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0:00 challenges and problems are fuel of victory so yes my victorious students i welcome you all to this awesome platform of physics voila as you all know we have already covered our first chapter that is some basic concepts of chemistry so today we are going to start our next chapter that is structure of atom so students as the name suggests the whole story is going to revolve around a single word that is atom as you all know we have covered dalton's atomic theory in the previous chapter what was dalton's atomic theory
0:47 according to that theory atom is the smallest indivisible particle but students in today's lecture we will see that there are various scientists which perform particular experiments and will let us know that atom is not the smallest indivisible particle it is further classified and is made up of three fundamental particles now what are these three basic fundamental particles now let us move towards our first topic that is discovery of fundamental particles the three fundamental particles which i am talking about is
1:32 electrons protons and neutrons so the concept that dalton's atomic theory gave us was wrong and was proved by various scientists now let us see the first discovery the discovery of our first fundamental particle which is electrons the discovery of electrons also known as the study of cathode rays it is also known as study of cathode rays why it is said to be the study of cathode rays
2:18 because students we will see that in experiment performed by william crook in which he took the crooks tube what he did he took the crooks tube taking the tube about 60 centimeter long and two electrodes were kept in that now let me show you that william crook took this crooks tube this tube is known as crooks tube why it is known as crooks tube because the scientist that was performing this
3:04 experiment his name was william crook that's why now in this side cathode is taken and on this side a nod is taken right here it is a vacuum pump okay now here it is applied with voltage now students the basic three conditions which we need to remember during this experiment was that high voltage was applied why high voltage is applied see basically what happens is in this tube they took hydrogen gas what they did in
3:50 this william in this william crooks tube they took hydrogen gas now as you all know that gases are poor conductor of electricity so that's why we took high voltage to conduct the electricity to perform the experiment and to see the discovery of electrons so here high voltage is required high voltage is required moreover low pressure is maintained in the tube right you have to also maintain low pressure now what was the experiment we are going to see one by one once i am telling you again see two electrodes are taken they are sealed
4:37 from both the ends right hydrogen gas is inserted inside it and high voltage is supplied here why high voltage is supplied to provide it and to conduct the electricity because gases are poor conductor of electricity now according to the experiment students firstly they took high voltage nearly about 10 000 volts the second thing the gas that they took had the pressure about 1 atm here the gas had the pressure about pressure was about 1 atm right okay the next thing what they did was vacuum pump was applied there to maintain the pressure you know they applied vacuum pump to maintain the pressure to build up the pressure inside
5:24 when this condition was there when pressure was about 1 atm the thing that they observed was that no current was flowing when high voltage was there pressure was 180 m no no current flows right okay now when students when they decrease the pressure when they decrease the pressure and the pressure was about 1 mm pressure right at that spot what happened students current started flowing now here current started flowing when when the pressure was reduced
6:12 right students now see these you can see this is the current that is being started flowing and a colored glow was also observed here colored glow was seen right now what happened was that these colored glow was also seen and the current was flowing but we were unable to see that what is the thing that is coming from this side to this side now because the speed was very fast the pressure was against reduce to observe what is the thing that is coming from that portion to this portion now when the pressure was again reduced and the pressure was about 0.01 mm at that spot
6:58 students now these uh the cathode rays now were not visible hence to make them visible we inserted a perforated a nod what was perforated in order an odd is like perforated an odd refers to as a node in which a hole is present through which something can be pass on that is perforated or not so here one perforated anode was built up so that the rays could pass from here and when the rays were being passed from this end to this end what was seen on the spot on this end a greenish glow was being observed now see as i told you when they were moving when the pressure was about 1 mm pressure then we were unable to identify
7:45 which rays are coming and from which side they are coming and to which side they are moving on to observe this very clearly we reduce our pressure when the pressure was reduced we have to find the rays their charges their mass and so we observed that after applying the perforated anode a greenish glue was observed so at that spot students what happened at that spot greenish glow appeared right okay now this was the basic experiment which leads us and explained us that something was coming from cathodic and towards enordic anodic end and that's why if it was referred to at
8:32 cathode rays because it was coming from cathode towards anode so we discovered about cathode rays that's why when we speak about the discovery of electron we refer to it as discovery of cathode rays or the study of cathode rays because the rays which were coming from cathode are referred to as cathode rays now how can we compare electron with cathode rays this thing arised in our mind and so jj thompson according to his experiment gave us that the properties of cathode rays are similar to that of electrons and so he compared both of them now what were the properties of cathode rays the very first property was that they can travel in the straight line how they had proven that students you can see that
9:18 whenever a solid object was placed in the path in the tube the shadow was seen and when will be the shadow scene when you put some light over it for example i am standing in a path right you put a torch behind me so a shadow will be seen the same was seen and observed in the case of this william crookstroke crooks tube what was seen that a solid object was placed and a light source was passed on so that a shadow was placed over now if the rays are traveling from behind that and will move in a direction toward forward then only this could happen that means cathode rays are traveling in a straight line are traveling in a straight path right so the number first
10:04 thing the property of cathode rays is they produce a sharp shadow of the solid object placed in their path this shows that cathode rays travel in straight line students now the very next thing is that the next property that explains us that cathode rays are made up of material particle or they have some kinetic energy was explained by the paddle wheel if a paddle wheel is kept in the william crooks tube what was seen that it starts to rotate it starts to rotate hence they possess some kinetic energy or we can say that they are built up of some of the material particles here you can even add that they possess they possess
