an electron is defined as a subatomic particle carrying a negative charge of this value one unit negative charge and has the mass this into if it's not okay that's wrong it should be 10 the^ minus 28 okay and this mass is equals to 1 by 8837 time the mass of the hydrogen atom which is 0.549 a okay now we are moving forward to discovery of protons the positive race it was done by Goldstein what it did it did the same experiment that JJ Thompson did but instead of making holes at the anode this time he made holes in the anode oh sorry in the cathode he made holes in the cathode and covered the side of the cathode with the source and material like zns he took up a gas it put up several thousand volts of current and he realized and he observed the same thing that he observed with the cathod r they also travel with straight line but they originated from the anode they travel from anode to the cathode and leave the same marks just like the cathode race since they originated from the positive side they are termed as positive Rays Canal Rays or sometime also as anode Rays the same experiments just the opposite thing okay okay again we came across the same thing specific charge by mass ratio for Canal R varied with the nature of gas what be figured out that the charge by m value for Canal race changes every time you switch to a different gas for different gases like H2 helium helium uh oxygen nitrogen for this the electrons the cathode charge by mass ratio value do not change for the cathode ray charge by mass value do not change it remains same for each and every gas but for the C anode Rays the C by m value changes every time you change the gas changes with the gas every time you change the gas so the nature of the gas and was found to be maximum for the H2 why maximum because e by M the mass is since hydrogen is the first element since it has the lowest Mass so the lowest denominator makes the largest fraction that's why it says the maximum charge by mass Val the positive rais particle then thus called as positive charge gaseous atoms that are left after the removal of electrons or ionized gas atoms for example so in the tube we in the tube we got anode rays which are positively charged and how this will be produced like for example if you have the H2 gas this high potential stripped the electrons of the hydrogen molecules converting it to either this form or maybe decomposing the gas clear the high potential that you applied manage to strip of electrons from this hydrogen molecules or may it may have decomposed the gas to its Elemental form to release the electrons that hit the anode on this side clear clear okay however if H2 gas is used in the discharge the positive Rays particles are named as protons since we have used hydrogen gas which is the lightest has the highest charge by mass value we call the these partic positively charge particles as protons which is called as P so the atomic particle that constitutes all matter is called as proton it has mass 1.6 10^ - 27 and charge equivalent to electron clear so which of the following is heavy which of the following is a heavier particle which of the following is a heavier particle proton proton why the numbers numbers s and RI is it clear to you why proton is heavier can you repeat again which of the following is the heavier particle mass of electron and mass of proton which of the following is what sir heavier okay sir it is the mass of proton I believe uh the mass of proton it's heav because the negative power means it's in fraction so the larger the denominator smaller the fraction that's why okay summary what we have written now the charge by mass ratio for the proton is given this mass of one mole of proton one mole of proton means 6.022 the power 23 proton atoms so mass of one proton multiply the Avogadro number Na and we get the mass 1.76 10^ minus 3 in form of kg the radius of proton which is your nucleus is 1.53 10^-3 CM also sometime written as 1.5 1.5 F FM and 1 FM for = 10^ -5 meter clear it's your s it's your unit of measurement for 1 feter = 10 ^ - 15 M and the radius of proton usually lies in the range of 1.2 to 1.5 FM FM the volume of proton since we are assuming that it is a sphere the volume is given by 4x3 pi r CU and on solving the putting the value of R we got the answer 1501 ^ minus 38 the charge on the positive Rays is usually one but it may be +2 and + three depending on the type of gas that you are using okay in older time times the television picture if you have seen the big televisions they have a fluorescent light tubes that are called as Cod tubes okay those tubes are used to produce the image on the TV in the older times using the fluos the light tubes called as cathod tubes that's how okay now further okay this is the part for both neat and I earlier model of atom the first model of atom we have is Thompson okay based on Thompson Thompson did found the particle called electron Goldstein found about the proton and Thompson found electron Goldstein found proton so and when they both concluded the experiment the charge of electron the charge of electron was nearly to the equal to the charge of proton since they both are part of an atom JJ Thompson come to the conclusion that the nucleus is made up of both proton and electron JJ Thompson concluded that and at okay when we figured out the fundamental image of the particles constituting an atom everybody started fighting what what would be the structure of atom since dton said the atom do not have a fixed structure okay so JJ Thompson used the criteria for the charge of proton equals to the charge of electron to derive to devise his model of atom so after the discovery of proton and electron Thompson proposed a watermelon like model in which the atom is considered as a sphere with net POS positive charge spread across the watermelon like the red part with the electrons distributed just like we have the seeds of the watermelon okay within the square of radius 10 the power minus 10 m to give the most stable electrostatic agreement okay this model is also be represented as a pudding or a cake with a positive charge with raising electrons embedded in it a major point of this model is that the mass of an atom is considered to be spread uniformly across the atom the plus that you are seeing is are the protons and the electrons are embedded in it okay what does we mean the most agree most stable electrostatic agreement we mean that the charge of elect neon is nearly equals to the charge of proton Thomson said the atoms are neutral particles neutral particles this single line was the reason today we are studying about Thompson Thompson's model of atom although this model has various flaws but this single thing that tells about the neutrality of mod the electr neutrality of an atom made was an important thing that we needed to consider that's why we are studying Thomson's model of atom today but okay what are the issues with Thomson model of atom the Thompson's model of atom fail to explain how positive and negative charge electrons are arranged how they are arranged it cannot be randomly filled it also feel to explain the atom stability for example if positive and negative charge are staying this close to each other there should be a exchange of energy in between them but we know that atoms are stable particle because if they are continuously sharing the energy in between them we would have been experiencing some kind of phenomena throughout our life but in our life we see we don't see such kind of phenomenas okay the theory did not mention anything about the nucleus of item it do not told about the arrangement of proton how they are arranged how their electrons are arranged what is the how different elements have different proton Arrangement or not and it was unable to explain the scattering by the RF experiment okay remember JJ Thompson found electron Goldstein found proton and Chadwick found NE can you scroll up slightly sir okay yes sir continue yes okay so JJ Thompson found electron Goldstein found proton and ched found Neutron okay so JJ Thompson's student was Goldstein and Goldstein students were shed all of them got Nobel Prize both student and teacher now what did RF for did ra for conducted an experiment okay Le for conducted a series of in experiment using alpha particles alpha particles are your doubly charged helium atoms sorry helium ions W charged helium ions are called as alpha particles commonly shown as h2+ they are your alpha particle a beam of alpha particle is directed against a thin tin foil of gold platinum silver or Co the foil was surrounded by circular fluent zinc screen like znl whenever an alpha particle stricks the screen it produces a flash of light okay this is the experiment setle uh setup he used okay this is a radioactive element radioactive element