 Now we'll see what is intermolecular forces and what are the different types we have? Intermolecular forces. So theoretical just to know the definitions and all that is it, nothing much. So intermolecular forces are generally very weak forces. OK. And total we have four types of intermolecular forces. Right. So there are, write down, there are four types of intermolecular forces known. There are four types of intermolecular forces, intermolecular forces known in the neutral molecules, neutral molecules. OK. These four types are, first of all, you write down the name. First we have dipole-dipole interaction. Dipole-dipole interaction. The second one we have dipole and induced dipole. Dipole and induced dipole interaction. One second, guys. Yeah. Dipole-dipole interaction, dipole-induced dipole interaction. And the third type we have, that is London dispersion forces, London dispersion forces. And the last one is hydrogen bonding, which we had already discussed. Correct. So these are the four types of intermolecular forces we have. So we'll discuss this one by one. See, dipole-dipole interaction means what? Let me just explain you first what is a dipole. OK. Dipole means what we have, you know, two poles here. One is supposed positive charge, so otherwise negatively charged, right? OK. So this we call it as a dipole. You have a rod. One side of the rod, suppose positive charge is there, and another side is negative charge. Small length. Length should not be too big. OK. So this rod, then it behaves as a dipole because there's two poles, correct? So if any electric field is there, so this electric field, if it acts on this charge in this direction, so on the positive charge, it will be in opposite direction, right? So in presence of an electric field, it has a tendency to rotate like this because of force acting in the opposite direction. Torque basically happens over here. So all these things are not required here in chemistry. These things you will study in physics. OK. But this is what the dipole is. Two poles we have there at the two end. One side we have positive charge, one pole. Other side negative charge, another pole, right? In chemistry, what happens when you talk about the dipole? So we have, suppose, a molecule, correct? Like, for example, if I talk about this NH3, OK? Or I'll take the NH3. NH3 will have, right? So how do we think of a dipole in a molecule like this? OK. So dipole in a molecule like this we can understand because the electronegativity difference between the atoms which are bonded. Like you see, nitrogen is highly electronegative. So it is delta negative, delta positive, delta positive, and delta positive. Each bond here, it is behaving as a dipole because, again, the length is small and positive negative charge at the two end, right? So it is behaving as a dipole here, correct? And that is what the meaning of dipole-dipole interaction we have. It is basically exist in polar molecules. Because of this electronegativity difference, the mu of this, the dipole moment, is not equals to 0, right? And hence, it is polar molecule. If dipole moment is 0, then the molecule is said to be non-polar, correct? So dipole-dipole interaction, like I said, it is possible in two polar molecules, OK? I'll just take this separately also. Let me just two points, if we just write down here, two polar molecules. It exists between polar and polar molecules. When we talk about dipole and induced dipole, so induced dipole means because of one of the dipole, that one dipole has been induced or introduced into the another molecule. So this is for dipoles with polar molecule and induced dipole is with non-polar molecule. So when a polar molecule comes closer to a non-polar molecule, then this negative charge, OK, also attracts this towards the side. The electron pair will be on the other side. So this was non-polar. But when it comes closer to a polar molecule, this also induced some charge into this. And hence, it is acting as an instant dipole, we say. An instant dipole creates in this neutral molecule, which was non-polar initially, right? So this kind of dipole-dipole interaction that we have, we call it as dipole-induced dipole interaction. So basically, dipole-induced dipole interaction is possible in one molecule, which is polar, other one other molecule is non-polar, correct? Let's discuss this one by one. Had in morning, we're not going to discuss because we have done this already in chemical morning chapter. Let's discuss these three one by one. So write down the first point, dipole-dipole interaction. Dipole-dipole interaction. Write down this force exists between two polar molecules. In short, I'll write down here. Between two polar molecules into polar molecules, it is weaker than ion dipole forces and effective when polar molecules are very close. It increases with the molecular size dipole moment. If molecular size is more, molecular weight is also more, correct? So sometimes we also say molecular weight. So