Atomic Structure part 20

Added: 2026-05-12

[00:00:01]now already i've explained you the bohr's atomic model now few things more it is to needed to tell you about it that is as i said the board suggested that electrons is moving in the particular what you can say circular path which is considered to be as the shells or the energy levels or the orbits we can say that clear and i said you also that this energy level or the shells are the orbits which we can say it it is not discrete it has got a particular value of its own all right and it cannot be any energy level there are infinite number of energy levels possible between two energy levels there are infinite number of but you don't find electrons in those energy levels why because in those energy level energy is fractional and energy cannot be fractional why because the energy of a particular shell or an orbit is related to that of the electrons so electrons cannot be fractional i have told you are there also many times this particular electrons cannot be fractional so electrons is always found in whole numbers so how an energy can be fractional now how we can say that already i have told you about it also that that is e n that is n stands for what number of shells i have told you there are different shells is there and neil bohr also has given the name of the shells k l m n all these things i have discussed with you all those things all right clear so i told you also this particular formula minus 2 pi square m e4 z square by n square x square so you can see depends upon the number of shells here h is a planck's constant z is atomic number e is the charge of electron m is the mass of electron and pi is constant we can say that so if you put this value that also i said this value in terms of joules per atom it will be minus 21.8 into 10 to the power minus 19 joules per atom considering here let's listen carefully considering the value of zs1 and n and ns1 because remember it i told you earlier also that nilbort's atomic model was based upon hydrogen or hydrogen like species it was not based upon multi-electron species you will be studying this in the drawbacks of the nilboars atomic model you will be studying it alright so hence here the value of z has taken to be as 1 and n are taken to be as 1. suppose if you change the value of zs value of z you take it like 2 or 3 and n you take it any other value any other value you can take it let us say 1 2 3 anything then you will be getting the formula to be as in that case z square by n square joules per atom all right z square by n square joule per atom because here the value of z will differ and will differ but if it gives us one or n is one then i told you this particular value got it so this particular value or we can have minus one three one two kilojoules per mole again same thing z is one and n is one i'm taking it or minus thirteen point six thirteen point six electron volt per atom see i am giving y this particular values because questions can be in any what you can say units the energy can be going in any unit so you need to solve accordingly so you need to remember this value okay so hence this values are known as energy in the ground level in the ground level the first level is considered as a ground level in a particular atom we are having the nucleus and the first shell is considered to be the energy in the ground state because the lowest attainable this one this particular value the energy in the first state is considered to be as or energy of the first state i'm saying the first shell or the energy of the first orbit we can consider to be as this particular value clear the energy of the first shell so hence that is the lowest attainable energy the lowest attainable energy of a particular atom we cannot have lower than that because when you are going to rise higher when you are going to move from first shell second cell third cell for cell energy is increasing energy increases all right you put the value here n is equal to 2 for it n is equal to 2 here that one you keep it and any two any two put it so divided by four it will be this value will be so you know in negative the smaller value is bigger but i try to understand that so hence for that particular purpose when you are moving from the first shell to the outer muscle energy always increases so the k shell the first should always have lower energy all right the k shell or some lower energy then the l then m then n in this way it goes on so energy increases in this particular manner when you move from lower energy to higher energy means first shell to the outermost shell we can select okay first shells against the third cell in this way the energy increases so you understood this particular one this you have to remember it clear of course i said in other videos also just i'm explaining you because i thought that i need to explain little bit more about it you need to understand it so hence you can see that energy is not having any particular value any value of its own it has got a definite values hence it is said to be as energy is quantized now let me give an example of quantization let me just explain a little bit about quantization to tell you that what is the meaning of the word quantized for example suppose ah in us in our place it is not there suppose if you are going to uh different cities like suppose metro cities when you are going so you are taking a cab you can see in the cab a meter is there not at meter which so if you want to go certain distance it runs by meter whatever the price it has been shown by the meter that price you have to pay to that particular scavenger to the driver we can say that so what you find is that when you are when you are wearing a cab you will find it out in a car when you are doing it you will find it out the speedometer got it changes it may increase decrease gradually for example if 40 is there 50 60 again come back to 50 it depends on it upon the driving so the speedometer of the car changes gradually got it listen carefully the speedometer of the car the speed of the car it depends upon the acceleration and all those things it changes gradually it may increase decrease on on this things but the meter all right not the speedometer the meter which is being attached in the cab can you understand taxi might so many of you will not be following what is cab means it's a taxi isn't it a meter is there which shows that how much uh money you have to pay when you come down on it to a certain place already clear when you arrive to a certain place then you see the meter and you pay the money to that particular driver as i said so that it changes fixed according to fixed amount let us say that it is being fixed according to our rupee so after every rupee it changes what changes the value changes so there the value changes the value is quantized you don't have fractional value like you cannot have let us say two rupees ten percent no after two the next value will be three then after three it will be four let us say the meter the meter in the cab is fixed according to one one rupee the difference between this one one rupee got it or let us say difference is five five rupees or let us say differences ten rupees you know that if you go in metros and all those things if you just enter into the cab and you come down you have to pay a certain amount of money let us say 50 rupees