and it is the source of alpha particle it produces a alpha particle species so what Goldstein did he took up a gold foil this is the gold foil he put it bited in a very thin fine sheet and this is the collyer also called as col meter collyers is a substance that help us to direct turn the beam into a single fine line so the source has producing alpha particle that are are going in different direction but some particles passes through the small Screen through the Coler and hits the gold fil so around this gold fil there are number of fosen materials and these part these alpha particle found to scatter in different directions okay the transmitted Beam with no deflection that came goes straight to to the sheet a there are some that deflected to sheet B and there are some that deflected towards the sheet C so during this experiment LEF figured out that most of the alpha particle passed straight through the foil without any deflection that means most of the alpha particle were hitting the Cent relation sheet a and some of them were deflected by a small angle small angles like this this is a small angle hitting b and a very small number of which is one particle in every 20,000 particle did not pass through the field but suffered a rebound which is a 180° deflection which means this particle went straight hit up the gold foil and went back to the source okay so what are the conclusion that we can draw from this experiment since most of the particles for hitting the sheet a we figured out that most of the space around an atom would be empty why helium particles are positively charged so this means if there is a positively charged Center somewhere in an atom where the proton lies and they are positively charged only proton will deflect this positive charge because positive charge refs the positive charge so most of the particle positive particle State went from the Alpha from the gold shield proving that most of the space inside the atom was empty that's why they pass straight now some of the particles were deflected through their original part through moderate angle like okay like from this picture we see majority of the particle that hit the sheet a pass straight through the atom and the particle that suffered deflection they hit they were near the positive charge space where the proton was lying and that's why they are deflected from their Direction and the particle that directly hit the POS in the line of the direction of the proton was sent by 180° back okay clear everyone clear can you scroll up okay okay so now okay considering this Rond came to a conclusion that most of the space around the nucleus is empty okay and he came up with the formula R is = to R A to the power is 1X 3 where this a is mass of an element mass of an element that you are taking okay you figur out and the r not he found was .52 angrong one angrong means 10 to the power - 10 m okay so you figur out okay this R not is the radius of suppose this is your first shell this R not is the distance between the nucleus and the first orbit and the first orbit which is 0.52 angrong clear if you see the nucleus was having a 1.2 fir me distance which is around 10^ -5 M but the radius to the first orbit is 10 the power 10 m which is a difference of 1 lakh times so this means if there is a nucleus the first orbit is around 10 L times further from the nucleus clear this further proves that the distance around the nucleus is empty clear clear oh yeah okay can does anybody like to take a guess how much one L distance means around if I would like to explain it in a real life can you assume the what does one lak times means how farther it would be I think almost towards USA almost almost goes to USA it's like you are sitting somewhere in South India let's for example let's go for kyak you sitting in Kumari and I'm mas and the distance to the first orbit is is more than the North Pole is more further than the North Pole clear the first orbit Li this part that's why most of the alpha particle pass straight through the nucleus okay explain briefly how other Force scattering is a particle by Target nucleus provide information on the size of nucleus okay considering the nucleus as a sphere it will have a some kind of volume the mass of the nucleus would be m whatever since there is a nucleus it would have protons so whatever the mass of the proton have or if the electrons are lying inside of it the total mass would be M and the radius of the nucleus are since this is the if this is the nucleus the distance would be R so the total distance for R not is given by 1.2 for me to 1.5 which is the r radius of the nucleus since if it's a hydrogen atom the nucleus would be small and during the uh anod experiment we found that number that the posit sorry that the anode Ray values anod Ray charge by m value varies as you change the gas so for a heavier atom the charge by mass r value would be lower it will be lower now so the radius of the nucleus will also vary with the mass because there will be different number of protons and electron that would be residing inside this nucleus we are still considering JJ Thompson's theory that proton and electrons are lying inside of each other okay now J rather for discarded this thing why since if proton and electron would be existing coexisting inside the nucleus the alpha particle that is coming towards the nucleus the electron should be able to hold it the alpha particle should be attracted towards the nucleus but it was repelled by it that means the electron and proton cannot lie in very close to each other so that means the electron must lie outside the nucleus the electron lie outside the nucleus and the nucleus mass and the radius of the nucleus would vary according to the change in mass given by the formula R is = R A1 by 3 where a is the mass number so density is of a nucleus is given by mass by volume mass is the mass of a single proton multiply total number of protons divided by volume 4x3 p r Cub putting the value of r as R A1 by 3 RQ would be equals to r q multip with a can you repeat again sir okay let me remove it first okay now I need to find the density of a nucleus okay so density is given by mass by volume Vol mass of a nucleus is given by how many number of proton does it have and the mass of one proton this would be the mass of the nucleus now okay and the volume is 4x3 piun R Cub 4x3 < R but we know r = r a^ 1 by 3 yes sir so R would be r 1 3 3 yeah yes just how do we get that r = r a 1x3 okay r = r 1x3 is derived by brother for this is the formula that you need to remember we are not deriving this formula this formula was by okay okay okay so for this three removes three and we got 4 by3 pi r q a a cancels a this three goes above and we I got DS 3 m which is the mass of one proton sorry and 4x3 Pi are not Q so if you clearly see the density of this nucleus do not contain any Mass terms for a nucleus this is the mass of the nucleus it do not contain the mass of the nucleus the atom it only contains the mass of single proton clear yes everybody clear yes sir okay so since this is many this is missing this a value is missing this proves that the density of a nucleus is independent of inde dependent of mass of a nucleus so if you have a iodine atom which has atomic mass 107 and if you have a hydrogen atom which has mass one they both will have same density they will both have same density irrespective of the atom they have so this proves that the density of a nucleus is independent of its mass number a the volume of nucleus is directly proportional to the number of nucleons constituting the nucleus but how many number of proton does it have but the density won't change the density won't change means what okay density is mass by volume suppose this is a nucleus since protons are adding with increase in atomic number the mass is increasing clear everybody clear so the density should also increase but when the number of protons start increasing in the nucleus the nucleus also increases its volume to accommodate this much number of proton inside because these proton also repel each other they also repel this repulsion increases the size of the nucleus which in turn increases the volume okay so the mass increases and at the same time the volume is also increasing so the density that is increasing by the increase in mass is cancelled by the increase in volume clear that's why the density of the nucleus do not change remember the density of a nucleus is constant everybody clear please answer me or at least please reply in chat when I ask please yeah it what about the rest two yes yes sir you sure you guys don't have any doubt okay okay now the where I was I was discuss okay the discovery of neutron by Reser for model of atom so when RES for was doing his experiment there are also some particles that were