molecular size and dipole moment we have. More dipole moment, more will be the interaction because the two bonds, you see this, the two bonds are close enough, positive, negative. And one more we have here, negative, positive, positive, negative. So this is the interaction we have between the opposite charge. This interaction is dipole-dipole interaction we have. So for this, dipole-dipole, the two molecule must be polar. Then only we have charge separation like this. The second one you write down. The second one we have dipole-induced dipole. Induced dipole. Next, see dipole-induced dipole. For dipole-induced dipole, it is possible between a polar molecule and a non-polar molecule. Polar and non-polar molecule. If you look at this molecule, which is polar, so it has positive and negative charge like this dipole. If the another molecule comes, which is non-polar, comes closer to this, then this positive charge will attract the electron. So this electron will come closer to this side because the positive charge is attracting electron. And another side, this side becomes relatively positive. So this side of dipole creates into this. This we call it as induced dipole. You keep it away. You remove this particle from this point. Other side, right. This dipole won't be there. Again, you come closer to this. We'll have a dipole, closer to this molecule. So this molecule we call it as here. It is an induced dipole. Induced dipole interaction. That is induced dipole. This is dipole and induced dipole interaction. We have polar and non-polar molecules. This kind of forces, we also call it as Debye forces. Dipole-induced dipole. We also call it as Debye forces. This is also very weak. Even it is weaker than dipole-dipole forces. Next, it increases with first one, the dipole moment of polar molecule. Dipole moment of polar molecule. And second is polarizing power, polarizing power of non-polar molecule. It means how easily this non-polar molecule is generated. Polarizing power of non-polar molecule. It means how easily this non-polar molecule can polarize. Polarizing power of non-polar molecule. The third one is London dispersal forces. It exists between non-polar molecules. Two non-polar molecules. It is due to the random motion of electrons in one atom of one atom, an instant dipole creates in the second atom, which influences the motion of electron in another molecule or atom. It is mainly for noble gases. For example, if I take the example of helium, this is the helium molecule we have. Helium has two electrons. For any instant, two electrons are residing on this side. This side will be delta negative partially and this side will be delta positive. This positive charge creates a dipole here. This positive charge will attract this electron towards this side. These electrons will be here then, delta negative and delta positive. Both molecules, you can say, the dipole is being induced here in both the molecules. It is not like that this will be there always. It is because of the motion of the electron. The electron is continuously moving. For any fraction of a second, or for any fraction we can say, you cannot even imagine the time over here because position of electron we cannot define. But for example, or for any instant, if the two electrons resides here, for suppose one-tenth of a fraction of a second, for that time also if the electron resides this part, this side here, then this side becomes partial negative charge that is delta negative, so this side will be delta positive. Now at this moment, this positive charge will attract the electrons of the other molecule. Hence, it influences the motion of electrons in the other molecule. This attracts this electron towards this side and hence here also a dipole creates. This kind of force of attraction that we have here is London dispersion force. It will be there for, you know, you can say one by thousand times of a fraction of seconds. You cannot even imagine for how small, for how long, you know, time obviously because electron is continuously moving, right? It has wave property. So it will be very, you know, for a very small time, you cannot even imagine that time. Plus it is very weak also since the electron is continuously moving. So if you talk about the strength of these kind of, you know, intermolecular forces, all are weak forces, but among this, among all these, you know, intermolecular forces, dipole-dipole is the strongest one and then, you know, this one, dipole-induced dipole and then London dispersion forces, okay? London dispersion forces increases with, with first of all the number of electrons, if more number of electrons in the, than the strength will be more, number of electrons, molecular size and then polarizability is the three condition we have. Hydrogen bonding we have already done, so I'm not doing it here again. So this is the intermolecular forces we have, different types of intermolecular forces, right? Diffusion, diffusion we have done already. Yes.