Atomic Structure Bohr's Atomic model 1

Added: 2026-05-12

[00:00:00]so students last class we did the rutherford's atomic model you have seen the drawbacks of the other force atomic model so rather for could not say anything about the stability of an atom all right it was challenged by maxwell and his atomic model was discarded you can say that and also rutherford could not explain anything about the different types of series the atomic spectrum and all those things which you'll be studying in the higher classes so to say so we could not explain about all those things now coming today today's topic rutherford's student was neil bohr now neil bohr was a danish physicist all right danish physicist we can say that neil bohr was clear so uh not a chemist let me tell you physicist because this chapter is there in physics also atomic structure now what he said got it listen carefully so he said that we are having a nucleus which consists of the neutrons and the protons which is positively charged and around the nucleus we are having shells all right shells not clls s h e l l s cells all right around the nucleus we are having different shells which we call this as energy levels all right the shells he called it as energy levels energy level we can say that or we can say it has orbit we can say that clear so he said that we are having a nucleus where the definitely as i said you the other four discovered nucleus the most of the mass the entire mass of an atom is concentrated here because it consists of the neutrons and protons and electrons is moving around the nucleus in a shell which is having a definite or a discrete amount of energy this they are also called as energy level we can say that okay they are also called as energy level and this energy level was also designated means it was also named like as you can see this is your first shell this is your second shell this is your third shell in this way we can have fourth fifth five sixth seventh up to seven we can have because there are seven periods in the periodic table later on when you study the periodic table you will come to know that number of periods corresponds to number of shells you cannot have infinite number options understood maximum you can have seven okay fine so the first shell was named as the first shell was named as k shell we can say that the second shell was named as l shell l then m then n in this way went on the first it started from k now you may ask why it starts from k why neil bohr was not playing abcd or what he could have started from a b c d y started from the middle that is k now k has come from the what you can say latin language k means kernel k e r n kernel and in latin kernel means it is first in latin language kernel means it is first so answer is k l m n o p in this way it goes on put it now white started from the uh what you can say letter k in this way the first shell he named it as k shall the second is l third is n m n in this way it goes on okay now remember it what i said is this is energy level so the shell which is nearest to the nucleus near the first shell which is nearer to the nucleus it has got a definite amount of energy a fixed amount of energy it has got a fixed value of energy you will study about it in class 11 that what is the fixed value of energy it is generally it is nothing but in calculated as minus one three one two kilojoules per mole the first the energies now you may ask from where i got it now this is not there in your this one you will be studying the higher classes so e n is equal to minus two pi square m e 4 z square by n square h square this is the formula isn't it now pi 22 by 7 m is the mass of the electron which i said already 9.11 in 10 to the power minus 31 kg e is a charge of an electron which is 1.602 in 10 to the power minus 19 coulomb z is the atomic number last place i said you number of protons is equal to number of electrons n is the number of shells energy level and h is your plant's constant you'll be studying about it a planck's constant that is max planck was a scientist who gave a value of constant its value is h is 6.626 into 10 to the power minus 34 joule again so all these value when you will put it and the value of n is one you will put it n is one the first shell which is called as the energy in the ground state the first generalist all right so you will be getting the value to be as a first shell the first orbit we can say the value will get it as minus one three one two kilo joules per mole you can see that now here many of you asked what is mole mole is nothing but a unit which is used to measure the what you can say or which is used to relate between the different atoms molecules ions gases then solids liquids in chemistry lab all right because in chemistry lab we are using different kinds of substance like see when you are going to a market you are buying eggs what is a unit to buy the eggs dozens you are buying potatoes what is the unit kg gram in this way suppose you are buying oil isn't it you are buying in what liters suppose you are buying pen you are banking words scores numbers scores so you can see different substances have got different units but the unit which you are using in our the substance which are using your day-to-day life the unit are not interrelated it has got no relation with one another like a liter of petrol has got no relation with potatoes potatoes has got no relation with dozens of eggs nothing they are all independent of each other but listen carefully in chemistry in chemistry the solid liquid gas atoms molecules ions whichever you are using in the chemistry lab they are all interrelated because the numericals are there the problems are there upon it for example suppose if i ask you if i ask you based upon this let me tell you a little bit about modes then you will come to know let me ask you suppose a given reaction is there zinc solid plus h2so4 which is aqueous aqueous means liquid dilute gives what it gives you znso4 which is again a solid and hydrogen gas is released a gas so you can see one particular reaction in a particular reactions already is there liquid is there gas is there three things are there are we having an attended life these things in one particular wording and say reaction first of all are we having an education reactions no so the units are independent of each other they are independent of each other as i said you suppose if you want to buy potatoes should you know that what is that dozen of eggs or the relationship there is any relationship between dozens of eggs and potato or there is any relations with potato and the pen is there any relationship in pen and the petrol no nothing they are all independent of each other so we did not have to know the relationship but here it is required how is it going suppose if i ask you that i am giving 5 gram of zinc i am giving you you tell me how what is the volume of hydrogen gas evolved so there is a relation between gram and liter or milliliter this relationship suppose i am giving you 5 gram of zinc i am asking you you tell me how much of sulfuric acid is required what is the weight of sulfuric acid required to react with five gram of zinc again this relationship in mass and mass all right in this way there is a relationship in one particular equation you can say solid liquid gas is there i can ask you the number of atoms you will be doing this sort of questions when you go to higher classes between number of atoms number of molecules and all those things you'll be doing these questions so mole is now listen carefully so mole is that particular unit i'm not saying the definition of mole you learn in higher classes a mole is that particular