 Let's explain how ionic molecules are formed. To do that, we need to look at the electronic configuration of noble gases. Here's what I mean. If you take helium, we know that it has two electrons in it. But how are they arranged inside the atom? Well, it turns out that the two electrons of the helium are in the first shell, which we call the K-shell. Alright, and that's it. But what if you consider neon, the next noble gas? It has 10 electrons. How is that arranged? Well, again, the first shell contains the two electrons because that's the maximum capacity of the first shell. But then if you go to the second shell, which is the L-shell, the second shell has a capacity to have eight electrons. And so in neon, you have the first two in the first shell, the K-shell, and the next eight in the next shell. And that's how you have two and eight. That's the electronic configuration of neon. Okay, let's do one more. What about argon, which has 18 electrons? Just like before, just like with the neon, we start with the two in the first shell, then the eight in the next shell, and the remaining eight will come in the next shell again. What we will find if we continue this with all the other noble gases is that except helium, all the noble gases will have eight electrons in its outer most shell. And so we thought that, okay, maybe this is the reason why these gases are noble, meaning they don't react. Maybe the rule for not reacting, the rule for stability, which we now call as the octet rule, is that you need eight valence electrons. Valence means electrons in the last shell, the valence shell. If you have eight valence electrons, you get stability, and then you will not react with anything. How does this help, you may ask? This helps us understand how other atoms are going to react, because their motivation is to achieve octet. Let's see how. So let's consider the formation of NaCl. For that, let's look at the electronic configuration of sodium. Sodium has 11 electrons. So how will it, how will it be arranged inside the atom? Well, again, the first two in the first shell, the next eight in the second shell. So we have 10 now, and we have only one remaining. So remember, the second shell can only accommodate maximum eight. So where does the remaining one go? It has to go in the third shell. So now, if we were sodium, how could we achieve octet? Well, one way is to get seven more electrons, so that the final one, this third shell, also has eight electrons, but that's so hard to get seven more electrons. Instead, if we were sodium, we would want to just lose that one electron, because if we lost that one electron, then we will have octet, and we will go back like this if we lost that one electron, and we would be stable. So as sodium, we want to get rid of that one electron so that we get our octet, okay? So that's the sodium story. But what about chlorine? Chlorine has 17 electrons. So what would its electronic configuration look like? I want you to pause the video at this point and see if you can write that down yourself. All right, let's go. So again, we start with the first two in the first shell, then we get the next eight. So we are done with 10. Now we have the remaining seven. That remaining seven comes in the last shell. And now if we were chlorine, how would we achieve octet? We could either get rid of all the seven electrons so that we have octet here. The fancy shell has eight electrons, but that's so hard to get rid of all seven electrons. Instead, if we got one more, if we, if we, if somebody gave us one more electron, then we would finish the octet of the third shell and we would then be stable. So look what has happening. Sodium wants to get rid of its electron to achieve stability. Chlorine wants to gain one electron to achieve stability. That's such a cool deal. So that when sodium and chloride come together and the conditions are right, sodium will transfer one electron to chlorine, sodium becomes happy, chlorine becomes happy and everyone is just happy now. But notice what has happened. If sodium loses that one electron, it becomes positively charged. And if chlorine gains an electron, it becomes negatively charged. And so now these have become ions and positives and negatives attract. And because of that, they're going to stick to each other. And this is how ionic bonds are formed. Beautiful, isn't it? Now because drawing this and writing this is such a pain, if you're doing this in pen and paper, what is a faster way to represent that? A faster, quicker way to represent is using an electron dot structure. And so the way we represent this in electron dot structure is we write like this. We show the valence electron of the sodium that is over here. We show the valence electrons of chlorine, the seven valence electrons of chlorine. And we show the transfer from sodium to chlorine. To differentiate the two, we use dot for one, we use cross for the other. Same dot structure that we've been using earlier as well. And now when this happens, what do we get? Well, sodium becomes positively charged. Chlorine gets that extra electron becomes negatively charged and they stick to each other. And this is how we show. Usually the positive charge we show in say ground brackets, the negative charge species we show in a square bracket and then we put them each other showing that they are now bonded. This is how sodium chloride is formed. Okay, let's do one more. Let's consider magnesium chloride. How is that formed? Well, again, let's look at magnesium. It has 12 electrons. Why don't you pause the video? And see if you can figure the whole thing out yourself. All right, let's do this. Electronic configuration for magnesium, the first two in the first shell, the next eight in the second shell. So we are done with 10. We have two more remaining. The two more has to be in the last shell. Now as magnesium, we would say, ah, I want to get rid of these two. If I got rid of these two, I would go back to being, having eight electrons octet and I would be so happy. So as magnesium, we want to get rid of these two electrons. Okay, what about chlorine? We've already seen what happens with chlorine. It has 70 electrons, two in the first, remaining eight in the second. So that's 10. And the last remaining seven is in the last one and it wants one electron. So look at the situation that we have this time. Magnesium wants to get rid of two electrons, but chlorine only wants one electron to complete its octet. So how do they, how are they going to arrange it? Well magnesium says, look, I'm going to give you this electron. And if there's another chlorine nearby, I'm going to give the second electron to the another chlorine. And this is how a magnesium says, you know what? I'm going to bond with two chlorine. I'm going to transfer my electrons to two chlorines and that's how, that's how it's going to work out. And therefore magnesium bonds with two chlorine and that's why you get MgCl2. It all makes sense now, isn't it? So again, how do we write the electron dot structure? Well, same thing as before. These are the two valence electrons of magnesium, which we are transferring to chlorine. And look, chlorine has seven valence electrons, whatever we have over here. So what do we get as a result of this? Well, look, magnesium has lost two of its electrons. So it'll have two positive charge, so two plus chlorine. Each chlorine has gotten only one electron. So each chlorine has one negative charge. But since there are two chlorines, there are two chlorines that is represented over here. So two such chlorines together bonded with one magnesium and the charge keeps them together and ionic bond is formed. That's how we get MgCl2. So that's basically how ionic bonds are formed. Beautiful, isn't it?