emitted by the react further it he further combined this experiment with different elements so while doing Chad okay there was James Chadwick that bombarded berium with the stream of alpha particle and he observed that the penetrations were not affected by electric and magnetic field that during this the Barum there are particles that are helium particles that are hitting the berum atom so there there should be the certain uh there should be signs like Sparks that we have seen on zinc that we also saw in Beria but we only saw particles in a straight line let me show you what happened is he constructed a this was a tube there was a source that striking alpha particle and there was a berum when alpha particle strike there were two magnets nor Pole and South Pole these particles hit if okay when the particles if there were electrons they would be deflected by there would be an no R deflected by another magnetic field if they were protons they were again deflected by electric and magnetic field but the particles that hit the this zns surface were hitting in the straight line they weren't affected by this presence of magnetic field that these magnets were applied so Chadwick came to a conclusion that there are also apart from electron and proton there is also a particle which is neutral which do not have any charge also constitute a nucleus since it by do not have a charge because if it had charge it should be deflected by electric and magnetic field this is the reaction and he called these particles as neutrons which means neutral particles the mass of neutron is given by 1.6 10^ - 24 kg okay the proton wait the proton okay the proton have nearly mass of neutron so that is nearly equal to the mass of the proton th a neutron is a particle having Mass this approximately 1 AM U or nearly equal to the mass of proton or hydrogen atom whenever I say hydrogen atom I'm considering both one proton and one electron and when I say proton only I can also write proton as H+ which means it only contains one proton zero electron okay and it carries no electrical charge so it has the charge to m ratio as zero clear yes okay now I'm ending the class here today if anyone has a doubt please ask I don't have any doubt and uh this topic is very boring last class were most more fun last class what was more fun it is Theory yeah it'll take some time to build up a chapter I'll also I also have some questions regarding this that I know for sure you guys won't be able to solve even if I show you show you the solution to it but it's it will take some time for this chapter to build and look what I'm telling you the whatever part we have read today is just the History part remember nothing will come in your exam from this part nothing except except except for this one part which may have a potential chance uh where is where is is where it is where it is where it is where it is uh this one formula and apart from this this that raford Pro that the D it of an of a nucleus is independent of the atomic mass of a substance okay these are the only two points like I said the chapter is currently building the important question that that you can receive in your exam will come from the quantum mechanics part uh quantum mechanics I have tons of questions okay so don't worry it'll be fun but I need to cover the History part first because I can't something I had to give an intro so we have a class tomorrow I'll make sure I'll have some good things for you and some questions too we are starting with the model of item once finished we'll go for the quantum part and discussing the items and all once the theory part is done we'll purely focus on questions okay what's your thought I have no doubts no one has doubt it was just Theory like I said it's not that complicated you have studied in class 9 and 10 the model of items still the same thing nothing much the only thing you need to remember from today the density of the atom is independent of atomic mass the only thing you should remember about it for the past course of years the questions from this part have reduced even after 1990s there is no such question regarding the that I have that they have asked from this topic after 1990s there is no question literally after I guess 1998 there's no question from this topic till now because it's Theory complete Theory it do not since it's history and it's no longer used so they focus mainly at questions from the quantum Parts because that is currently used and we are currently exporing the prospective of quantum so should I end the class if no one has a doubt just answer yes in the chat and I'll add it yes sir okay thank you e e e e e e e e e

for Ruby is this your first class R is this your first class okay is this your first class r no third no your third class no with me it&#39;s your first no yeah with you third with my my okay it&#39;s my okay I want to know before that I was told earlier that you that you haven&#39;t studied the structure of atom yet in you guys didn&#39;t studied the structure of atom first yes or no no I think and you were and when I was teaching you periodic I told you about the structure of quantum numbers and why didn&#39;t you reminded me then uh I I knew this before so but you didn&#39;t now okay there may be chances you know each and everything whatever we are going to teach you but still you need to tell us now and that&#39;s why two of your classes got wasted because of I didn&#39;t knew I uh I just I I just mixed up two bches two 11 bches so I mix them up that&#39;s why the issue came because s already taught structure of item to one of the 11th section but not yes okay s that s that yes sir good evening good evening why didn&#39;t you inform me before that you haven&#39;t studed structure of ATM yet and I was and I was teaching you periodic properties of element the you should have informed me whatever it is so now we&#39;ll start from the basic we are starting from the structure of atom is the screen visible to everyone yes sir okay now we&#39;ll be covering everything from the basic okay so the structure of atom deals with the chapter we are studying is atomic structure or structure of atom in here we&#39;ll deal about the type structure of atom what initially it has structure of atom we&#39;ll start from the history then we&#39;ll move to the divisibility which includes fundamental particles that constitute an atom fundamental particles then the properties of them and then there for proton neutron and electron electron are the most important that we going to study further all the properties of the structure of atom around electrons so starting today we are starting with the first thing that&#39;s introduction that what are atoms atom are derived from a Greek word which means indivisible the word is Atmos that means indivisible so atoms are particles that are that cannot be further divided into smaller units remember the Greeks have a different view regarding the properties of element according to them atom may be the smallest part but they used to study it in the physics part okay the Greek study science in a much different way than we do today for them atom was a physical property that&#39;s why they studied it in the physics why because according to them if it&#39;s a block of metal it can if you start dividing it to a number of pieces there will be a point when you can&#39;t further divide it and this smallest part since is a physical thing you can see touch and feel it that&#39;s why they considered it in physical physics physical property so but over the Advent of time we figured out that atom are much more complicated and are much more smaller than that can be assumed using that can be viewed from a human eye so using this old concept of Greeks there was a scientist in it that came up with a theory known as Dalton&#39;s atomic theory he was the first person that came with the theory that there are certain particles that constitute each and everything inside the universe and we call them matters and he gave two laws the law of conservation of mass and law of definite proportion these are your called as basic chemical laws basic chemical laws you may have studied in the chapter number one he later proposed the law of multiple proportion as a logical con quence of this Theory okay D&#39;s atomic theory has certain posterior the first one being every element is composed of extremely small indestructible particles that are called as atoms which is similar to the Greek ones but at a much smaller level that the Greeks can achieve then the atom of any one element are similar but they differ from another element for examp example if you got a block of iron a block of iron all the iron atoms will behave same they have same chemical properties same physical properties same type of reactivity there will be no difference