unit which establishes a relationship between the substances used in a chemistry lab relationship between what's already liquid gas like as i said you 5 gram gives how much volume of hydrogen to get this you need to convert into moles then only you'll let simplistic relationship all right you will be establishing a relationship and by using that relationship you will be able to solve this particular question so again i repeat mole is what mole is nothing but a unit mole is nothing but a unit which is used in the chemistry lab which establishes a relationship between atoms molecules ions solid liquid and gases again let me tell you this is not a definition this is just a simplification of the mode all right i'm not defining mold i'm explaining you what is more definition you read it later on but it's understood what is that mole mole means a unit here kilo joule per mole is what what is this it's nothing but a unit it's a unit all right like in our day-to-day life as i said two different units are there similarly in chemistry lab also there must be a unit which establishes the relationship between solid liquids gas atom molecules and ions so that is a unit i hope you understood a little bit about it more all right now next is as i said you that by using this formula by using this formula that this formula was given by neil bohr it was experimentally calculated and this formula was being taken out it is not there in now in your level but it you did not have to know about all these things so when you put the value of all these things which i said you value of h value of n n s one if you put it m the mass of electron charge of electron atomic number pi value will put it then you will get the energy of the first shell the first level which is minus one three one two kilojoules per volt and this energy is considered to be as the energy in the ground state that means is the minimum amount of energy remember it alright it's a minimum amount of energy clear and as you are going from the first shell to the outermost shell the energy what happens increases energy is increasing all right energy is increasing remember that when you are going from the first shell to the outer muscle the energy increases so electrons for that reason which are present in the outermost shell they are known as valence electron because outermost shell is known as the valence shell what i said you valence shell the outermost shell is called as a valence shell and the electrons which are present in it they are called as the valence electrons and always remember that in a chemical reaction the valence electrons only participates in a particular reaction all right in every chemical reactions the balanced electrons only participate linear motion electrons they are not participating in it why because inner motion electrons which are present inner motion let us say this is outer moisture these two are the inner motion now they are held strongly by the nucleus why because nucleus positive electrons is negative so there is an attractive forces but what happens to the outer muscle the outer emotional electrons are free so to say they are considered to be as free electrons while free because i said the energy is maximum so if the energy is maximum where what what you find is that they are free these electrons are and hence they are liable to lose from the outer moisture so every chemical reaction whenever it's taking place whether the loss of electrons suppose it is going to take place from the outer muscle suppose electron if it is going to gain if the outer motion is going to gain then the electrons is gained by the outer motion suppose the shearing which is going to take place between the two atoms during chemical combination that is taking from place from the outer moisture so outermost shell determines the chemical reactivity of an atom the outer motion that determines so hence that particular shell is called as a balance shell so the valence shell determines the properties of that particular atom whether the atom is a metal non-metal inner gas metalloids and whatever it is how it is if the number of electrons in the outermost shell is one two three it is metals because it has got a tendency to lose how i'll tell you if the electron if the outermost shell has got five six seven then it is non-metals all right if in the outermost shell it has got h that is considered to be as inert we can say that inert in nature because outer motion is fully filled and if it has got four electrons in the outermost shell four four now one two three means it has got a density you lose it is a mentals five six seven tendency to gain it's a non-metals we can say non-metals and four means it is a metalloid because it can lose or it can gain either it can lose or gain so it is considered as metalloids you will come to know when i finish this particular chapter everything will be clear don't worry about it all right and age means it is inert means outer moisture is fully filled it can it will neither lose nor it is going to gain electrons fine let me come again back to the postulates so the postulates means the points which i was talking to the neil board's atomic model so what i said you he said that the first is a k then l m n in this way energy increases as you're moving away from the nucleus energy is increasing so the electrons which are present in the first shell it's considered to be the lowest energy after that the energy increases what is the value i said that this is the value this energy considered to be in the ground state correct and remember one more thing that when an electron is present in a particular shell it neither loses nor gains energy it neither loses nor gains energies so if an electron is present in a first shell it will continue to remain in the first shell only unless and until you provide energy to it or it loses energy all right listen carefully if an electron is present in a particular shell it continues to remain in that particular cell with a fixed amount of energy it continues to remain unless and until some energy is being provided externally or it loses energy all right it will remain in that particular shell remember that so neil gore suggested that when an electron is present in a particular shell it neither loses nor gains energy all right it neither loses energy continuously nor it gains energy continuously it has got a fixed or a definite amount of energy so it remains it continues to remain in that particular cell unless and until some energy is provided so when some energy is provided listen carefully now if it gains energy but it will do it will jump it will not move use the word jump from lower energy level to the higher energy level by gaining energy very simple means by gaining it will jump from low to higher and by losing energy it will come from higher to lower by losing energy it will come from higher level to the lower level so the change in energy delta e is equal to e2 minus e1 e2 is definitely greater than e1 we cancel that e2 is greater than e1 here if it is jumping from lower to higher so it is gaining energy see two minus even if it is coming from uh that is it is losing energy then it is come from lower but you can say high to lower then it is going to lose energy we can say that clear in this way now next is the energy level is discrete you you can't see the energy level understood you don't you don't see the nature it is not like a concrete that you will be seeing this is discrete discussed means what hidden chipper what a discrete and the value is quantized quantize means what fixed the value is context the fixed value of energy okay more about it i'll say in the next video thank you