 So, where we have we found out energy in the nth orbit for the atom in hydro for the electron in hydrogen atom is what minus of 13.6 by n square electron volt suppose it is not hydrogen it is hydrogen like atom then what will be the energy this into z is 5 this is for hydrogen atom for hydrogen like atom. Hydrogen like atom again has a single electron only energy in the nth orbit will be 13.6 by n square into z square electron volt fine where z is the atomic number. Let us solve few questions on it the difference of 2.3 electron volt there is a difference between 2 energy levels in atom. You have to find out what frequency will be emitted if electron makes a transition from first level to the other level getting it apply Bohr's third postulate what does it say difference in energy will be equal to a photon emitted and photon's energy is as into mu mu is asked delta e which is equal to 2.3 electron volt that is getting it. So, basically mu is equal to what 2.3 into 1.6 10 minus 4 minus 19 divided by 6.6 into 10 raise to power 34 you can roughly make it 4 and you can roughly make it 24 this is 0.6. So, this is 0.6 into 10 raise to power this is how much 15 to 6 into 10 square 14 hertz fine. So, this is direct application of the Bohr's atomic model third postulate. Now, if you talk about energy levels I mean this is not part of theory I am just analyzing the energy levels of the electrons then you will see that what formula says that energy in the nth level is minus 13.6 by n square even fine. So, what is the least possible of number principle part of number n 1. So, n is 1 this is a least n for the least n energy will be minimum or maximum minimum there is a negative sign every time you forget negative sign it is minimum for n equal to 1 it is minimum. So, n equal to 1 is also called ground state you cannot go below that fine. So, least possible energy happens when n equal to 1 or when electron in its ground state. So, e 1 is what minus of 13.6 e v e 2 is what minus 13.6 divided by 2 square electron volt how much is this 13.6 how much is this 3.4 exactly why you guys are so lazy why cannot you just calculate minus 3.4 electron volt if you shy away from calculation you will be completely shattered when you write the j a j ok. They test you on calculation also and especially these chapters which are easy they will put some difficult calculations find out what is the third energy level how much it is minus 13.6 divided by 3 square approximately 155 1.51 electron volt e 4 will get minus of 0.85 electron volt like this you will get ok. So, if you draw energy level diagram you will have least possible energy for n equal to 1 which is minus of 13.6 electron volt fine then you have for n equal to 2 you will see that there is a big gap between n equal to 1 and n equal to 2 energy this is minus 3.4 how much is this gap 10.2 electron volt fine next energy level is minus 1.5 ok. So, energy level this is n equal to 3 that is minus 1.51 next is what minus 0.85 one thing you will notice that the difference energy is reducing ok slowly and slowly then next level is coming closer and closer. So, n equal to 5 will be further closer n equal to 6 will be more close fine. So, like this there will be like till and tension infinity I mean slowly and slowly they coincide. So, after a point it does not matter what is the quantum number ok and anyways if you give it large enough energy energy tends to 0 right from this energy is going towards 0 and as soon as energy goes to 0 electron is free it is not bounded fine. So, that is what this is you can say energy level where energy is 0 and then the atom ionizes or electron leaves the atom fine. So, this is how you can see the energy diagram is now here is the thing if electron is in n equal to 4 level how many wavelengths it can emit it is n equal to 4 level. So, it can directly go to 4 to 1 one wavelength it can jump from one stable orbit to another stable orbit or it can go to 2 or it can jump to 3 or once this jumps to 3 then 3 will go to 2 and this will go to 3 or there is how many there is one more which one the electron is it n equal to 4 you cannot increase it which one this this has gone this has gone no it can go from 2 to 1. 1 2 3 or 6 are already there so 6 fine. So, you can see 6 wavelengths can be emitted if electron is at n equal to 4 excited state. In fact, when electron is at n equal to 4 it means what you can choose out of 4 you can choose any 2 transition will happen. So, basically 4 C 2 ways transition will happen right. So, if electron is in nth excited state so, it will be n C 2 number of wavelengths will be emitted. So, if you just know how many wavelengths are getting emitted you will be able to find out which excited state it is in fine. So, this will be equal to n into n minus 1 divided by 2 ok any doubt will know. See there is a mention of how you can arrive at Bohr's second postulate m v r equal to n h by 2 pi assuming electron is of deep overview wave we have done this when we studied the dual nature ok it goes like this. This is suppose electron orbit this is the electron orbit and if electron is a wave it will travel like a wave like this it travel in a way that here it will join in phase ok. So, basically the total path should be what in diesel times wavelength why because you can check from here to here 1 wavelength from there till here another wavelength from here till here 1 more wavelength from here to here 1 more fine. So, it can count number of wavelengths. So, if it has to merge here exactly in phase the total path should be in diesel times wavelength otherwise it will not be in sync with previous movement fine. So, total path is what 2 pi r this should be equal to n into lambda fine and what is lambda according to deep overview h by p which is linear momentum will become n v. So, you can get n v r is equal to n h by 2 pi. So, what D Boogley has done that coincides with the Bohr model. Now, see the theory in this chapter is very limited. So, we are done with the theory let us see a few questions that can be asked from this particular chapter. We will first touch upon the NCRT questions because that is how it should start. So, now the questions will be on entire chapter wherever what are you doing? Phone is the most precious thing nowadays you should not lose your phone everything is in the phone all the private conversation and everything your bank password. Yeah of course few games which you play all day you play games on phone. Okay anyways energy in the ground state for a hydrogen atoms electron is minus 13.6 electron volt. What is the kinetic and potential energy in this ground state? Kinetic energy and potential energy. How many are there? I am sorry how much? Done. How much is the kinetic energy? 13.6. 13.6. How much is the potential energy? Half of this. Half of this. So, when you add kinetic energy potential energy it should come out to be this or not. Is it coming? Potential energy is double of this. Kinetic energy is minus of this. We have done this. See you are facing trouble because you are not able to accept that okay energy is negative. This is negative if you double it it decreases it goes down. Okay next question hydrogen atom which is initially at the ground state as in at n equal to 1 it is okay it jumps to n equal to 4. Find out see why it will jump because it absorbs photon right you have to find out wavelength and frequency of photon. If you do it those who are watching it online and here is from Centrum Academy we are located in Bangalore and if you want to get in touch with us this is the phone number. You guys are stuck see this you can take it like this 1 by lambda is 1.097 10 is 7 into 1 by 1 which is square? 1 square minus 1 by 4 square which is 16 okay. Once you simplify this you will get the value of lambda. How do you get frequency? Multiply this with speed of light C by lambda. So, first it is easy to get frequency you know just multiply with C that is the frequency okay. The frequency which is C by lambda is 3 into 10 is power 8 1.097 10 is power 7 into 15 by 16. So, you will be able to get the frequency from here okay. Any doubt on this? See it is all about calculation many a times in physics. So, you have to be very very good with numbers and having good with number is an art. Do not think that it is donkey's work it is not something which is respectful. It is probably the most respectful thing among mathematicians being good with numbers. And some of the highest paying jobs they only get it practice lot of calculations.