is fixed so it starts from 50 then after that it goes or goes on changing so there it is quantized the value is quantized the value does not change gradually like 1 rupees 20 percent then 30 percent then 40 or it may come down to one rupees 10 per second no 1 then after that you can see the value 2 then after that you can see 3 after that you can see value 4 in this way that is quantized the speed is not quantized the speed changes increases decreases gradually the speed of the car the speedometer of the car but here this particular value is quantized which value that is the meter which is present in the car that is quantized that is fixed energy is fixed all right clear so in this way what you find is that that the speedometer changes gradually but the meter which is there or it by which you have the fair meter that is the tbs got it that changes what you can say to a certain value that is quantized it does not have any value of its own it does not have any fractional value it has it has been measured in that particular way you say no i will not give don't give no problem don't go to the car you go buy something else all right but that is being done that has been fixed in that particular way that has been changing in that particular way on you that has been changing all right so in this way it is being arranged the things are arranged in this particular manner all right fine now next after that that is the meaning of the word context means the energy is fixed it cannot have any fractional value or any value of its own so for that reason i said there are infinite number of energy levels between an infinite number of shells it can be theoretically possible theoretically possible infinite number of but in all the cells electrons does not exist electrons exist in that particular shell only whose energy is fixed whose energy is quantized all right and here also one word i am saying that you can see in the postulates it is given that it is stationary energy stationary it does not mean that the electron is stationary no stationary means the energy is fixed its value is fixed that is the meaning of the word station that does not mean the electron is stationary electron is moving around the nucleus which i've explained you and when it is moving and the nucleus nilbor has suggested that it neither loses nor it gains energy it continues to remain in the same energy level and it continues to have the same energy what the particular energy level has suppose if an electron is there in the second level then the energies of the electron will be that of the second level only it will continue to have the energy of the second level only unless and until you provide some energy or unless and until the electron loses energy if it is losing energy then all the energy is going to change if it is if you are providing energy from outside and only it will gain energy and energy is going to change otherwise if energy is neither lost or gained then the electrons continues to remain in the same level with the same amount of energy so for that reason it said that electron energy of electron is quantized it is fixed alright neil gore suggested that when the electrons is moving it is losing no it is not losing that is sorry rather force said that that particular thing but the neighbor said that no when the electrons is moving around the nucleus it is having some fixed value of energy and which energy whatever the energy level is possessed by that particular vertical whatever the energy is possessed by that particular shell the same amount of energy is possessed by the electrons present in that shell all right it's a clean up now next is what is the uh when the electron is moving around the shell got it so you can see it is a nucleus and that electrons is moving around the shell clear so what is the distance suppose electron is here in the outer moisture so i need to know the distance of the electrons from that of the cell that means i want to calculate the radius so how it is calculated r n is equal to a naught n square by z and against the number of shells a naught is a constant which is known as bohr's atomic radius bohr's atomic radius residues clear n is the number of shells z is the atomic number so what it is value 52.9 picometer a naught the value is fixed what is called as fourth atomic radius because if n is equal to one and z is equal to one so r one first is known as n and i saw that bohr's atomic theory is based upon hydrogen or hydrogen like species so if you take hydrogen then what is atomic number of hydrogen one so hence for that particular purpose here a naught is known as bohr's atomic radius which is considered to be s which whose value is 52.95 that is fixed this is a constant value a naught 52.9 kilometer all right how it is when n is one z is one then r one means first shell then radius from that of the nucleus is how much fifty two point nine kilometer accordingly as a number of shells is change z will change you will put the value and you will find it out the radius got it that you can do it now next is after that ah you can also calculate the velocity of the electron suppose electron is present in the third shell so what is the velocity of the electron in that particular so v naught into z by n v naught into z by n where v naught is again constant v naught is 2.188 into 10 to the power 8 centimeter percent 10 to the power 8 centimeter per second v naught again it is constant two point one eighty eight into the per eight centimeter per second see all this constant has been calculated experimentally by experimental determination dissolve this value is being calculated so v n means velocity of the electron in particular shell is given with the formula that is v n is equal to v naught into z by a similarly when an electron is moving around the shell all right it possesses angular momentum i have told it in the previous angular momentum one is a linear momentum when a body travels straight on the road that is linear but when you are traveling the circular path its angular radius angular velocity all these things you have reading physics or if not you will be studying in physics so in this way there we do not possess linear momentum we process angular momentum because linear momentum is momentum denoted letter p small p small p is equal to mass into velocity that is linear momentum all right here in case of angular momentum what we do we also take the radius so angular momentum is nothing but e is equal to mvr all right that is called angular momentum mind it you read it more about it in physics you'll be studying it so just like energy remember it neil gore suggested that angular momentum just like energy it is also quantized angular momentum is also quantized it cannot have any value and cannot have any discrete value we cannot have any fractional value it it's also having a fixed value why because as energy depends upon the number of shells or the e n is equal to minus two pi square me four z square by n square n square it depends upon the number of shells similarly we are also calculating the angular momentum of a shell of an orbit so it depends upon the shells so if it is depending upon the shells and how its value can be fractional it is never fractional its value is also fixed quantized so what is angular momentum is the formula m b r because m into is linear velocity