10:51 some kinetic energy that is why it leads the wheel to rotate to move right so the second property is if a light pedal wheel that of mika mounted on excel is placed in their path the wheel begins to rotate this shows that cathode rays are made up of material particle now moving towards the third property what was observed students in the third property it was shown that cathode rays carries negative charge and electrons are also negative charge hence we can compare both of them okay so how was this proven this was proven because as cathode rays were negative charge when a particle is said to be negative when it is
11:37 approaching towards positive right because positive and negative both attract each other while negative negative or positive positive repel each other so when it was seen that the rays were attracted towards the posit positive path it concludes us that it is negative because negative is always approaching towards positive if it was already negative then it would have been repelling each other right so here when an electric field is applied on the cathode rays they are deflected they move towards the positive plate of the electric field and when something is moving toward positive it is already a negative thing so cathode rays carry negative charge this proves that they are electrons right so here was
12:24 discovery of electron proven to us now students the next property which tells us about the cathode rays is that when a magnetic field is applied see when we first applied electric field we got to know that they carry a negative charge when a magnetic field is applied during this process these rays are deflected in direction which shows that they carry negative charge so it's all about the way in which they travel and towards which they deflect right here they deflect towards the positive end hence they are not as negative they are also they are deflecting in such a direction hence they are referred to as negative charge right so see in this in this diagram you can clearly see these are the cathode rays that are being traveled
13:09 right after applying the electric field here this is the electric field that is being applied okay when the electric field is applied it is moving in the disk in this direction when it is moving in this direction we can see the positive end is towards upward so it is moving towards positive if it would have moved to a downward that means it is moving to a negative but negative negative repel each other hence when it is moving in this direction it depicts that it carries negative charge now coming towards this diagram i am showing you that magnetic field is applied from the downward direction so what we are observing here when the cathode rays are traveling this is our perforated anode which carries a hole now cathode rays are traveling from in between them now it is moving in a path where it is getting positive so hence it concludes
13:57 that it is already already a negative charge because it is moving towards a positive charge now coming towards the further next properties of cathode rays we could say that cathode rays are basically they possesses heating effect because what happens is when cathode rays strike a metal foil it becomes hot that means they produces heating effect now students the next property is that they cause ionization of gas through which they pass that means ionization means refers to as that it's split into ions right so it ionizes the gas right the next further point is they produce x-rays when they strike against the surface of hard metals the x-rays are
14:43 produced now what are the hard metals like tungsten molybdenum right or uh phosphorus and or fluorescent substances such as zinc sulphide x-rays are produced in that case now the very next property is that they affect the photographic plates also and the last property is that they possesses penetrating effect now what do you mean by penetrating effect penetrate means to move inside something okay they can easily pass through thin foils of metals they are stopped only by the metal foils of greater thickness otherwise they won't be able to stop they could totally penetrate and move from inside towards outside right so these were the properties of cathode ray students which was observed by jj
15:30 thompson with the help of william crooks experiment now students coming forward to explain the charge and mass of electron first of all we are going to see the charge to mass ratio now what do you mean by charge to mass ratio and how it helped us in calculating the charge of electron in calculating the mass of electron so there were two experiments that was performed now the number first thing was done by j.j thomson what he did he did that he took cathode he took perforated anode please mention here perforated anode is taken again i am explaining you perforated refers to as when our anode has a hole in between so that a particular race could travel through in and out right
16:17 now students what happened is these are our rays that are being traveled from cathode towards their node now according to j.j thomson two kinds of field were applied one was the electric field and the second one was the magnetic field that was applied why is what it was applied to calculate the charge to mass ratio that's why students now let us see this when he applied electric field electric field was applied in this direction right positive and negative you could easily observe that as you all know cathode rays are negative charge so they will move towards positive charge according to the experiment so you will see a a spot when you will see a spot when electric field is applied the second most thing you
17:03 should observe is when magnetic field is applied now magnetic field is applied from below so when magnetic field let me write here it is electric field it is electric field so it is striking towards the a point right okay and when it is magnetic field which is applied from uh the downward direction it is the spot c where our rays is being stride so this is our magnetic field and spot b refers to when both are equivalent when both are equivalent that refers to the b spot now what do you understand from the following diagram what are we getting here is students
17:48 that when both the fields are applied then jj thompson calculated charge to mass ratio he he took different electrodes he took different gases and then he saw that charge to mass ratio charge to mass ratio was same when different electrodes and different gases are taken now what was the value that was observed in all and they were same the value was about 1.76 into 10 raised to the power 8. this was the value and the unit were cooler per gram right it was same when different electrodes and when different gases were taken before this experiment when william crook performed it he took only a particular kind of gas that was
18:35 hydrogen gas and he applied different pressures and he observed that but now what did jj thompson did he took different electrons on both of the ends and he took different gases inside them and observed that right students so the specific charge you know specific charge of electron is independent on the nature of gas do remember that also now this was charged to mass ratio that was being observed according to this experiment which was being performed what was the basic things that were kept in mind of j.j thomson he saw that he saw that the deviation like it is moving towards a it is moving towards c it is moving towards b these deviations usually depend upon the three basic factors what are the three basic factors
