 When sodium reacts with chlorine, we get sodium chloride or NaCl. But how are things happening at an atomic level? Well, that's exactly what we are going to find out in this video. We will learn how metals react with non-metals and what are ionic bonds and how are they formed. Well, before we start learning about these, we will have to remember a few things. First, how are electrons arranged in an atom? What is the electronic configuration of an atom? And second, what's so special about noble gases? Now you might be wondering, Ram, why noble gases? So see, noble gases are inert in nature. They do not take part in any chemical reaction. So we want to understand what makes them so special. Maybe from there we can understand why other elements want to react. So let's begin. So here I have taken neon, which is a noble gas. Its atomic number is 10. This means that neon will have 10 protons in its nucleus. And since this is a neutral atom of neon, it will also have 10 electrons going around the nucleus. Now see, these electrons, they will not be going around the nucleus in a random fashion. Instead, they will be going around in fixed regions called shell. Now there could be many shells, 1, 2, 3, 4. And we saw that these shells are given special names, KLMN. And if you are wondering why these weird names, then don't worry about them right now. There is some historical reason and we will talk about them in a future video. Let's now see how 10 electrons go around in these shells. So the first shell, the one that is the closest to the nucleus, also called the K shell. It has a maximum capacity of 2 electrons. That means only 2 electrons can be over here. Okay? So out of the 10 electrons, 2 occupy the K shell. Meaning 10 minus 2, we have 8 electrons remaining. Now the second shell or the L shell, it has a maximum capacity of 8 electrons. That means all the 8 electrons, they will occupy the L shell. So here we have 2 electrons in the K shell and 8 electrons in the L shell. And this is how the 10 electrons of neon go around its nucleus. So one thing to notice over here is that the outermost shell of neon, or the valence shell, outermost shell is also called as valence shell, has 8 electrons in it. Okay? Now with this, let's look at example of one more noble gas. Argan. Its atomic number is 18. Now this means that there will be 18 protons in the nucleus of argon. And since we have taken a neutral atom of argon, we will have 18 electrons going around the nucleus. Now let's see how these electrons go around in shells. So in the first shell or the K shell, we can have a maximum of 2 electrons. So there you go. In the second shell, you can have a maximum of 8 electrons. So so far we have 2 plus 8, 10 electrons, 18 minus 10 that leaves us with 8 electrons. Okay? So in the third shell, all our 8 electrons will be accommodated. And over here you can notice that even in argon's outermost shell or the valence shell, we have 8 electrons. In fact, all noble gases except helium have 8 electrons in their outermost shell. Now this made us think, is it because of this special arrangement of electrons that our noble gases are inert in nature? And yes, this came out to be somewhat true. We noticed that other elements were participating in reactions. They were losing, gaining or sharing electrons just to be able to attain 8 electrons in their valence shell or outermost shell. Now seeing this, we gave this phenomena a name. We call this octate rule. Now this states that generally elements will participate in reaction to attain 8 valence electrons. Now let's look at some examples of this. So here I have sodium and its atomic number is 11. That means sodium will have 11 protons in its nucleus and 11 electrons going around it. Now let's see how these electrons go around in shells. So in the first shell or the K shell, there can be a maximum of only 2 electrons. Now in the next shell, we can have maximum of 8 electrons. So so far we have 2 plus 8, 10 electrons but sodium has 11. That means one more electron is pending. This electron will go to the next shell. Here this is our 11th electron. So over here you can notice that sodium's outermost shell or the valence shell has only one electron. That means its octate is not complete. Now how can sodium complete its octate? Now one option is that sodium gains 7 more electrons. So 7 plus 1, 8 that means sodium's octate will be complete. Let's see this is not possible because see electrons go around the nucleus because they are attracted by the protons in the nucleus. But if you increase the number of electrons by a lot compared to the protons, they will not feel equal amount of attraction and that's why they will fly off. So that's why this is not a good option. What can happen is that sodium will lose the one electron in the valence shell. And now sodium's outermost shell will be this, the second shell, the L shell. And you can notice that this already has 8 electrons. So by losing one electron, sodium gets a complete octate. So when sodium participates in a reaction, it prefers to give away this extra electron to complete its octate. So sodium prefers to give one electron. Now let's look at chlorine. So chlorine's atomic number is 17, meaning it has 17 protons and 17 electrons going around it. Now let's see in which shell how many electrons are there. In the first shell, there could be a maximum of 2 electrons. In the second, we can have a maximum of 8. So we have 2 plus 8, 10 electrons, 17 minus 10, meaning 7 are remaining. So 7 electrons, they will occupy the outermost shell over here. So here also, chlorine's octate is not complete. Because in the outermost shell or in the valence shell, we have only 7 electrons. We need one more electron for chlorine's octate to be complete. So chlorine will need one electron, chlorine will accept one electron. So sodium and chlorine, they seem to be made for each other. Sodium wants to get rid of one electron and have a complete octate, whereas chlorine wants to accept one electron and have a complete octate. And that's exactly how they react. But see, there are a few more things that happen. Over here, sodium was a neutral atom in the starting. It had 11 protons and 11 electrons, equal number of positive and negative charges. But when sodium loses one electron, now sodium has 11 protons, but it has only 10 electrons left. That means sodium has one extra proton, meaning one extra positive charge. So over here, we now get sodium plus iron. Now since over here chlorine is getting an extra electron, chlorine will become chlorine minus iron. Chlorine will get a negative charge. And we also know that opposite charges, they attract each other. And that's why there will be a strong electrostatic attraction between Na plus and Cl minus ions. And because of this, both the ions stick together. And that's how we get NaCl. Now one last thing. The compounds that are formed in such a way are called ionic compounds. Due to the transfer of electrons between a metal and a non-metal, ions are getting formed. Positively charged ions and negatively charged ions. And these ions attract each other. And that's when the compound gets formed. So that's why these compounds are called ionic compounds. Now let's summarize the video. In this video, we saw that elements react to get a complete octate, meaning 8 electrons in their outer most shell, in their valence shell. Now when metals and non-metals react by transferring electron. One will lose electron and get positive charge. The other, without gains electron, will get negative charge. Now these oppositely charged ions, they will attract each other. And the compound that gets formed is called an ionic compound.