like one iron be be acting differently and another different that&#39;s not possible the third point the atoms of each Elemental are fundamental particles for fundamental particles we mean that atoms constitute each and everything constitutes each and everything uh any bio person here yeah uh let me see first who it&#39;s Amna you who is from bio me okay it&#39;s you so remember what I&#39;m teaching you the import uh you are saying something no okay so what&#39;s the fundamental particle fundamental particle for a human body the most fundamental thing cell cell similarly for each and everything that exists in this universe the most fundamental particle are atoms that makes up a matter okay so they have a characteristics Mass but they do do not heavy they do not have any structure till date till date we don&#39;t know the exact structure of atom till now we are not able to explain what kind of EX structure does an atom have we assume it to be a spherical ball like object although it&#39;s still not proven but still this assumption help us to predict various properties of atoms okay now atoms of various elements have different properties hence they combine together in a chemical reaction to form compounds which are often called as molecu any compound the relative number and kinds of atom are constant so for example if you are making a compound of CO2 carbon oxygen to form CO2 there&#39;s a fixed number of number of atoms that are required to form a compound for example to form CO2 I always require 1 is to 2 carbon and oxygen in the ratio 1 is to two so that I can obtain the product as CO2 this fifth point is utili is utilized in the law of definite proportion and law of multiple proportion clear clear yes sir okay okay now remember everyone uh this part is specifically for the IIT part okay it&#39;s not important for the need section they have remove omitted this part so it&#39;s not necessary for you to read but for Education purpose you should learn okay it&#39;s not for your exam purposes and remember uh no questions come from this part it&#39;s just for your understanding okay so first we have the cathode race which is which resulted in the discovery of electron so in the year 1837 I guess oh sorry 1819 there was scientist called Kook c r o o k krook he constructed an experiment in which he was studying the flow of current he was studying the flow of current so he he took a perforated glass tube perforated means empty but filled with a gas perforated glass tube which made of quartz it contains a gas H2 at a low pressure at low pressure and he put two electrodes in the tube one the cathode and other is anode every everybody know about cathode and anode yes yes sir okay so he he took two electrodes put it inside the tube and connected it with two ends of a high powered battery okay he filled the gas inside the tube at a low pressure of around 10 to 10 to 2 mm HG okay and then he passed electric current through it so what happened when you pass a large amount of electric current such as th000 volt which is nothing but potential which is nothing but potential which is ability to move a charge to move a charge from one point to another so what happens is when you apply such high amount of voltage the molecule the hh2 molecule that has electron in them remember initially this was not known how com elements combined together to form compounds was initially not but what happened is when you applied large amount of potential this gas become charged because of the flow of current from the electricity this gas becomes starts and wait let me Zoom it and then he observed a green glow around both of the he observed a greenish light at the anode and a bright light near ano okay but this gas but this light was only confined to this electrod you cannot see beyond it there was dark space between them means there was no light this was called as K&#39;s dark space under this condition the electric current started to flow from one electrode to the second electrode okay because since the circuit was complete the charge was flowing the electricity can be measured if you put up an emiter here okay so the cathode surface started glowing and the cathode space left between the CL and the cathode was named as kou&#39;s dark space which is after the scientist so when the pressure is sufficiently low we further press down the two 10 to the power minus1 to 10^ -2 mmhg so what happened is in this tube when you are increasing the pressure when you are pushing the gases inside very close to each other the gases comes very close Okay since they are very close and each of the gas particles are made of electrons are made of electrons the charge they acquire the charge density would be very high the charge density would be very high and what I mean by charge density is that number of charges per unit area per unit area so since in a smaller space when you put a pressure it&#39;s just like when you uh put weight on the suitcase to push uh so that you can pack more clothes so when you push the charge gets very close to each other by increasing the pressure and when we further pass down the electricity to it it was done by JJ Thompson in 1897 using the same method and the gas at very low pressure he noticed that the emission of visible rays which produced flosin on the glass and influen photographic plate these rays were called as cathode race okay everybody understood till the crew part I&#39;m going to explain the thumbon part everybody understood the Kooks part I&#39;ll further explain it&#39;s either a yes or a no um could you explain when the pressure is sufficiently low okay let me go little down have a clear picture Okay suppose this is a beaker okay and there&#39;s a gas that can free flow it now I have closed this Beaker and now I started pushing this block whatever it is to the down when I start applying the pressure the gases suppose the block is somewhere here now the gas that was flowing in this Total Space is now confined only to this finite space so when I further add pressure which is very low the gas is confined in a very small place the particles come very close Okay since the particles are very close and each fundamental particles are made up of electrons so each hydrogen gas has electrons so when we pass the electricity to it the electrons this hydrogen due to the potential these electrons get trans gets moved or this hydrogen molecules acquires a charge because of this high pressure remember usually all the gases are non conductors that each each and everyone knows gases are non-conductors yeah okay at normal temperature and pressure gases are nonconductor why because between each gas molecule there&#39;s a very large difference so in charge cannot be transferred to such a large distance so what we do is when we increase the pressure it means we are trying to bring the molecules very close by decreas remember 10^ minus 2 means I have removed the excess of gas which can interfere okay so the particles are very close to each other so now since they are very close to each other this hydrogen molecule can easily transfer his charge to a nearby molecule so this increases the conductivity for a gas that&#39;s why they can trans for charge so when R for did this experiment he further reduced the pressure which okay and now let me remove this part but what RF for did is raford made some holes in this ano and then he covered the backside of anode with a floresent material Flor and materials are those material that emit light when they do not receive any source for example like in your childhood you would have uh radium watches that when you uh let them when you let them in the sunlight for some time they glue in the dark those are fluorescent materials that absorb the light and that later emitted floresent material like zns zinc sulfide so since the pressure is very low and he discharg charge the electricity to it the entire gas starts glowing the entire tube starts glowing not just near the cathode but the entire tube and then he figured out the places where he had made holes there are C made holes okay here he observed some marks exactly at the places where he had made the holes these shiny okay these shiny bright spots shiny bright spots were exactly at the places where he had made the holes in the anod okay then he come up with this idea that since the rays are coming from the cathode and and ending up at the anode and anodes are positively charged by Nature so this means that the particles that hit the anode were possib negatively charged since the particles pass through this holes and hit exactly at the spot where the zinc sulfide was covered in a straight line this means the particles also travels in a straight line clear yes sir okay so the cathode rays consist of negatively charged particle known as electrons why