19:22 number one is the magnitude of the negative charge on the particle the next thing is the mass of the particle okay the particles mass the third thing is the strength of the magnetic field right how much magnetic field you are applying to them now these are the basic three things due to which we could see the deviation towards a the deviation towards c or the direct path towards b these three factors are responsible for that now students now these all things which i've already told you are being written here let me dictate it to you when electric field is applied deviation from path takes place we have seen the deviation it is moving towards a right if only electric field is applied cathode rays strike at a right if only
20:08 magnetic field is applied cathode rays strike at c in the absence of any field or when both of the fields are equivalent they strike at b the rays strike at b right okay now students according to the experiment which is done with the jj thomson we got to know about the charge of electron we got to know about the charge of electron with the help of charge to mass ratio right and the charge of electron was about minus 1.6 into 10 raised to the power minus 19 coulombs right okay students so this was our charge of electron now to calculate the mass of electron one more experiment was performed that was milliken's oil drop
20:53 experiment now what is milken's oil drop experiment as the name suggests it was performed by milliken and oil drop experiment refers to as that we are taking oil droplets now how to take oil droplets an atomizer is kept atomizer contains oil droplets and the form of mist it is being applied right in the form of mist in this atomizer oil droplets are kept these oil droplets are sprayed like this now what happens is this is the inner section of the chamber that i have shown you through the help of this diagram you can see that there are two basically plates present here this is the plate which has a small hole in between and the lower plate is negatively charged these two plates are
21:41 kept in between this structure right now what happens is students you have taken a telescope here to observe what is happening inside and on the other hand you can see the x-ray from the source x-ray here is kept to provide the ionization you know to provide the electrons right okay now what you have to observe is you are observing that when atomizer you spray the atomizer in such a condition that oil droplets in the form of mist travel inside now when oil droplets are traveling in the form of mist they have to travel they have to travel from this hole from this particular hole they have to move down right how will they move down one by one yes one by one the oil droplets will move towards downwards now what is happening
22:28 students oil droplets when they are moving towards down downwards the x-ray from the source liberates electrons the oil droplet is now surrounded by electron for example this is our oil droplet these are now surrounded by electrons when these are surrounded by electrons the oil droplet is unable to move towards downward why it is unable to move toward downwards because downward is a charged plate which is already negative and negative negative repel each other okay so negative negative which will repel each other will push the oil droplet towards the upward position but what happens is students the gravitational force brings the oil droplets downwards so two forces are happening here one force is like
23:15 electrostatic force one is like negative negative are repelling each other another one is gravitational force so due to this condition due to these two fields would which are being held here we are able to calculate the charge and mass of electrons and when we are able to calculate the mass of electron it came out to be 9.11 into 10 raised to the power minus 28 grams okay so this was our mass of electron and this mass of electron was about one by one eight three seventh of the mass of hydrogen you know so this was the most important concept which we need to keep in our
24:00 mind and so we can define electrons as electron is that fundamental particle which is negative charge now understand first the definition then we'll elaborate it right electron is the fundamental particle which carries a negative charge and whose mass is equal to 1 by 1837 of the mass of hydrogen now splitting it definition into the following types one by one i would say that electron is a fundamental particle why it is said to be as fundamental particle because it is responsible for the formation of atom we already understood that atom was not indivisible right it is further divided into three categories so we got to know the fundamental particle term now it has negative charge from where this term
24:46 came negative charge it came from the discovery of cathode rays we started there that it carries a negative charge okay the next very next thing is that it has a mass which is nearly equal to 1 by 1837 of hydrogen it came with the help of milliken's oil drop experiment so we can now define electron in a very good definition right so this is the millikan's oil drop experiment which i've already explained you step by step now let us read it to make it more clear in the experiment some final droplets were allowed to enter through a tiny hole into the upper plate of electrical condenser now this is the upper plate okay and with the help of atomizer we were spraying the oil droplets in the
25:31 form of mist they were traveling and they were allowed to move so that they could enter through the very first plate right okay these oil droplets were produced by atomizer as i have already told you the air in the chamber was subjected to the ionization by x-rays right students okay the electrons produced by the ionization of air i already told you that x-rays are going to produce the electrons now they will surround the oil droplets right okay electrons produced by the ionization of air attach themselves to the oil droplets now this will cause and leads towards the calculation of mass of electron right thus all droplets acquire negative charge now they have negative charge around them right okay
26:16 when sufficient amount of electric field is applied the motion of foil droplets can be accelerated now we will see the motion of electrons right or made stationary what we can do is like we can increase its motion we can decrease its motion or we can make its motion stationary almost still right okay millikan observed that the smallest charge found on them was about 1 minus 1.6 into 10 raised to power minus 19 coulomb now this is the charge of electron right and the magnitude of electrical charge q on the droplets is always an integral multiple of the electrical charge that is q is equals to n into e where n can be 1 can be 2 can be 3 now here q refers to as the charge
27:02 you know they are saying that the magnitude of electrical charge q which is present on the droplet is always an integral multiple of the electrical charge that the electrons are carrying clear the oil droplet which has a charge will depend upon the charge of the electrons that are surrounding them so this was the millikan's oil drop experiment which helps us to calculate the mass of electron now students this was the discovery of electron we will proceed toward the discovery of a proton it is almost similar to the discovery of electron just the basic difference will come in the charges so students proton was discovered by goldstein and during
27:48 the discovery of electrons there were some things that were quite different from discovery of proton what were these different things that are being observed first of all is the charge electrons are negatively charged while protons are positively charged how can i say that positively charged particles are protons this is also concluded by the same you know crooks tube how in this particular tube you can see both of the discoveries the discovery of electron as well as the discovery of proton first of all don't get confused with the previous diagram in the previous diagram on this side we have taken cathode on the other end we have taken a nod but in this diagram students we have done the opposite i have taken cathode on the other side and anode this side now if i talk about the
