 Next observation is binding energy, when I am adding EBN, I mean binding energy per nucleon. So effectively I am talking about binding energy which is there for each particle inside the nucleus. So EBN is lower, it is lower for both, mass number less than 30 and mass number greater than 170. Getting it, now these are the two critical observations that are made from the graph. If binding energy is less, what I can say if binding energy per nucleon is less, the nucleus is relatively more stable or less stable, less stable, fine. So more is the binding energy, it means that more was the exothermic reaction when nucleus got formed, fine. So here we can say that the nucleus whose mass number is less than 30 and nucleus whose mass number is greater than 170, both are relatively less stable, okay. So what they will try to do, like every object in this universe, they will try to move towards the more stable configuration, okay. So hydrogen, lithium, beryllium, all these nucleus will try to combine and will move towards higher binding energy, that is they will move towards iron nucleus. And in order to go towards the higher mass number, they need to fuse together, they need to combine, okay, they need to increase their atomic mass number, fine. So the lesser atomic number one, the reaction that is favorable there for nucleus is nuclear fusion reaction. Nucleus will get fused and there will be two nucleus, two nucleus will combine to give a single nucleus like that. But for mass number greater than 170 and if they want to become more stable, they need to decrease their mass number, getting it. So they will split and fusion reaction that is what it is called, okay. So higher mass number nucleus, fusion is more favorable and lesser mass number nucleus fusion is more favorable, okay. Although there is a huge activation energy that is present for any of these reactions fusion or fusion. Both of the reaction, you need to have very, very high activation energy, all right. So they won't happen just like that. So we will now talk about some of the conclusions that we can draw from these observations, okay, write down. Now first of all, we have already touched upon these things that now since we are talking about conclusions, we can start from one. We can say that we are talking about binding energy which is very high, mega electron volt, okay. So these kind of binding energy will come only when there is a very, very strong bond that is present. Do you have any idea what is the bond energy when we talk about a typical covalent bond? How many electron volt that is, okay. So the hydrogen bond that is formed in the water molecule has 0.24 electron volt, the binding energy, okay. Now in terms of kilojoule per mole it is given, okay. So when you talk about typical covalent bond, there in chemistry you have always calculated in terms of the moles, right. So if you divide it with number of moles, for example, the, let us say 100 kilojoule per mole is the bond energy, okay, 100 kilojoule per mole. This is one of the bond energy. So one bond has how much energy, 10 or 100 into 10 raise to power 3 divided by Avogadro number per mole it is, right. So for one bond it is 6.023 into 10 raise to power 23, okay. So this will come out to be around what, 1 divided by 6 into, this is 10 raise to power 5 so it will be 10 raise to power minus 18, okay. So it will be 10 divided by 6 into 10 raise to power minus 19 and in terms of electron volt if you have tried to find out it will be this divided by 1.6 10 raise to power minus 19. So we are talking about few electron volt for covalent bonds. Are you guys with me now on this? Yes sir. But when it comes to the thing which is inside the nucleus it is tremendous, it's like, you know, one million times more is the energy which is required to break the nucleus or nuclear bonds let us say, fine. So tremendous amount of, you know, there has to be some sort of mysterious force that is present to create such strong bond because had it been just electrostatic force then even the covalent or ionic bond is electrostatic force. So that will just create few electron volt energy bond but we are talking about mega electron volt. So there has to be some other force, electrostatic force is not sufficient to create this. So this force is called nuclear force which is very, very strong compared to the normal electrostatic force. It's like comparing gravitational force with electrostatic force. Similarly, when we talk about nuclear force, nuclear force is million, million times stronger than the electrostatic force, fine. So the conclusion that we can draw here is there has to be some sort of attractive force that is present inside the nucleus and that force we are saying nuclear force, right down. So there is a presence of a nuclear force to create binding energy of mega electron volt per nucleon. There should be a nuclear force. The presence of nuclear force can be concluded from these observations. Now, the binding energy per nucleon is constant from 30 to 170. What does it mean? If you take a neutron, let us say neutron. Neutron is let us say surrounded by neutrons and protons. So there will be only fixed number of protons or neutrons that can be very close to one neutron. Yes or no? Suppose a nucleus has 100 proton and it has 70 neutron, but the one neutron or one proton will only have fixed number of particles which are closest to it. Yes or no? It does not matter what is the total number of protons or neutrons inside the nucleus because there is no sufficient space. Are you getting it? Yes sir. Yes sir. It is like this, you know, you take a ball, so there will be only fixed number of balls that can completely surround a single ball, no matter how many balls you have. You cannot keep on surrounding it by infinite number of balls, okay. So, you know, you can say that the bonds that are getting created because of the nuclear force, okay, they are very short range, they are very short range. If the particles are very close, then only these bonds will get formed, okay. So now you can understand that if you increase number of particle inside the nucleus, then also binding energy per nucleon is not increasing because neutron can form only fixed number of nuclear bonds or proton can also form a fixed number of nuclear bonds because nuclear force is very short range. So the particle have to be literally, you know, surrounding it and that cannot go beyond a certain number even though the nucleus may have lot of particles in it. Are you getting it? So we can understand it like this, so write down this observation, you can conclude second point that the nuclear force is a short range force, it's a short range force and it has to be attractive also. It is attractive between proton-proton, it is attractive between neutron-neutron or neutron-proton. It doesn't matter what is the charge, it is independent of the charge, okay, okay. Now tell me why binding energy goes down for mass number which is greater than 170, why binding energy decreases? Just think over it, what is the reason for it? Now see when the mass number increases, the radius of nucleus increases, right, radius of nucleus we have already learned is r is equal to r0, a to the power 1 by 3. So when you increase the radius of the nucleus, the particles inside the nucleus they spread across, okay, because of that since nuclear force is a very short range force, lot of particles they will not be able to form a very strong bonds because the distance between two nucleons will increase, that will destabilize the nucleus, are you getting it? Yes sir. Fine, similarly when the atomic number is very less they will not be sufficient number of nuclear bonds that can be formed by proton or neutron because of that the binding energy again goes down and it remain constant between 30 and 170. So these are the some very important conclusions that can be derived from this graph, okay. Any doubt with respect to binding energy? Now we are moving to next topic. Any doubts? No sir. Okay, by the way, whenever you are answering your questions in the school, don't use the term nuclear bonds, okay. I just created that so that I could explain you in a better manner, you just talk about it as if it is not a bond it is force, nuclear force, okay, whenever you write some theoretical explanation.