 Hi, I'm Zor. Welcome to Unisor Education. We continue talking about atoms, and right now we will spend some time to talk about interaction between atoms. So, today's lecture is about chemical bonding between atoms. Now, this lecture is part of the course. The course is called Physics for Teens. It's presented on Unisor.com Totally free website without any advertisement. No need even to sign in unless you are engaged in some kind of supervisory education. The site is much more preferable as the source of these lectures than, let's say, if you find it on YouTube, because on YouTube you have like separate lectures, basically. That's where they are stored. But the Unisor.com presents a course, which means there is a menu. Every lecture has textual explanation. And there are exams, which you can take as many times as you want until you get the perfect score, obviously. And then, as I mentioned, there are certain other functionalities like supervisory education, if you wish to get engaged in it. Okay, so let's get back to chemical bonding. First of all, when we are talking about chemical bonding between atoms, we are talking primarily about interaction, which does not affect nucleus of the atoms. So, nucleus is completely unchanged during these combinations. So, the combinations are available on the level of electrons. So, interaction between atoms as far as chemical bonding is concerned is interaction between their electrons, how they are rearranging themselves to create this bonding. Okay, now, there are certain elements which can bond together, certain simple elements under certain circumstances. And there are complex combinations, the molecules which actually interact as well. Now, I will use one particular example in this lecture, which is the combination of two different atoms, primarily the sodium and chlorine. Yeah, chlorine, which combined together give you sodium chloride, which is actually a regular salt, which we are using in food. So, this is atom, and this is atom. They combine together and get a molecule of salt or sodium chloride, if you wish. So, we will examine primarily this particular type of combination in details, so you will have a feeling about how atoms interact with each other. Now, prior to that, I would like to talk about certain cases when atoms do not want to interact with each other. So, there are certain atoms which basically are very difficult, possible but under very extreme circumstances. Generally speaking they are not willing to get into any kind of chemical bonding with anything else. As examples, we will consider so-called noble gases. Now, the first noble gas is helium. And to explain how basically, why is it not really willing to get into chemical bonding with anything else, we have to go back to the electron structure within the atom of helium. So, we go back to something which we have already learned in the previous lectures. Remember, the electrons are surrounding the nucleus. They are basically organized in shells and shells are numbered like one, two, three, etc. Now, each shell has a certain number of sub-shells. The number of sub-shells corresponds to the shell number. So, shell number three has three sub-shells. Shell number one has one sub-shell. And sub-shells are also numbered one, two, three, four, five. However, for historical reason, people are using letters. And the first one is S. The second one is P. The third one is D. And I'm not going to go any further. We already did this. And under the circumstances which we will study, we don't actually need more than three sub-shells. So, the first shell has only one. The second has two. So, I can actually wipe out this. The third shell has three sub-shells, etc. Now, how many electrons are per shell? If you remember, there is a formula. For M is one of those numbers. So, S has two. One times four minus two. P sub-shell has six. And D sub-shell has ten electrons. So, this is electron structure of atom in general. And as far as Hellen is concerned, it has only two electrons in the first shell. So, the first shell is complete. So, it has two electrons. First shell S sub-shell, which is the first one. And it has two electrons. Now, there are no more sub-shells in this shell. And there is no more electrons which can fit into this sub-shell. So, we have one shell, one sub-shell, which is complete. There is no more room for anything else. Because to push something in, some electron in, which is not really easy, you have to really create a new sub-shell. Which is always difficult for whatever reasons. Okay, great. Next. Next, noble gas is neon. Which we are using like everywhere in neon lighting. Now, what is the electron structure of neon? Okay. First of all, it has ten different electrons and they are divided into layers like this. So, the first shell can have only one sub-shell and it's completely filled up. Now, the second shell can have two different sub-shells, S and P. So, S it has only two again. S shell always has two. And on the second shell, the P sub-shell, it has 0, 6. 