28:33 discovery of electron if i take a thought from that side that means the rays are going from that end towards this end that means if i am taking this red pen i would say now these are my cathodic rays if i take a thought on that spot and an odd on this spot then that means the rays that are coming from cathode towards anode are cathodic rays right so these red ones are our cathode rays which explains us about the discovery of electron always remember these things which electrode you are considering on which side like in previous case we considered cathode this side now we are considering cathode that side this is all concept that's it nothing else okay now cathode rays
29:20 already started now what are our discovery of protons or i would say canal rays for protons we are using canal rays or anode rays now what are these anode rates just opposite to cathode rays if our cathode is basically the negatively charged then our anode is the positively charged why not is the positively charged map because you know atom is basically a neutral you know it is neutral neutral refers to as the total positively charged and the total amount of negatively charged both are equal if there is something negative then for sure there will be something positive also so if there is something negative that means if there is cathode rays present then there is something positive which is our enordes
30:07 which is our canal ray students now what are the canal rays here or what i would say is the uh is our anodic rays see cathode rays are the one that traveled from cathode towards a nod hence the opposite will be an order is other one that will travel from another towards cathode now this is our anode as the diagram is just opposite to the previous one so an order is other one that is going from anode towards cathode and it is seen that during the discovery of proton when the rays when the anodic rays which move from anode towards the cathode strike on this zna screen strike on this zna screen okay and here it is observed here it is seen
30:53 on this zns coating you know it is being seen that some rays are coming from anodic side and so they referred to as anode rays or canal rays hence they are coming from anodic side they are positively charged particles because cathode rays are negatively charged particles now the properties of proton what are the properties of protons number first property of proton is that they carry positive charge they carry positive charge okay now what will be the second category they produce heating effect students they produce
31:42 they produce heating effect okay now the next property is that they travel in straight line right they they travel in straight line it is also been proved how they travel in straight line if you keep object in their place they will produce a shadow effect just as similar to that of electrons so they also travel in students straight line okay now they are deflected by magnetic field
32:36 you know during the discovery of electron we already told that they are deflected by magnetic field why because they move in direction towards the positive end now they will move in the direction towards the negative end because they are positive in nature right okay they also possesses kinetic energy the next property is that they possesses kinetic energy now students these were the properties that we started in the discovery of proton but the thing that was different from electrons is that in electrons i already told you that students our specific charge with that we started in electrons that was independent of the nature of gas but in protons it is dependent on the nature of gas and also one more thing students in electrons we
33:23 have studied the charge by mass ratio in electrons for different gases and different electrodes were same but in the case of protons they are not same right so these were the basic basic and little little things that are different from each other now students comes the charge and the mass right if i talk about a charge of electron if i talk about the charge of an electron let us make some let us make a box here and write in it okay firstly we are going to write the charge of elect charge of proton students the charge of proton is same as that of electron it's just that electron is negatively charged so negative sign comes in front of it and proton is positively charged so positive
34:10 sign comes in front of it that's it that is the same thing you know positive come and the numbers are same 1.6 into 10 raised to the power -19 coulomb this thing is almost the same as that of electrons in electrons what is the charge on an electron minus 1.6 into 10 raised to the power minus 19 coulomb but in proton what we observe is positive 1.6 into 10 raised to power minus 19 columns right now students this was the charge now what is the mass right we are going to write the mass of proton students in electron case we have seen that the mass of electron was 1 by 1 837 of the mass of hydrogen now in the case of proton if i ask you about the mass in the case of
34:57 proton it is same as that of hydrogen atom it is about 1.6 into 10 raised to the power minus 24 kg right so here it is almost same to that of hydrogen 1.6 into 10 minus 24 kg students this is the mass of protons clear students these two things you need to remember in all of these three cases like in case of electron in case of proton in case of neutrons so this k this was the discovery of proton which we have seen that they are positively charged they have charged almost similar just the sinus sign is different and yet the mass is also different from that of electron students one more thing how would i define proton as i defined electron in the same way i'm going to define proton
35:43 proton is that fundamental particle now fundamental particle are those particles which stated as that matter is not indivisible it is further divided you know into electron proton and neutron so the basic definition is always starting like this that proton is a fundamental particle which has a positively charged how positively charged because it is coming from anode towards cathode you know we have seen they are going from anodic side towards the cathodic side so they are positively charged and hence their mass is almost similar to that of what hydrogen atom so this is going to be the definition for the proton students now as we have studied the discovery of protons so one thing that each and every student need to keep in their mind is that always think like a proton why because
36:31 proton is always positive so positive thinking students is very very necessary for any examination whether it is your boards whether it is your competitive any exam if you have positive thinking in your hand if you have the control over your mind that you need to think positive every time in every situation in every challenge then you can accomplish anything you can gain victory any time okay so the continuous you know repetition of your work repetition of your questions when you solve any question when you lose your confidence just remember think positive think like a proton that's it clear so discovery of proton taught us