because cathode rays traveled from cathode to anode since anode are positively charged so only negative particles get attracted to the anode that&#39;s why we call them negative charge or called as electrons okay cathode rays travel in a straight line because we got the marks exactly at the point where we have made holes in the anode with the speed order of 10 to the^ ra 7 m per second and they produce Shadows of the object play in the path okay what does this means this means okay you each one of us have Shadow because we are material particles we are material particles light cannot pass through us that&#39;s why we get Shadow so if cathode race makes shadow of an object this means they are also material particles material particles that means they can be blocked by a human being or an object so that a shadow is C clear yes everybody clear or doubts so that I understood sir 100% sure yes okay if any doubt uh someone is hesitant to ask me directly please answer in the public uh private chart now cathode rays can pass through thin layers of metal since they can pass through thin layers of metal which means they are very small in size very small in sides cathode rays are emitted from the S surface of the cathode and their direction is not affected by the position of the anode so no matter matter what if you are placing an anode here and the cathode is here or if the anode is here they&#39;ll always travel in a straight line no matter what clear because because and this can be confirmed using a zinc sulfide R so cathode rays have high kinetic energy kinetic because everything that moves have kinetic energy in them so cathode rays are moving particles that&#39;s why they have high ktic energy why because kinetic energy is given by half M v² and they have large velocity of the order 10 the^ 7 m/ second so they have large kinetic energy they exert mechanical pressure on an object for example if in the tube you place a mechanical fan here of metal or plastic whatever you do if you start the experiment you see this fan starts moving in the direction it will start moving from one to other and starts rotating this means that these particles are hitting the fan that&#39;s why they are moving and this is also a property of a material particle just like you hit a fan and it start moving okay they can produce heat when stopped by matter if they are flowing free flowing from one thing to another there&#39;s no issue but if something blocks them they transfer all of its kinetic energy to this object in the form of heat which leads to the heating of the object this we see in our microwaves our microwaves heat the food using this principle okay they can ionize any gas since this gas is all since they are already in the ionic form because of the high potential if they encounter any neutral molecule they will also ionize it they will also ionize it clear wa that share Char what uh how do the ion ionize the neutral okay how do the see okay how do the okay see this is the cathode and the gas that lying the gaseous molecule that lying closest to the cathode will receive the electric current first from this wire clear yeah okay and now there are tons of sorry there are hundreds of thousands of molecules of gas inside it okay so since they are closest to the cathode will get charged first because they are in directly contact with this cathode yeah since and now the charge transfer from this atom to this to this to this that&#39;s why the entire tube starts glowing okay if the charge is not transferred will still obtain a glow just near just like krooks obtain okay but Thompson prove that these G these molecules get charged and travel and charge anything that comes into their path so that&#39;s why the entire tube starts shining because of the large current because all of these particles are charged by these particle that lie near this to the cathode so basically they all share the electron right yeah they all sh they all have their electrons they don&#39;t share electrons the electrons are coming from that it&#39;s just transferring from one part to it&#39;s like jumping from one place to another oh okay okay okay now cathode rays are deflected since they are material particle they can be deflected just like you throw a ball to a wall it gets deflected back by electric and magnetic field cathod R can be deflected by electric and magnetic field because cathod Ras are made of electrons electron are charged particles and both electric and magnetic fields are also made up by charged particles and charge particles if they are having same charge or opposite charge this particle will either get attracted or gets deflected in both either of the cases the path of this electron would be changed so that&#39;s why they are deflected in electric and magnetic field clear yeah okay the cathode race produce fluocin fluocin as I explained is the ability to emit light even after the source is removed when they fall on certain substances like zns the color of the fluoresence varies with the chemical nature of the substance for example if you take a highly conducting gas other than hydrogen the amount of fluocin that will you that you&#39;ll absorb would be more the the the perforated tube will shine more brightly the cathode rays can produce a chemical change and thus they affect a photographic plate photographic plate just in your if you have seen in the older time we&#39;ve got photographic camera reels anybody seeing photographic camera reels anyone I have seen s be brown sheet of paper with some imprint on it oh yeah the brown sheet of paper the brown sheet of paper has a quoting of AGI on it silver iodite when it is exposed to Sun Sun contains the sun rise also contains electrons okay we commonly call them as photons in the form so the cathode R they hit the photographic film surface and it affects the color because the compound gets broken down into its ini to its ionized form leading to the different colors that you obtain for a photograph so cathode R produces chemical change because it can either decompose a compound or can allow a chemical reaction to occur that&#39;s why the effect of photographic plate the cathode race also Al produces xrays when they strike a metal surface of very high atomic number just like tungster this you have seen in your suria bu everybody have seen suria bulbs the one with this St rounded wire the yellow bus yeah so we have seen this type of in spon which are highly penetrating but remember the tone that we use in our homes is far is far less it is a combination of different Metals so it do not affect us much but when you go for an x-ray we use pure tone that releases x-ray that has the power to pen penetrate to our skins highly penetrating so JJ Thompson determine the EM value which is charge to mass ratio of an electron okay by studying the deflection of the cathode rays in electric and magnetic field he figured out the value of charge by mass is 17588 to 10 the power G8 Kum per G clear here I&#39;ll explain what&#39;s charge to mation why we need it yeah what I was going to ask that no I was I&#39;m going to explain I know I know you guys don&#39;t know this thing so I have to teach you okay so what does charge to mass ratio means so initially listen charge to mass ratio means how much charge you are giving for example this is the tube there&#39;s the cathode there&#39;s the anode how much of since you are taking a gas you are taking a gas of gas has certain volume has certain volume this means it has certain Mass so the amount of gas that you are taking how much charge does it produce okay how much charge does it produce that can be figured out by using charge by mass ratio since the electron is just being discovered we don&#39;t actually know the mass of the electron and we don&#39;t know the charge of the electron these both things are unknown to us but we do know the amount of gas that we are taking here clear clear clear yes okay so what JJ Thompson did he took out he took some amount of gas and recorded the Char that this gas producing so and when he he figured out that for each one g of gas that he has taken the amount of charge that he&#39;s getting equivalent to this Val clear for each 1 G of gas the amount of charge that we are getting is this that&#39;s why we are using charge by mass ratio because we don&#39;t know the actual mass of the Elon and the actual charge of the electron we are we have just discovered the particle but so the only thing that I control that the amount of gas that I am taking and the charge that I can get from this whole experiment these two things I can measure clear clear why we are using charge by mass ratio because it helps us to Quant how much amount of gas do I take to receive this much of charge how much current do I need to prod how much current it