2 plus 2 plus 6 is 10. It's 10 electrons. So, this has 2, this has 10. Now, again, the same situation. This shell has only one sub-shell and it's filled up. It cannot hold, S cannot hold more than 2. Now, the second sub-shell it has, the second shell has two sub-shells, S and P. S has no more than 2 and it's filled up. And the P's can have 6. It's also filled up. So, what we have here is exactly the same situation. All the sub-shells are complete. To introduce something more we need to create a shell or to take electrons from it, which means that we will kind of work against the desire to be complete. So, Atom's desire to be complete, if you wish you can just formulate it this way, they are tending to be complete if possible. So, but this one is already complete. So, it does not really need any pairing with anybody to borrow electrons to complete its shells. So, that's why these are inert elements, these noble gases. Now, just for example, let's consider the next one. Next one is what? Argon. Argon is 18. And let me just write it straight through. The beginning is exactly the same. Now, we need 8 more. So, we have to start the new shell. The shell number 3 and it has S2 and P6. Again, we have started a new shell which can have up to 3 different sub-shells, but we don't need really 3rd one. 2 already sufficient. Both of them are filled up. S can have 2. P can have 6. They're filled up. And the total is 2 plus 2 plus 6, 10 and 18. So, everything is fine. Again, all the sub-shells are complete. They are filled to their capacity. And that's why it's inert gas. It's a noble gas. Just out of curiosity, one more. Krypton. Now, Krypton has 26, if I'm not mistaken, electrons. Now, the beginning is the same. So, I will put it here, like this. Argon. And then we have to add more. Actually, it's not 26. I skip. I think I skipped something. Because it has everything which has Argon plus it has 3d10 and 4s2 and 4s6. So, it has 18 more. So, it's 36. So, that's what's very important here. Now, again, what we have. This is complete. 3g. Now, d can have this. So, we complete the 3rd shell. And then we have to start the 4th shell. And again, the first and the second subshells, s and p. That's supposed to be p, are filled to their capacity. s to the 2 and p to the 6. And we have 36 electrons. Same situation, again and again and again. All these inert gases have complete subshells filled to the max. And that's what makes them unwilling to go into any combinations. Now, obviously, the next thing I would say, okay, those elements which do not have a complete structure of the top subshell, we're talking about usually the top subshell which is not filled up to capacity. So, all those elements are more willing to get into combinations. That will bring us to sodium chlorine. Okay, so let me just wipe out this. So, we know why noble gases are noble. Okay, so let's talk about sodium. Sodium has combination of 11 electrons. And let's start. The first subshell is complete. Now, the second shell has two subshells. Again p, s and p. 6. How many do I have? 2, 2, 6, 10. So, we start the third shell and we have, obviously, the only one electron. So, the third shell, the first subshell s, can have two. Now, we have one. So, what do we do to complete it? Well, either it should give one electron or it should take how many for s, or take another electron. Yes, that's where it is. It's supposed to be. Okay, now let's talk about chlorine. Now, chlorine is 17, if I'm not mistaken. Yes, 1 is 2. 2 is 2. 2 p, 6. Now, 3. We have to fill it up. I mean, s2. The first subshell. 3, 2, 6, 12. 5 more. Okay. The next one can have up to 6. But we have only 5. We have one less. And here, we have the most important things. You see, this thing can give up one electron to be complete. This thing needs one electron to be complete. Now, the desire to be complete is very, very strong. I don't know why. And what happens in this case, they are sharing the electrons and basically one electron comes from here to here. And what happens is the following. Sodium is kind of transforming itself into so-called sodium positive ion and give up negative electron. This electron is consumed by chlorine. It goes to this particular subshell. Well, not goes to. I mean, I don't know exactly how it happens. But somehow it happens that it goes into the sphere of influence, if you wish, of another nucleus. So, on the level which we are in right now, you can just, you know, consider this electron really kind of changes the place, although it's not exactly this. And what makes it is chlorine negative ion. So far all we have done is the electron goes from sodium to chlorine. Now, because electron is negative, whatever is left is positive ion of sodium. And when this electron is accepted by atom of chlorine into the topmost subshell, the atom becomes negatively charged basically. Now, what happens with positive and negative charges? Well, they attract. So positive ion plus negative ion attract together and that's what makes a molecule of salt. And