37:16 to think like a proton now coming towards the discovery of neutron students the neutron discovery you know it was given by chadwick and he explained us that when alpha particle was bombarded on beryllium alpha particle is what alpha particle is our helium right this is our alpha particle when alpha particle is bombarded on beryllium what was observed neutron was produced so students neutron was produced by the bombardment of alpha particle on beryllium and this experiment was done by chadwick so what we concluded here we concluded that neutron is basically neutral that means it has no charge right and what it is mass mass is that similar to that of
38:03 proton that means when i come to define neutron when i come to define neutron i would say that neutron is the fundamental particle which has no charge mass is equal to that of hydrogen atom okay
38:49 now let us also write the definitions for the electrons and protons so that you can keep in your mind right okay if i talk about electron electron is the fundamental particle which has negative charge and whose mass is whose mass is equal to
39:34 1 by 1 8 3 7 of the mass of hydrogen atom mass of hydrogen atom and last is our proton right last is our proton so what would be the definition of proton i would say that proton is the fundamental particle is the fundamental particle which has which has positive charge
40:20 and whose mass is whose mass is equal to that of hydrogen atom that of hydrogen atom right so students kindly put a star mark over here and do remember this and do remember this because it is going to help you in your examination these three definitions please put a star mark over it or write in your ncrt so that you can remember the charge and the mass over these three fundamental particles right so this was the discovery of our
41:07 fundamental particles now we are moving forward towards the atomic models now as you all know we have discovered that atom is divisible and we have already started the fundamental particles now what is the atomic model atomic model refers to as the basic structure which defines us that how does an atom look what is the representation of an atom students the basic concept for the atomic model was done by thompson and thompson just saw this atom and he remembered watermelon he remained he remember the raisin pudding model you know so he compared it with the watermelon and he said that that atom is basically a
41:53 positively charged species in which electrons are embedded just like a watermelon in which red portion is the positive one and the seeds which are embedded in between them are the electrons so this was the comparison which he did with atom and with the watermelon so that the people could understand the basic structure of an atom and hence he defined the positively charged particles and the negatively charged particles he said that the negative charged particles are electrons while the positive ones are the other regions you know other than electron and this concluded that the whole atom is neutral because the total positively charged is equal to the total negatively charged so this was the basic concept that you want the people to understand
42:39 that atom is neutral in nature right so the first thing that he concluded in his model is that atom is neutral atom is neutral the second thing he said that is electrons are embedded in the atom just like seeds in watermelon seeds in water melon right he also concluded that atom is
43:27 full of positively charged species in which electrons are present i want to conclude that this is the positively charged species in which electrons are embedded i am talking about this i am not talking about the whole portion of an atom whole it is electrically neutral okay whole it is electrically neutral but i am talking about the portion that the other region is positive and some of the region where like seeds are embedded they are electrons right now it failed why it
44:13 failed because it could not explain the scattering experiments that were performed by rather food now what is the rather force catering experiment that helped us to understand about atom according to the rather food atom rather force catering modeling experiment according to the definition or according to the word i would say skatering refers to as when a ray is passed okay when array is passed it gets scattered it get deflected in its path it doesn't go straight that refers to as catering or that refers to as reflection right now what happens is a radioactive source was taken radioactive source was taken and alpha particle was splitted out from that now the beam of alpha particles these are the beam of alpha particles that are moving right the beam
44:58 of alpha particles strike over the gold foil and what is being observed here some of the particles goes straight some of the beam of particles are going straight while some are deflected with a certain angle some are deflected with a certain angle while students some are reflected back what is seen that some of the beam of alpha particles passes straight through the gold foil some of them are deflected through a particular angle while a very very very few are deflected back now what is this condition why is it happening it is going to make us understand about the atom all we are getting here the conclusions will help us to understand the structure of
45:45 atom how i am saying c if i make let us make an atom here for example this is my atom right if i consider this is an atom right according to the rudder rutherford model of atom what he said that most of the rays passes straight now see what i'm doing is most of the rays are going to pass straight okay these are the ray students that are passing straight okay these are the rays which are almost 99.9 percent which are passing straight now comes the next ones now comes the next ones which are
46:31 deflected by a particular angle now these are the rays which are deflected by a particular angle right the green ones are few less than the white ones okay but they are deflected by a small angle and then comes the last one then comes the last one which comes and are deflected back which are going in this direction but are deflected back now what is the conclusion you are observing in this structure we are observing that in the center most position in the center most position here
47:17 there is something that doesn't let this yellow line to cross over it what is this what does it refers to as it concludes that there is something there something mass is present in between this atom that lets this yellow rays to deflect back to its mean position it refers to add that atom contains some heavy particle inside it now what is this heavy particle that is present inside it and why it is not present all around it so from here we conclude that students the rays which are passing straight explains us that atom basically has empty space around it one by one i'm going to explain you the white portion explain us
48:02 that there is a lot of empty space present in an atom okay we are going to write it one by one so it will be easy for you to understand right number first thing you need to write is conclusions or observations you can do we could write observations that could be a much preferred word observation so whatever observations the observations were that atom has empty space inside it inside it in the bracket you can write because
48:49 99 percent 99.9 percent raise pass straight because 99.9 race parts pass straight that's why it explains that there is something empty space this area you know from where the white lines are being passed now comes the green one areas that they are being reflected why they are being reflected that means you know alpha particles are basically the positively charged species right and reflection is observed when when a positive strike towards the next positive right so that means at the center most position there is something positive that's why when something is coming nearby it gets deflected what is