produces clear oh yeah okay so by charge by mass ratio JJ Thompson was able to explain that how much gram of gas you need to require to get a charge but he still didn&#39;t answer the mass of an electron the charge of electron since it&#39;s a material particle it should definitely have a mass so here we got micans oil Rock experiment the theory of this experiment is not in your cabus not in cabus we don&#39;t need to read it we just only need the conclusions so Mican soil drop experiment was the first helped in the first precise measurement of the charge of an electron this helped in the knowing the charge of the electron which is made by Robert a Milik the charge of the electron was found to be minus 1.6 please make sure you remember this value 1.6 10 ^ - 19 Kum an electron has the smallest charge known so it was designated as a unit negative charge because they originate from the cathode cathodes are negatively charged hence they are considered as negatively charged particle so after the O dment experiment we knew the charge by mass value we knew the cym ratio and now I know the charge of the electron so this using this formula I can directly figure out what is the mass of an electron so the charge of an the mass of electron given by the charge that it has one electron divided by the E by m charge by mass ratio do you guys have studied Dimensions physics okay so let me open up this formula for you so mass of electron divided by charge of an electron divided by E by m value so if I open this e divided by multip by m can you see the dimensions the dimensions of a mass are left yeah okay so when I divide the charge that it has carry and the charge each gram of gas that we have when we solved it we figured out that the mass of the electron is 9.1 10^ - 28 G or since SI unit is kg we converted it to this 9.1 * 10^ - 31 kg okay now I&#39;m taking two minutes so that if anyone has a doubt please ask me or something else regarding me like am I going too fast uh my voice is my speech is not clear anything like this or if you have a doubt am I that good answer please the public chat yeah yes good I don&#39;t have any okay so and R yes sir s that I have a lot of Doubt regarding you I&#39;m not sure if you are if you know okay okay this is called this 9.1 is called as the rest mass of an electron rest mass of electron when the electron is is not moving the mass of electron when it is moving with a low speed we can calculate using this formula okay this is called reduced Mass Al there are other formulas for it too where the m not equals to the mass of the electron when it is at rest when the velocity B is the velocity of electron C is the velocity of light and M is the relativistic relativistic means relatively we are checking it with respect to the speed of light clear so remember when an object travels with a higher speed its mass gets considerably low when an object is dy is moving at a faster speed the ma its mass gets decreased clear if you have seen drag racers or F1 cars you have seen those cars sometimes gets pulled upward when they are driving at a very high speed because of this this is given by Theory of Relativity by was Albert Einstein okay when you apply this formula we see if the object starts traveling at a higher speed okay its mass will get decreased since mass is inversely proportional to velocity velocity of the object since C which is speed of light is constant it do not change so it will not have any effect on the mass of an object okay so if the velocity decrease okay when Mass decreases the velocity increases and when you try to put up a molecule very fast like if you reach it to a velocity of infinity the value of M1 by B becomes nearly zero this means at this point the mass of electron cannot be found clear the results are not that important we only need to remember this part and this formula please clear yeah okay so an electron is defined as a subatomic particle carrying a negative charge of this value one unit negative charge and has the mass this into if it&#39;s not okay that&#39;s wrong it should be 10 the^ minus 28 okay and this mass is equals to 1 by 8837 time the mass of the hydrogen atom which is 0.549 a okay now we are moving forward to discovery of protons the positive race it was done by Goldstein what it did it did the same experiment that JJ Thompson did but instead of making holes at the anode this time he made holes in the anode oh sorry in the cathode he made holes in the cathode and covered the side of the cathode with the source and material like zns he took up a gas it put up several thousand volts of current and he realized and he observed the same thing that he observed with the cathod r they also travel with straight line but they originated from the anode they travel from anode to the cathode and leave the same marks just like the cathode race since they originated from the positive side they are termed as positive Rays Canal Rays or sometime also as anode Rays the same experiments just the opposite thing okay okay again we came across the same thing specific charge by mass ratio for Canal R varied with the nature of gas what be figured out that the charge by m value for Canal race changes every time you switch to a different gas for different gases like H2 helium helium uh oxygen nitrogen for this the electrons the cathode charge by mass ratio value do not change for the cathode ray charge by mass value do not change it remains same for each and every gas but for the C anode Rays the C by m value changes every time you change the gas changes with the gas every time you change the gas so the nature of the gas and was found to be maximum for the H2 why maximum because e by M the mass is since hydrogen is the first element since it has the lowest Mass so the lowest denominator makes the largest fraction that&#39;s why it says the maximum charge by mass Val the positive rais particle then thus called as positive charge gaseous atoms that are left after the removal of electrons or ionized gas atoms for example so in the tube we in the tube we got anode rays which are positively charged and how this will be produced like for example if you have the H2 gas this high potential stripped the electrons of the hydrogen molecules converting it to either this form or maybe decomposing the gas clear the high potential that you applied manage to strip of electrons from this hydrogen molecules or may it may have decomposed the gas to its Elemental form to release the electrons that hit the anode on this side clear clear okay however if H2 gas is used in the discharge the positive Rays particles are named as protons since we have used hydrogen gas which is the lightest has the highest charge by mass value we call the these partic positively charge particles as protons which is called as P so the atomic particle that constitutes all matter is called as proton it has mass 1.6 10^ - 27 and charge equivalent to electron clear so which of the following is heavy which of the following is a heavier particle which of the following is a heavier particle proton proton why the numbers numbers s and RI is it clear to you why proton is heavier can you repeat again which of the following is the heavier particle mass of electron and mass of proton which of the following is what sir heavier okay sir it is the mass of proton I believe uh the mass of proton it&#39;s heav because the negative power means it&#39;s in fraction so the larger the denominator smaller the fraction that&#39;s why okay summary what we have written now the charge by mass ratio for the proton is given this mass of one mole of proton one mole of proton means 6.022 the power 23 proton atoms so mass of one proton multiply the Avogadro number Na and we get the mass 1.76 10^ minus 3 in form of kg the radius of proton which is your nucleus is 1.53 10^-3 CM also sometime written as 1.5 1.5 F FM and 1 FM for = 10^ -5 meter clear it&#39;s your s it&#39;s your unit of measurement for 1 feter = 10 ^ - 15 M and the radius of proton usually lies in the range of 1.2 to 1.5 FM FM the volume of proton since we are assuming that it is a sphere the volume is given by 4x3 pi r CU and on solving the putting the value of R we got the answer 1501 ^ minus 38 the charge on the positive Rays is usually one but it may be +2 and + three depending on the type of gas that you are using okay in older time times the television picture if you have seen the big televisions they have a fluorescent light tubes that are called as Cod tubes okay those tubes are used to produce the image on the TV in the older times using the fluos the light tubes called as cathod tubes that&#39;s how okay now further okay this is the part for both neat and I earlier model of atom the first model of atom we have is Thompson okay based on Thompson Thompson did found the