 Hi, I'm Zor. Welcome to a new Zor education. Today we will continue talking about how molecules are formed from different atoms. Primarily it will be a few examples and a couple of principles on which this bonding is based. So today's lecture is called balance electrons. So this lecture is part of the course. The course is called Physics for Teens. It's presented on Unizor.com. I do suggest you to watch this lecture from the website because the lecture has textual description next to it on the website. So if you go to menu, you choose the Physics for Teens course, then the part which this lecture belongs to is atoms. And within it you will have basically a few different topics including the one which basically explains how the combination of atoms makes a molecule. And the lecture is part of this topic. So we did talk about different shells of electrons around the nucleus. And we did talk that chemical reactions involve only electrons and primarily the outer shells. Because the further electron from the nucleus, well, the easier it is to kind of combine with some other atoms, it's easier to move around, so to speak. Obviously this is a model. This is our model of how atom is basically constructed. But again, we do have experiments which kind of confirm this model to a very high degree of precision. So we accept this model and based on this model, again as you know from the previous lectures, electrons are positioned around the nucleus in shells and shells are subdivided into sub shells. Now, if you don't really know what I'm talking about, I suggest you to go back into the lecture on the same course, obviously, where I explain how the electrons are structured around the nucleus, including energy levels. Because I definitely will be using in this lecture all this material. So I accept that we know about shells and subshells. We know about number of electrons per subshell. And we know that there are certain names of these subshells. So I will use it. I assume that you know about it. Now, the next thing is that for some reason, and it's all based on quantum theory, etc., atoms would behave more, I would say, stable if their shells and subshells are complete. So as we know, every shell has a certain number of subshells. The first shell has one subshell. The second shell has two subshells. The third has three, etc. And every subshell has a certain number of electrons. Two, six, ten, fourteen, etc., with a step of four. So these are maximum number of electrons. Now, the subshells are filled up in the level of increasing energy. Potential energy is negative. So increasing means less, by absolute value, being negative, closer to zero. Zero is infinity. So the further we are, the greater the possibility of these electrons to fly away. But at the same time, atoms are more stable when their shells and subshells are completed, are filled to their maximum. So, for example, hydrogen has only one electron in the first subshell of the first shell, whereas the maximum is supposed to be two. Now, the helium has two electrons, which means completely filled up the first shell and first subshell. So the helium is, basically, inert gas. It doesn't react chemically, not easily react chemically with other elements, while hydrogen very easily combines with oxygen and gives H2O, which is water. So, again, atoms are trying to complete their shells to be more chemically stable. So if the shell is complete, they are not easily react with some other elements. And the example is all the inert gases, like helium, neon, xenon, etc. Okay, so based on this, we can state the following. So why different atoms can chemically react with each other, making a molecule? Well, that happens when, in some way, let's talk about two elements. These two elements complement each other as far as their number of electrons in shells and subshells. For example, if one particular element has only one electron on the outer subshell, and another element has one electron less than the maximum, they complement each other. So the electron can move to that element, and now this becomes positive, this becomes negative, and they stick to each other. That's just an example, or another example. For instance, again, something like two electrons are like extra on the top level shell, and two electrons are missing. Well, maybe these electrons can, outer shell electrons can combine together, and being basically a common property of both elements, and they fill basically this and that subshell, because they are shared, so to speak. Again, I'm not talking about how physically this mechanism of sharing is actually going on, but it's just a model, if you wish, and the model works. Now, this lecture will be probably about certain examples, rather than theory. Theory is, again, it's kind of deep, it goes to quantum theory, etc., which is completely beyond the level of this course. So, certain things you just have to take as axiom, like, for instance, shells and subshells, the number of subshells per shell, the number of electrons per subshell, etc. If I will talk about this, I just assume it as a given, without any kind of going into a theory why the first subshell of the first shell has two electrons. I'm not going into this. So, I'm taking it as granted, and I will talk about few examples to basically explain on example what exactly is happening. Okay, so my first example, which, by the way, we did talk about this before, I have sodium, and I have chlorine. Okay, now, the sodium has, this is electron configuration of sodium. I will write it first, and then I will explain what exactly I mean. Now, what is this? This is the first shell. It has only one subshell, the first one, which is abbreviated as S, for historical reason. Now, the second shell, two and two, has two subshells, because the shell number N should have N subshells, okay? So, the second shell has two subshells, the first and the second. The first again is called S, the second is called P, for historical reason. Now, the number of electrons, first subshell two, and then four more, and four more, four more, etc. Now, the third subshell, the third subshell has only one first subshell, the first third shell has only one first subshell, and there is only one electron left, because the atomic number is 11. Two and two and six is 10, 10, 11. So, 11 electrons are distributed among three shells, two, eight and one. Now, what's complete, what's not complete? Well, the first