linear momentum when you multiply r means why you multiplied r because electrons move in a circular path that is a radius which i have told you so m v r the formula is n h by 2 pi n h by 2 pi for example for the first cell first what is angular momentum n is 1 h by 2 pi for the second shell n is 2 2 h by 2 pi for the third shell how much which is 3 h by 2. how much is changing in whole number it is changing in whole number first is h by 2 pi then 2 h by 2 pi then 3 h by 2 pi understood so just like energy angular momentum is also quantized it cannot have any value it has got a fixed value we can say that now from where he got this particular value mdr is equal to nh by 2 pi neil bohr could not say we will be studying in the next but you can say ah concept will be studying it there i will explain you from where we got it in the d block this concept i'll be explaining you from where um what you can say neil bohr suggested us that mvr will be an h by 2 pi all right there is also another limitations of the bohr's atomic model the drawbacks of the bohr's atomic model but could not say see but the scientist who took it out he will say the how the scientist that is the knowledge they estimated it they estimated it and their estimation was correct their estimation was based upon observations of course they were not having the resources at that particular time to explain that how did he got this value how did they arrive to this particular formula the resources was not available that is a limitation of science i should say that now science is quite developed and now the resources are available from that resources we are able to find it out and when we find it out we find it out that whatever the scientist said got it whatever they estimated it is more or less correct as in case of nail bore got it you will see that many of the things which was estimated by the scientists now when we find it out when we derive it by experimentally we find it it's more or less like to see their estimation see their knowledge see their observation how accurate they are in their observations all right that you have to learn it you have to admire from this particular scientist that even if the resources was limited but still then by their observations they were able to get a conclusions and that conclusion when we match it with today when we are doing experimentally and we are finding it out we are finding more or less it is correct i don't say everything is correct but most of them in this correct that is the beauty of science and beauty of that particular scientist we should admire their knowledge we should admire their observations that how correct in their observations they were and that is we need to learn in science but we need to understand in science so mvr is equal to nh by 2 pi got it their energy is quantized we consider that it has not any value of its own but a fixed value we consider that here now next is i will say you that you have seen it e n is equal to minus 2 pi square m e 4 z square by n square x square this is a formula of second okay now the question comes here where from this negative sign comes why is negative why energy is negative from where it comes i will explain you know listen carefully now you know that when you're moving away from the nucleus listen carefully the energy increases the first shell is having some energy second cell is having greater energy thirds it is having written edge it is estimated or it is assumed that when the electron is present in the outermost shell its energy is arbitrarily taken to be as zero it is considered to be a zero when the electron is present in outer motion why all right because we what we say the electrons which is present in the outer muscle is the free electrons this ethernet the valence shell the outer muscle is a balanced cell and the electrons which are present in it are the free electrons you have studied in the lower classes because those electrons are participating in the bond formation whether it's ionic bond covalent bond or whatever it is in the chemical reactions only those electrons are participating so hence we consider that particular energy in the outer motion to be as zero and moreover when you move from negative i said you in negative the lower value is greater and i study what is that suppose it is having minus 131 kilojoules per mole after that when you are moving you are moving towards what zero because in negative if the value is decreasing means the the value increases so hence from negative to positive you are moving so negative to zero so hence it is considered that the electrons which is present in the outermost shell its energy is considered zero arbitrarily listen to my word carefully we are considering the arbitrary it is to be as zero now when an electrons is going to come from the outer most shell to the inner muscle it will not come by itself we have to do some work upon it some work has to be done electron has to lose some energy then only i've told you earlier that electron is going to lose and it is going to come from the outermost shell to the inner moisture it is going to lose energy it will not come by itself by losing energy what was the energy in the outer moisture zero after losing energy what the energy will be negative so hence it's considered that the energy is negative in the formula you get it negative this is one concept another theory you can say that when you are moving from the outermost should it spell to the inner motion the attraction is going to increase definitely because you are coming to the nucleus nucleus is positive electrons is negative so attractive forces increases when attractive forces increases when you are coming closer and closer and closer attractive forces increases you need to release energy then only you can come closer attractive forces increases but due to increase in the attractive forces some energy has to be lost then only you can reach to the lower energy level we can say that clear so hence when the energy is lost what was the energy in the previous zero when the energy is lost then what it is value is negative for that purpose its value is taken to be as negative for that reason in when we calculate the energy minus sign is put at the first we can say that understood now it's very simple when the electron is present outer muscle is energy is arbitrarily taken to the zero from the outer muscle the electron travels to the inner muscle it cannot travel by itself it has to lose some energy then it will come to the inner motion or when it is coming from the outer most in the inner muscle the attractive forces is going to increase why because it's coming closer and closer to the nucleus got it so as the attractive forces increases it is coming closer and closer to the nucleus what as what i said say at the attractive force increases energy is released energy has to be released then only the attractive force because due to increase in attractive force stability increases and stability is inversely proportional to energy if energy is less stability will be more got it all these things related and understand it so in this way when the stability will increase attractive forces increase it is going to lose energy and hence its value initially was zero as it is losing its value will be negative got it now so this is all about your knee boards atomic one thank you