particle called electron Goldstein found about the proton and Thompson found electron Goldstein found proton so and when they both concluded the experiment the charge of electron the charge of electron was nearly to the equal to the charge of proton since they both are part of an atom JJ Thompson come to the conclusion that the nucleus is made up of both proton and electron JJ Thompson concluded that and at okay when we figured out the fundamental image of the particles constituting an atom everybody started fighting what what would be the structure of atom since dton said the atom do not have a fixed structure okay so JJ Thompson used the criteria for the charge of proton equals to the charge of electron to derive to devise his model of atom so after the discovery of proton and electron Thompson proposed a watermelon like model in which the atom is considered as a sphere with net POS positive charge spread across the watermelon like the red part with the electrons distributed just like we have the seeds of the watermelon okay within the square of radius 10 the power minus 10 m to give the most stable electrostatic agreement okay this model is also be represented as a pudding or a cake with a positive charge with raising electrons embedded in it a major point of this model is that the mass of an atom is considered to be spread uniformly across the atom the plus that you are seeing is are the protons and the electrons are embedded in it okay what does we mean the most agree most stable electrostatic agreement we mean that the charge of elect neon is nearly equals to the charge of proton Thomson said the atoms are neutral particles neutral particles this single line was the reason today we are studying about Thompson Thompson&#39;s model of atom although this model has various flaws but this single thing that tells about the neutrality of mod the electr neutrality of an atom made was an important thing that we needed to consider that&#39;s why we are studying Thomson&#39;s model of atom today but okay what are the issues with Thomson model of atom the Thompson&#39;s model of atom fail to explain how positive and negative charge electrons are arranged how they are arranged it cannot be randomly filled it also feel to explain the atom stability for example if positive and negative charge are staying this close to each other there should be a exchange of energy in between them but we know that atoms are stable particle because if they are continuously sharing the energy in between them we would have been experiencing some kind of phenomena throughout our life but in our life we see we don&#39;t see such kind of phenomenas okay the theory did not mention anything about the nucleus of item it do not told about the arrangement of proton how they are arranged how their electrons are arranged what is the how different elements have different proton Arrangement or not and it was unable to explain the scattering by the RF experiment okay remember JJ Thompson found electron Goldstein found proton and Chadwick found NE can you scroll up slightly sir okay yes sir continue yes okay so JJ Thompson found electron Goldstein found proton and ched found Neutron okay so JJ Thompson&#39;s student was Goldstein and Goldstein students were shed all of them got Nobel Prize both student and teacher now what did RF for did ra for conducted an experiment okay Le for conducted a series of in experiment using alpha particles alpha particles are your doubly charged helium atoms sorry helium ions W charged helium ions are called as alpha particles commonly shown as h2+ they are your alpha particle a beam of alpha particle is directed against a thin tin foil of gold platinum silver or Co the foil was surrounded by circular fluent zinc screen like znl whenever an alpha particle stricks the screen it produces a flash of light okay this is the experiment setle uh setup he used okay this is a radioactive element radioactive element and it is the source of alpha particle it produces a alpha particle species so what Goldstein did he took up a gold foil this is the gold foil he put it bited in a very thin fine sheet and this is the collyer also called as col meter collyers is a substance that help us to direct turn the beam into a single fine line so the source has producing alpha particle that are are going in different direction but some particles passes through the small Screen through the Coler and hits the gold fil so around this gold fil there are number of fosen materials and these part these alpha particle found to scatter in different directions okay the transmitted Beam with no deflection that came goes straight to to the sheet a there are some that deflected to sheet B and there are some that deflected towards the sheet C so during this experiment LEF figured out that most of the alpha particle passed straight through the foil without any deflection that means most of the alpha particle were hitting the Cent relation sheet a and some of them were deflected by a small angle small angles like this this is a small angle hitting b and a very small number of which is one particle in every 20,000 particle did not pass through the field but suffered a rebound which is a 180° deflection which means this particle went straight hit up the gold foil and went back to the source okay so what are the conclusion that we can draw from this experiment since most of the particles for hitting the sheet a we figured out that most of the space around an atom would be empty why helium particles are positively charged so this means if there is a positively charged Center somewhere in an atom where the proton lies and they are positively charged only proton will deflect this positive charge because positive charge refs the positive charge so most of the particle positive particle State went from the Alpha from the gold shield proving that most of the space inside the atom was empty that&#39;s why they pass straight now some of the particles were deflected through their original part through moderate angle like okay like from this picture we see majority of the particle that hit the sheet a pass straight through the atom and the particle that suffered deflection they hit they were near the positive charge space where the proton was lying and that&#39;s why they are deflected from their Direction and the particle that directly hit the POS in the line of the direction of the proton was sent by 180° back okay clear everyone clear can you scroll up okay okay so now okay considering this Rond came to a conclusion that most of the space around the nucleus is empty okay and he came up with the formula R is = to R A to the power is 1X 3 where this a is mass of an element mass of an element that you are taking okay you figur out and the r not he found was .52 angrong one angrong means 10 to the power - 10 m okay so you figur out okay this R not is the radius of suppose this is your first shell this R not is the distance between the nucleus and the first orbit and the first orbit which is 0.52 angrong clear if you see the nucleus was having a 1.2 fir me distance which is around 10^ -5 M but the radius to the first orbit is 10 the power 10 m which is a difference of 1 lakh times so this means if there is a nucleus the first orbit is around 10 L times further from the nucleus clear this further proves that the distance around the nucleus is empty clear clear oh yeah okay can does anybody like to take a guess how much one L distance means around if I would like to explain it in a real life can you assume the what does one lak times means how farther it would be I think almost towards USA almost almost goes to USA it&#39;s like you are sitting somewhere in South India let&#39;s for example let&#39;s go for kyak you sitting in Kumari and I&#39;m mas and the distance to the first orbit is is more than the North Pole is more further than the North Pole clear the first orbit Li this part that&#39;s why most of the alpha particle pass straight through the nucleus okay explain briefly how other Force scattering is a particle by Target nucleus provide information on the size of nucleus okay considering the nucleus as a sphere it will have a some kind of volume the mass of the nucleus would be m whatever since there is a nucleus it would have protons so whatever the mass of the proton have or if the electrons are lying inside of it the total mass would be M and the radius of the nucleus are since this is the if this is the nucleus the distance would be R so the total distance for R not is given by 1.2 for me to 1.5 which is the r radius of the nucleus since if it&#39;s a hydrogen atom the nucleus would be small and during the uh anod experiment we found that number that the posit sorry that the anode Ray values anod Ray charge by m value varies as you change the gas so for