shell is complete, it has only one subshell, and it's filled up to capacity. The second shell is complete, because it has two shells, and both are filled to capacity. This is maximum two, this is maximum six. Now, the third shell is incomplete. Well, first of all, in theory it can have up to three different subshells, but that's half of the problem. The most important problem, the top shell, which is shell S of the third shell, has only one electron, while its capacity is two. You see, two, two, and this is one. So, the capacity of this subshell is two, but it contains only one. Let's talk about chlorine. Chlorine has one S2, the same thing, two S2 and two P6. Next is three S2 and three P5. Here is, we have, in the beginning, we have similar situation. The first shell, the second shell, completely filled up, completely filled up. Now, the third shell, well, in theory the third shell should have three subshells, but we don't even have the third one, we have only first two. Which is okay. It's not a problem. Now, let's talk about subshells. The first subshell, again, is filled to capacity. The second subshell, P, you see, P is supposed to have six maximum, right? Now, we have only five. Now, the atomic number is 17. So, we're supposed to have 17 electrons. So, it's two and two, six and ten and five. Okay, 17, 17 electrons. So, what happens in this particular case? Well, this electron is kind of extraneous, if you wish. And this has one less than the maximum. You see, that's the pair. That's the match. It's a happy marriage, basically, between these two elements. Because this thing can give, this thing could take, and then both will be complete. This will not have the third shell at all, and the previous one are filled up. And this one will have the last, the topmost subshell filled up to six electrons. So, if one electron from here will migrate to here, there will be a nice bonding. Now, under what circumstances electrons can migrate? Well, usually, and again, I'm not talking about every individual case and every individual condition, but usually metals have electrons freer than, let's say, nonmetals. So, sodium is a metal, and the electrons on the outer shell are generally, well, kind of moving. They're not completely free, but to free them from the nucleus is easier in metals than, let's say, in nonmetals. So, this electron can migrate, and it does, because, again, atoms are striving to complete their subshells. And that's why this electron, which is kind of migrating, and this atom wants to complete its own, its topmost subshell, this electron goes here. As a result, what happens? Well, as a result, sodium becomes positively charged, right? One electron goes here, so it becomes positively charged, the atom of sodium, the atom of chlorine becomes negatively charged, because it has one electron more. You see, before, we had the same number of electrons as protons in the nucleus, and atom was neutral. If one electron is migrated, then this becomes positive, this becomes negative, because there is a number of protons, one more, and number of protons here, one less, the number of electrons. And there is a connection, electrostatic connection between them, because positive and negative are combined together, and that's how we have the sodium chloride, which is salt, basically, which we use as whole. So, that's an example of the kind of bonding between atoms, which is called electrovalent or ionic bonding. Why is it called ionic? Because positively or negatively charged atom, when it's losing or gaining an electron, is called ion. So, this bonding is called ionic, or sometimes electrovalent bonding. So, that's it with this example. This is an example of ionic bonding, and I will do something more in the same, couple of more examples of ionic bonding. Okay, next one is barium. This is 56, and I will have a lot of problems here. Anyway, I'm not going to put all these electrons, I will put only the top one. The top one is 6S2, which means the shell number 6, the first sub-shell, S is the first sub-shell, and it has two electrons. Now, and we use the same chlorine, which at the end has 3P5. The third sub-shell has 5 electrons. Now, this is a complete sub-shell, because the sub-shell, S, has supposed to be maximum two electrons, and they are. However, the sixth shell itself has only one sub-shell. And again, for certain reasons, if it's just one particular sub-shell in a shell, it's still vulnerable. And since it's vulnerable, it can actually give up these, because the attraction to this particular atom is really great, because this atom really wants to capture extra electrons. And considering the electrons on the sixth shell are really far away from the nucleus, there is a possibility that these two will combine. However, you see, there are two electrons here on this top level sub-shell. This one needs only one electron. So what happens? Well, what happens is the following. Barium is losing two electrons, but one is going to one atom of chlorine, and another goes to another atom of chlorine. So these two electrons are captured by two different atoms of chlorine, and that would be the chemical formula is barium or two. That means two atoms of chlorine to one atom of barium. So that's another example when this top level sub-shell is filled, but considering it's an S on the first sub-shell in the sixth shell, and it's relatively far from nucleus, it's still vulnerable to be captured by some active atom of chlorine in this case. Now, just as a definition, the electrons which are involved in this moving around are called valence electrons, and every element has certain characteristic which is called valency, which is number of valence electrons. So number of valence electrons is two, number of valence electrons is one. So that's why we have two links from ion of barium, and one link goes to each atom of chlorine, because chlorine has valency of one, and barium has valency of two. Now, let me make your life slightly more complicated. Now, again, this is ionic bonding, because electrons are really moving from one atom to another. Now, let me give another example. So things are getting a little bit more complex with every new example. Aluminum, 13 atomic, and oxygen, which is 8. So aluminum is 1S2, 2S2, that's not interesting, 2P6, that's the beginning, everything is fine. Now, the third one, S2, as it's supposed to be, 3P1. So, the third shell has two out of three sub-shells, but