because these are oppositely charged, electrically charged atoms, they stick together and that's what makes the molecule. So, the molecule is kept together by basically electrostatic forces, if you wish. Something like this. So, it's no longer the same atom of sodium and the same I should say sodium, sodium is later name. The same atom of sodium as it was before and this is not exactly the same atom of chlorine as it was because this guy lost an electron for the benefits of this guy. So, they are ions now. Ion is basically an atom which either gained or lost electrons, some electrons, one, two, whatever. So, that's what happened actually in this particular case and that's what makes the molecule. Now as a result of all these kind of manipulation with electrons, what I would like you actually to have like a final thought that the atoms themselves contain nucleus and electrons. Nucleus does not participate in bonding. Only electrons are rearranging somehow and this is an example. Now, there are more complicated examples which I don't want to go into because it's not the purpose. This is something like a chemistry course or whatever but from the physical aspects I would like you to understand that this exchange of electrons is at the heart of chemical bonding. Now, I have summarized whatever I was talking about in a few different rules if you wish and I'll just present it to you. Number one atoms like to be complete in the terms of their shells and sub-shells. So, again, why it's difficult for me to say it might be related to some deeper quantum properties, I don't know, but atoms like to have complete sub-shells and complete in these terms. So, every sub-shell by number, the first, the second, the third, has a certain number of electrons which make this particular sub-shell complete and that can be actually theoretically founded in some quantum mechanics. Now, since they do their, well, I should say desire or need to be complete is very, very strong. So, if there is a possibility for finding a pair which is also willing to complete, but differently, one atom is willing to complete by, willing to complete its sub-shell structure by, let's say, giving a certain number of atoms and if another atom at the same time is willing to accept these few electrons to make this complete so they should really kind of match to each other, you see. One electron is extra here. If we take it away, we will have a complete picture and one electron is needed here. So, one can be lost and one can be accepted and both will become complete. So, this is a pair. It's a suitable combination of atoms. So, if such a suitable combination exists when one becomes positive ion and another becomes negative ion, then there is a possibility for their chemical bonding into molecule. So, that's basically the rule. So, again, and by the way, it's not easy to part with an electron here. It's easier to accept. Why? Because the electrons are actually attracted by nucleus. So, we have to somehow rip it off from the nucleus. But again, the desire to be complete is probably stronger than the attraction of the nucleus and that's why an electron can leave this one and go here. Now, why is it not the other way around? Why not these five to go here to make this negative ion and this is positive? Well, probably because it's much more difficult to rip off five electrons from here than one electron from here. So, this is more natural kind of transformation. So, the electron from one to five, not five to one. Okay? Next. So, what we need is we need a proper effect between two different atoms to become chemically bonded. And what's also interesting is that it's like a marriage, if you wish. In some way, the relationship between these two components of the molecule, now in this case it's a simple molecule, they do actually behave like a happy marriage. When people complement each other, right, here is also this electron complements this. And that's why we have such a strong bondage and very stable molecule, in this case a molecule of salt. And what also I can say is that there are much more complicated molecules. But again, their principle of connecting of different atoms is exactly the same. So, one atom is hooked to another based on certain electrostatic forces. And then that one might be connected to another and another and we can have a structural formula of a molecule where atoms are connected to each other. But this is basically a course of chemistry which I don't want to go into. But if you do study chemistry, you will definitely be dealing with these structural formulas of molecules where you really see how different atoms are hooked to each other based on these type of connections. Okay, that's it for today. I suggest you to read the notes for this lecture, so go to Unisor.com. The course is called Physics for Teens. The part of the course is atoms. And when you open the menu it would be a chapter called Interaction of Atoms. Within that chapter this is the first lecture. Okay, thanks very much and good luck.