49:36 it it is explaining to us it explains to us that the center of atom is positively charged is positively charged as some rays are reflected by small angles okay now the third conclusion the third conclusion is the raise the yellow one is the race the yellow one it concludes us that there is something heavy present inside
50:22 it because if i'm moving from this direction towards this direction if i have someone of you know my weight so only i could be pushed back to my mean position if i have someone who has very much less weight than me then i could you know push him or her away and move toward forward direction right so there must be something that could compete with me in my direction that means there is something heavy present inside it that is pushing it and doesn't letting it towards to move forward so we could all say that this center most position of the atom which is known as nucleus is heavy you know so all i can say that the center is heavy the center portion is heavy or we can
51:07 say the nucleus is heavy because this rays are deflected back these are summaries very few rays very very few rays are reflected back clear students so these were the observations that we made from the rutherford model of atom now students now students according to this diagram i have shown you a single atom you know now it also explained it to us about the two parts that atom basically consists of two parts what are these two parts nucleus and the extra nuclear part now these two basically is the conclusion that we make
51:53 from this model now what are these conclusions first of all comes the nucleus as you all know nucleus i have already told something is present at the center and it is heavy that means nucleus is present at the center and it is heavy and students nucleus if it is present at the center i have already told that the center of the atom is positively charged hence we conclude number first we conclude that nucleus is positively charged nucleus is positively charged this i've written positively don't get confused positively charged right and if nucleus is positively charged nucleus basically comprises of neutrons and protons you know it comprises of neutrons and protons because basically if i talk about electrons then you can see the charge on electrons
52:40 and the charge on the protons right if i talk about electrons electrons come under the area of extra nuclear part in the nucleus it is only the positively charged species neutron is neutron has no charge and proton has positively charged hence nucleus comprises of both of these protons and neutrons okay and it is heavy it is also heavy okay the second basic thing which we have observed is extra nuclear part extra nuclear part basically comprises of electrons that are revolving
53:28 around the nucleus or i can say they are embedded in the nuclear part electron basically revolves around the nucleus or they're embedded in the extra nuclear part that is other than nucleus so this was the conclusion this was the conclusion if you want to make the rather full model of atom in a very you know big way so you can make like this also so what i'm going to explain is the same thing that there are some rays that pass straight that explains us that atom basically has a lot of empty space inside it the second most thing that we conclude here are that you know some rays are present
54:15 that are being reflected by few small angles you know they are reflected by few small angles and there are students some rays that are deflected back there are some rays that are deflected back like this so these are the basic conclusions that we observed in the rather food model of atom okay so this was the model of atom now we are proceeding towards the very interesting topic of structure of atom that is going to be atomic number and mass number basically students to understand atomic number and mass number first we need to understand about electron protons and neutrons which we have already covered students we represent atomic number as capital z and
55:03 mass number as capital a so to represent any atom with the help of atomic number and mass number how will it show us see to represent it i am going to write an element x we are assuming there is an element x now i have to show atomic number and mass number over here so atomic number is always placed below as z and mass number is always placed at the above as a clear so atomic number is capital z while mass number is capital a now what do you mean by atomic number whenever we are arranging all the elements in periodic table each and every element is assigned a number which is known as atomic number basically atomic number is the number of protons
55:49 that is present in the atom okay so all i would say is atomic number refers to as the number of protons in any atom right students so all i can say is if it is z then it is equal to pp refers to as the protons now students i am talking about mass number mass number refers to as for nucleus how is nucleus comprised of you know an atom basically consists of protons and neutrons and electrons just revolves around them right so that means mass number is the
56:35 sum total of neutrons and protons right because electrons will be revolving around them so mass number which is represented by capital a is equal to number of neutrons plus number of protons students neutrons are shown by a small n while protons are represented by small p now as you all know that z is equal to p so in short you can write as mass number is equals to n plus z right now other than this comes electrons in neutral cases remember that in neutral cases
57:22 in neutral cases number of protons is equal to number of electrons neutral case refers to as when the charges are equal when both of the charges are equal when the charges are different the number of protons and electrons are also different for example if i talk about any atom sodium atom that refers to as a neutral compound but neutral species ah if i talk about sodium iron that means it has a particular charge over it and when a particle has a particular charge over it then we see that the number of protons and neutrons are not equal so at that case that is on not a neutral molecule so for a neutral molecule number of protons and number of electrons are almost same that means for
58:09 that case we can write that atomic number will be equal to number of electrons for what for neutral cases why because atomic number is equal to proton and if it is a neutral species then it is equal to electron as well so one of the examples if i would take is of carbon let us take a carbon now how to represent it in this form first i am writing in the place of x the carbon element alphabet c right now the next thing i have to represent is atomic number as well as the mass number i know that carbon's atomic number is what carbon's atomic number is you can see hydrogen helium lithium beryllium boron carbon it's six right the first 30 elements you need to remember so that it will be easy for you to understand the periodic table right
58:55 so it is a 6. now what is the mass number of carbon it's 12 mass number is 12. so if i ask you about number of electrons number of protons number of neutrons in this case what it would be i told you that whenever you see a species like this you have to first compare it this with it okay now x here is carbon that means we are talking about carbon atom the next thing is that z is being replaced by 6 z refers to as the atomic number so we can say that here atomic number is 6 here atomic number is 6 now if atomic number is 6 which is z z is always equals to number of protons hence i can say that in this case protons is equals to 6 okay now tell me about neutrons what is the value of neutrons to