two is already fine. Now, this one is completely filled up, this one has one extra electron. I mean, it has one out of six, which means it's vulnerable considering aluminum is a metal. So the top level sub-shell has one electron, which can be captured. Now, the oxygen has 1S2, 2S2, and 2P4. So what do we have here? Now, this thing can hold up to six, right? The maximum is for P for the second sub-shell, it's six, it has only four. So it needs two more. Well, this one has one more, which implies that maybe we can have something like aluminum or aluminum. So one electron from here goes to atom of oxygen and one electron from another aluminum atom goes here. And that would make the level two complete with the P6, so the formula is aluminum 2O. Well, the problem is that it leaves, if I will take this electron, it leaves only one sub-shell in the top shell. And as before with barium, for example, you remember that if it's only one sub-shell, it's still vulnerable. So what I want to say is that these electrons are also vulnerable. It means it can be captured by some other atoms. Now, what if all three electrons are out? Well, three electrons, this needs only two. So the good combination would be O, aluminum, OO. So three electrons are lost from aluminum and two electrons go to this one. You see, two electrons from this and from this go to this and two electrons go to this. So each atom of oxygen receives two electrons and each atom of aluminum loses three electrons. So the formula would be aluminum 2O3. Now, apparently this which leaves the top sub-shell basically naked, even a complete but naked, not protected by other sub-shells, is much less stable chemical combination. Actually, there are some special conditions when it can happen. So in practical life, this thing practically never happens. This thing does happen. This is a normal kind of combination. That's actually how aluminum is mined, I mean mined, whatever. This is the combination which occurs in nature and from this we extract aluminum using some process, whatever the process is. So aluminum can actually be either single valence electrons or three valence. Three is more, not significantly more, often occurs in nature. As one valence electrons, it practically never happens except on special conditions. So this is a little bit more nuance in the theory of valency of different atoms. The oxygen, I have to tell you, is always, it always has valency of 2 because it needs exactly 2 to complete the shell and all its sub-shells. There is nothing left vulnerable or missing or something like this. It would be complete. With 2 electrons, the oxygen atom is complete. These are all examples of ionic bonding when electrons are actually moving from atom to atom. And the last one I would like to basically use as an example a different kind of bonding when, you see, ionic bonding is more often occurs when one of the elements is metal because metal has freer electrons on the outer shell. Now, let's talk about different things. We will talk about carbon monoxide. This is carbon monoxide formula. So it's one atom of carbon, one atom of oxygen. Well, we usually deal with carbon dioxide, which is CO2. That's what occurs in air basically, and it's involved in some chemical processes, etc. But sometimes if there is an insufficient amount of oxygen, this molecule is formed, which is actually very harmful for breathing. However, I'm not talking about harm. I'm talking about how this molecule is created because it's simpler than CO2. And on a simple example, it will manifest whatever I want to say. Now, the carbon has formula, the electrons 1S2, 2S2, 2P2. And its atomic number is 6. Oxygen atomic number is 8. We already covered that. So now the problem is this is not a metal. So it does not really leave from the second shell these two electrons to complete oxygen. It doesn't happen so easily. So how this molecule actually is arranged? Well, this is a different kind of bonding. So ionic bonding, which we were talking about before, is when electrons are actually moving. In this case, electrons do not move because carbon doesn't really let it go so easily. However, again under special conditions, whatever, the bonding is created by doing the following. And I think I better do it with a drawing. So this is nucleus of carbon. This is nucleus of oxygen. So the first shell has two electrons. No problem with that. The second shell has only the first sub-shell two electrons. And this one has two electrons. Now, the second sub-shell of the second shell, which is this one, it has two. And this one has four. So what happens, these six electrons, two from now, one, two, and one, two, three, four, these two and these four, they are somehow become a common property of both atoms, atom of carbon and atom of oxygen. How is arranged geometrically, I cannot say. But in any case, they are considered by both atoms as theirs. So carbon consider these six as its, which completes its second shell. And oxygen considers these six as its own, four of its own really, and two, which I kind of borrowed. So they are sharing the responsibility. It's a joint custody, if you wish, of these six electrons on the outer sub-shells. And that becomes, and that makes complete both atoms, and that's why they are bonded together. So the sharing mechanism of sharing these electrons, which are under joint custody, becomes the glue, which glues two atoms together. I'm using this kind of comparison with divorced parents, but there are still common children, which they have joint custody. And they're still kind of meeting. Parents are meeting. Given they're divorced, they're still meeting for, like, bringing up their children to pay for the school and whatever else. So this is another kind of bonding. It's called covalent bonding. So the first one is ionic, when electrons are physically moving from one atom to another. And the second one is covalent, and this is an example of covalent bonding. And I think that's all I wanted to talk about today. So it's all about how the molecules are combined from atoms. There are ionic or electrovalent bonding, and there is a covalent bonding. First one, we're transferring electrons from one atom to another. The second one is sharing, shared custody. Okay, that's it. I suggest you to read the notes for this lecture on Unisor.com. There are a couple of much better pictures than this one. Other than that, that's it. Thanks a lot and good luck.