a heavier atom the charge by mass r value would be lower it will be lower now so the radius of the nucleus will also vary with the mass because there will be different number of protons and electron that would be residing inside this nucleus we are still considering JJ Thompson&#39;s theory that proton and electrons are lying inside of each other okay now J rather for discarded this thing why since if proton and electron would be existing coexisting inside the nucleus the alpha particle that is coming towards the nucleus the electron should be able to hold it the alpha particle should be attracted towards the nucleus but it was repelled by it that means the electron and proton cannot lie in very close to each other so that means the electron must lie outside the nucleus the electron lie outside the nucleus and the nucleus mass and the radius of the nucleus would vary according to the change in mass given by the formula R is = R A1 by 3 where a is the mass number so density is of a nucleus is given by mass by volume mass is the mass of a single proton multiply total number of protons divided by volume 4x3 p r Cub putting the value of r as R A1 by 3 RQ would be equals to r q multip with a can you repeat again sir okay let me remove it first okay now I need to find the density of a nucleus okay so density is given by mass by volume Vol mass of a nucleus is given by how many number of proton does it have and the mass of one proton this would be the mass of the nucleus now okay and the volume is 4x3 piun R Cub 4x3 &lt; R but we know r = r a^ 1 by 3 yes sir so R would be r 1 3 3 yeah yes just how do we get that r = r a 1x3 okay r = r 1x3 is derived by brother for this is the formula that you need to remember we are not deriving this formula this formula was by okay okay okay so for this three removes three and we got 4 by3 pi r q a a cancels a this three goes above and we I got DS 3 m which is the mass of one proton sorry and 4x3 Pi are not Q so if you clearly see the density of this nucleus do not contain any Mass terms for a nucleus this is the mass of the nucleus it do not contain the mass of the nucleus the atom it only contains the mass of single proton clear yes everybody clear yes sir okay so since this is many this is missing this a value is missing this proves that the density of a nucleus is independent of inde dependent of mass of a nucleus so if you have a iodine atom which has atomic mass 107 and if you have a hydrogen atom which has mass one they both will have same density they will both have same density irrespective of the atom they have so this proves that the density of a nucleus is independent of its mass number a the volume of nucleus is directly proportional to the number of nucleons constituting the nucleus but how many number of proton does it have but the density won&#39;t change the density won&#39;t change means what okay density is mass by volume suppose this is a nucleus since protons are adding with increase in atomic number the mass is increasing clear everybody clear so the density should also increase but when the number of protons start increasing in the nucleus the nucleus also increases its volume to accommodate this much number of proton inside because these proton also repel each other they also repel this repulsion increases the size of the nucleus which in turn increases the volume okay so the mass increases and at the same time the volume is also increasing so the density that is increasing by the increase in mass is cancelled by the increase in volume clear that&#39;s why the density of the nucleus do not change remember the density of a nucleus is constant everybody clear please answer me or at least please reply in chat when I ask please yeah it what about the rest two yes yes sir you sure you guys don&#39;t have any doubt okay okay now the where I was I was discuss okay the discovery of neutron by Reser for model of atom so when RES for was doing his experiment there are also some particles that were emitted by the react further it he further combined this experiment with different elements so while doing Chad okay there was James Chadwick that bombarded berium with the stream of alpha particle and he observed that the penetrations were not affected by electric and magnetic field that during this the Barum there are particles that are helium particles that are hitting the berum atom so there there should be the certain uh there should be signs like Sparks that we have seen on zinc that we also saw in Beria but we only saw particles in a straight line let me show you what happened is he constructed a this was a tube there was a source that striking alpha particle and there was a berum when alpha particle strike there were two magnets nor Pole and South Pole these particles hit if okay when the particles if there were electrons they would be deflected by there would be an no R deflected by another magnetic field if they were protons they were again deflected by electric and magnetic field but the particles that hit the this zns surface were hitting in the straight line they weren&#39;t affected by this presence of magnetic field that these magnets were applied so Chadwick came to a conclusion that there are also apart from electron and proton there is also a particle which is neutral which do not have any charge also constitute a nucleus since it by do not have a charge because if it had charge it should be deflected by electric and magnetic field this is the reaction and he called these particles as neutrons which means neutral particles the mass of neutron is given by 1.6 10^ - 24 kg okay the proton wait the proton okay the proton have nearly mass of neutron so that is nearly equal to the mass of the proton th a neutron is a particle having Mass this approximately 1 AM U or nearly equal to the mass of proton or hydrogen atom whenever I say hydrogen atom I&#39;m considering both one proton and one electron and when I say proton only I can also write proton as H+ which means it only contains one proton zero electron okay and it carries no electrical charge so it has the charge to m ratio as zero clear yes okay now I&#39;m ending the class here today if anyone has a doubt please ask I don&#39;t have any doubt and uh this topic is very boring last class were most more fun last class what was more fun it is Theory yeah it&#39;ll take some time to build up a chapter I&#39;ll also I also have some questions regarding this that I know for sure you guys won&#39;t be able to solve even if I show you show you the solution to it but it&#39;s it will take some time for this chapter to build and look what I&#39;m telling you the whatever part we have read today is just the History part remember nothing will come in your exam from this part nothing except except except for this one part which may have a potential chance uh where is where is is where it is where it is where it is where it is uh this one formula and apart from this this that raford Pro that the D it of an of a nucleus is independent of the atomic mass of a substance okay these are the only two points like I said the chapter is currently building the important question that that you can receive in your exam will come from the quantum mechanics part uh quantum mechanics I have tons of questions okay so don&#39;t worry it&#39;ll be fun but I need to cover the History part first because I can&#39;t something I had to give an intro so we have a class tomorrow I&#39;ll make sure I&#39;ll have some good things for you and some questions too we are starting with the model of item once finished we&#39;ll go for the quantum part and discussing the items and all once the theory part is done we&#39;ll purely focus on questions okay what&#39;s your thought I have no doubts no one has doubt it was just Theory like I said it&#39;s not that complicated you have studied in class 9 and 10 the model of items still the same thing nothing much the only thing you need to remember from today the density of the atom is independent of atomic mass the only thing you should remember about it for the past course of years the questions from this part have reduced even after 1990s there is no such question regarding the that I have that they have asked from this topic after 1990s there is no question literally after I guess 1998 there&#39;s no question from this topic till now because it&#39;s Theory complete Theory it do not since it&#39;s history and it&#39;s no longer used so they focus mainly at questions from the quantum Parts because that is currently used and we are currently exporing the prospective of quantum so should I end the class if no one has a doubt just answer yes in the chat and I&#39;ll add it yes sir okay thank you e e e e e e e e e

Transcript for:Structure of Atom Lecture

Transcript for:
Structure of Atom Lecture