59:40 understand neutrons we should remember this basic formula of mass number this basic formula of mass number mass number a is equals to number of neutrons plus number of protons so all i would say is a is equals to n plus b i have already found that p is 6 and a here this is a right so a is 12 and p is 6. if i take this here if i write in this form 12 is equals to n plus 6 so all i would conclude is n is also equals to 6 that means in this case number of neutrons is equals to 6 so i have already found mass number a which is 12 atomic number z which is 6 number of protons which is 6 and number of neutrons which is 6. now what is left out here is number of electrons now
1:00:25 students please tell me what what is the value of electrons here most of you have found that one of the lines which i've already mentioned here is in neutral cases when there is no charge given to you number of protons will be equal to number of electrons so we can conclude that if your number of protons are six then our number of electrons will also be equal to six so all i would say is electrons are also six here clear so in this manner you can easily find out atomic number mass number number of neutrons protons and electrons now let us take an example students calculate the number of electron proton and neutron in both of these cases the number first case is sulfate ion see the simplest form of carbon i have already told you now both of these cases are of charges if some
1:01:12 charge is present over it so how would you calculate electron protein and neutron in these cases first of all sulfate ion which is represented as so4 2 negative right see neutral species doesn't show any charge above but any species which have a charge is represented at the top of it like right here it is written minus 2 that means charge is there so all i can say is if i have to find out what is here the number of protons first of all i will find out number of protons how to find out number of protons we know that number of protons is equal to z which is atomic number so first of all in this compound we need to find out the atomic numbers for the particularly
1:01:58 elements right see here you can say that so4 comprises of like this i'm not taking this charge for once i'm ignoring this i'm just writing so4 now students a sulfur basically what does sulfur has atomic number sulfur has atomic number 16 while it has mass number 32. while practicing questions you will get to know and you will get to you know understand these concepts so sulphur has atomic number 16 as ma and mass number as 32 while if i talk about only oxygen i talk about here four oxygens are present in so4 i am taking a single oxygen for once to you to understand oxygen basically has atomic number eight and mass number as 16 right and i have a four oxygen here so if i take if i
1:02:46 consider if i consider only this sulfur only this sulfur what is the um atomic number here 16 which is equals to number of protons which we have already started and if i talk about oxygen what is that z here is 8 which is equals to protons okay so i have found for the case of sulfur the number of protons is 16 and for the case of oxygen the number of protons is 8 but i have seen that there are 4 oxygen atoms present here so i need to multiply it with 4 to find for all of the 4 oxygen atoms hence 4 into you know 8 is 32 so all i would say is that sulfur has proton 16 while 4 oxygen has protons 32 so total number of protons in so4 would be
1:03:32 here total number of protons would be it will be 16 plus 32 that refers to as 48 so i have concluded that there are 48 number of protons present here okay now please tell me what will be the number of neutrons here and what will be the number of electrons here students to conclude that to find neutrons we need to find what we need to find mass number because we know that mass number is equals to neutrons plus protons i have already found the protons value you know if i find the mass number value i can easily calculate the neutrons now let us calculate the a value that means the mass number value for sulphur the mass number is 32 it's
1:04:18 already shown for oxygen is it is 16 but how many oxygen atoms are present there total basically there are four oxygen atoms present there right students so all i could say is that if there are total four oxygen atoms present there so 4 into 16 plus 32 these are going to be a right so i would say 64 plus 32 is a 96 is a now mass number i have already found it's 96 but we need to calculate number of neutrons hence 96 minus protons will give us neutrons so i would say 96 minus 48 will give us neutrons because protons is 48 number so here we conclude that
1:05:06 48 is the number of neutrons right number of neutrons comes out to be 48 and number of protons also comes out to be 48. so we have already found that sulfate iron contains 48 neutrons and 48 protons and the number last thing that left is electrons how many electrons are present here as you all know students whenever we talk about charges if any if remember that if any negative charge is present over there you need to add that in the electrons if there is any positive charge present on the species you need to subtract it so here it is minus 2 that means i have to add it right in number see all i would say is for neutral i would say protons is equals to
1:05:51 electrons right if i consider this as a neutral then i would say protons is electrons so number of protons is 48 so electrons will be 48 but now i am coming towards my case again and i have negative charge minus 2 charge and i already told you if there is negative charge you need to add that number if there is positive charge you need to subtract that number so minus 2 will be added here hence we will find the number of electrons which comes out to be 50. so for this case we have already found that electrons are 50 protons and neutrons are 48 and 48 respectively right now comes the phosphate ion okay now we will see the case of phosphate iron students right okay
1:06:37 phosphate iron phosphate iron basically phosphate iron is po4 negative so students we have to do the case similar to the previous one what we need to do is individually first of all we have to calculate number of protons neutrons electrons for individual element then we need to add them together for the following compound right so what i'm going to do is i'm going to write phosphorus and oxygen individually first of all first we will write phosphorus here we will write oxygen so phosphorus basically has atomic number as 15 and its mass number is 31. if i talk about oxygen it has atomic number as 8 and its mass number is 16 right so now what we need to do is
1:07:22 we need to calculate number of protons and number of neutrons for both of these cases if i talk about phosphorus students so i would say number of protons is equal to the atomic number so protons here is 15 and if i talk about neutrons here so what is the neutrons atomic you know number which is basically referred to as protons so we can say that mass number is equals to number of neutrons plus number of protons here is the formula right if i have mass number a as 31 and if i have proton as 15 so what will be the neutrons i would subtract them so it comes out to be 16 okay if i talk about the electrons case here in the phosphorus what would be the electrons electrons will be equal to that of protons which is 15. now coming towards the oxygen part what is the
1:08:08 number of protons protons is equals to the atomic number atomic number is eight hence protons is also eight but students how many oxygen atoms are there four oxygen atoms are there so i will multiply it with four hence it comes out to be 32 for the case of oxygen only right now if i talk about neutrons neutrons what would uh it will be mass number minus z mass number minus protons 16 minus eight is eight how many oxygen atoms are there four so it comes out to be again thirty 32 if i talk about electrons for the case of oxygen i would say it is equal to number of protons i am not including the charge right now i am just doing individual element don't get confused at the end i am going to calculate that also so if we talk about electrons i would say 16
1:08:53 minus 8 is 8 right again it for 4 it will be 32 now student comes the calculation time so here you need to do is you need to calculate for all of them together like for po4 minus 3 right so if i talk about protons what will be protons for phosphorus it is 15 for oxygen atoms it is 32. it comes out to be 47 students it comes out to be 47 if i talk about neutron students neutrons for phosphorus it is 16 and for oxygen atoms it is 32 which comes out to be 48 and if i talk about electron students so if i count for phosphorus it is 15 while for oxygen it is 32 and there is minus 3 charge i already told you if there is negatively charged species then you have to add it
1:09:40 if there is positive then you have to subtract it so it is given minus 3 so you will add it plus 3. so what comes out here to be it's 35 plus 15 that's come out to be you know 50. so this is the correct value if i would say for number of electrons number of protons the number of neutrons in the case of po4 minus 3 claire students now comes the very interesting uh you know topic so students now we are doing isotopes basically all these terms contain the common word that is iso iso refers to as same so we are going to see something is same in all these cases right so first of all i am coming across isotopes as i said you iso refers to as same so isotopes
1:10:26 we see that when the atoms of same element please do note that atoms of same element have same atomic number but different mass number are referred to as isotopes atoms of same element have same atomic number same atomic number but different mass number so i am directly writing mass number as a so that you can understand we've already done that right atomic number i am directly writing as z so
1:11:11 one of the examples of these are the isotopes of hydrogen students hydrogen have basically three kinds of isotopes that is protium deuterium and tritiums okay so here i'm going to write it thrice because it's representation is with the capital letter h now students its atomic number is going to be same that is 1 but the mass number is different that is going to be 1 2 and 3. so this is the very first case the next example which we could take is of chlorine so chlorine has atomic number as 17 while one of the mass number is 35 and another one is 37 so these are the cases of chlorine so isotopes of chlorine are also very most important as and isotopes of hydrogen are also
1:11:56 important so you need to keep both of these examples in your mind right students okay now comes the next definition here which is iso bars again iso refers to as same so what is going to be same in this situation it is just opposite to that of isotopes but here we are considering different elements in isotopes we took same elements but in isobars we are taking different elements so all i would say that atoms of atoms of different element different element which have same mass number that is the capital a i am directly writing it
1:12:42 but different atomic number that is capital z so examples of this we can take is of argon potassium and calcium all of these have same you know mass number that is 40. while their atomic numbers are different for argon it's 18 for potassium it's 19 and for calcium it's 20 right so in all of these cases you can see 40 is there common and it is referred to as mass number because it is written on the top of the element and while we can see atomic numbers are 18 19 and 20 which are different in three of the cases right so these are refers to as isobars now students come the third definition which is known as isotones what are
1:13:29 isotones iso tones students isotones are those species in which the compounds you know in which the elements basically have same number of neutrons atoms in which same number of neutrons are present neutrons are present the rest of the thing you will see are different students one of the example is carbon and nitrogen i would take so you know if i talk about carbon it's atomic number is six and if i talk about
1:14:16 nitrogen its atomic number is seven if i take four carbon carbon its mass number is twelve and if i take off uh you know nitrogen its mass number is fifteen now we need to calculate the number of neutrons in both of these cases right if i take about the number of neutrons in both of these cases um i would take here the isotope of carbon which is carbon 14 you know just like we saw isotopes are those elements which have uh same atomic number while different mass numbers similarly carbon also exist in the form of isotopes so i am taking the element of that carbon which is the isotope so carbon 14 isotope and nitrogen 15 i am taking along with this along with this you can take off oxygen also as well okay if i take off oxygen this is the
1:15:02 case for oxygen so now you can see that 14 minus 6 i would take it is 8 15 minus 7 is 8 16 minus 8 is 8 right so number of neutrons that means mass number minus atomic number is neutrons right according to the formula which we did previous so we could say that in all these cases neutrons are equal again i'm telling you why i have taken isotop carbon 14 and why i have not taken carbon 12 because carbon can exist in both of the forms so to because carbon 14 is isotone to nitrogen 15 that's why i have taken this example okay now proceeding towards the next category that is isoelectronic students isoelectronics are the species which contain same electrons same number of
1:15:48 electrons right okay iso electronics refers to as same number of electrons same number of electrons basically example that we could take is of n a positive mg plus 2 al plus 3 right so these are the examples for the isoelectronic species all of these three contain 10 electrons right so students these were the cases for the iso you
1:16:34 know isobar isotone isoelectronics and so on so now moving towards our next topic all i would say is that there is one question for you you need to find out mass number atomic number protons electrons and neutrons right so students first of all we are taking the case for oxygen see for this oxygen it is already given to us about the protons right for protons i would say number of protons for any neutral species like its given oxygen for neutral species number of protons is always equal to atomic number right so all i would say is atomic number is also going to be 8 in this case the next thing that we always should remember is mass number is equal to number of protons plus you know number of neutrons
1:17:19 this is the formula right and here in the first case we have atomic number which is number of protons and we have neutrons also with us so with the help of neutrons and protons we can calculate mass number that means if i add protons and neutrons i am going to get the mass number and it is going to be 16 now so for this case the answer is 16 now number of electrons are being cast and oxygen is written alone that means it is a neutral species it is it doesn't have charge on it so hence we can say that number of electrons will be equal to what number of electrons will be equal to number of protons for a neutral species so here answer will be again eight right so this was all about oxygen now the next part here is about sodium ion students if i talk about
1:18:05 sodium iron sodium ion refers to as n a
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