 Okay, everybody, Dr. O here. Protons and neutrons are critically important, but if we really want to understand the behavior of atoms and how they react, we have to understand electrons, so it's like a deeper dive in looking at electrons. So we're going to look at what are called electron shells. We've already talked about the fact that electrons are actually in clouds. We can really only predict their speed or the general location where they are, but these ring structures, they're going to be the most important as far as basic understanding here. So an electron shell is going to be all the electrons that stay in a certain energy level. And as you can see here, hydrogen and helium are the only two elements that only need one shell. And the first electron shell can only hold two electrons. After that, all the remaining shells we care about can hold eight, because we only really care about the first 20 elements on the periodic table. In human anatomy and physiology, there are certainly some exceptions, but so if you understand that the first shell can hold two electrons and all the other shells that we're going to talk about can hold eight, you're going to be perfectly fine. So hydrogen only has the one electron, so its outer shell is not full. So we'll talk about why that makes hydrogen so reactive. Hydrogen really wants to fill its outer shell. Helium's outer shell is full, and that's why helium is a stable inert gas because its electron outer shell is already full. It doesn't want to give up or take or share anything. It just wants to be left alone. It's already happy. But after that first electron shell that only holds two, the second shell and all the shells we care about after that are going to hold eight electrons. So here we see carbon. Its first electron shell is full with the two electrons. Its second shell is only half full. So it has four electrons in its outer shell and it wants eight. So it wants to be like neon sitting next to it. Neon, its first shell is full, and its second shell has all eight electrons full. That's why neon, just like helium, is going to be one of our noble gases. It is stable. It is inert. It does not want to react. Nitrogen really, really wants to add, remove, or share four electrons in order to be happy. And we'll talk about what makes carbon unique in a separate video. Carbon loves to bond with itself and loves to bond with hydrogen because it's trying to make itself happy. We'll use the carbon. We'll save the carbon example for later. All right. So here we see an example of how these different atoms are going to either gain, remove, or share electrons to become happy. Well, another term here is we talked about why electrons are important. The most important electrons are what are called the valent shell electrons. The electrons in the outermost shell, because those are the ones that actually are interacting with the world around them, they're the ones that are going to be reacting. You see here, you see oxygen. Those two electrons in its inner shell, they're not reacting. They're already happy because their shell is full. We only care about the six electrons that are going to be outside of oxygen. So another important term to note is the octet rule because any atom is going to gain, lose, or share electrons to make its outer shell full. And every outer shell, except for that first one there, wants eight electrons, which is why it's called the octet rule. Let's see how this matters in the real world. Oxygen has six electrons and it wants eight. Hydrogen has one electron and it wants two. So in one way, and these are going to be covalent bonds, we'll cover the bond types in just a moment. But one way that oxygen can be happy and two hydrogens can be happy is if they share electrons. So now you see that oxygen has all eight electrons it needs to satisfy the octet rule and be stable. But to do so, it had to share an electron with one hydrogen and share an electron with another hydrogen, which is why oxygen forms H2O. Two hydrogens are going to bond with one oxygen forming water. Now they're all happy. Hydrogen has the two electrons it needs, oxygen has the eight electrons it needs. So everybody's happy in this situation. This would be one way that this can occur. But everyone trying to be happy, every atom trying to fill its outer shell by either gaining, losing, or sharing electrons is going to lead to different bond types here. So the three basic types of bonds you're going to see are ionic bonds, covalent bonds, and hydrogen bonds. Now you'll see up on the top here two types of covalent bonds. I will cover them separately. But let's start with the ionic bonds in the bottom. The ionic bond is going to be anytime atoms gain or lose electrons to bond together to make sure they're happy. So you'll see here that sodium has that one electron in its outer shell. It once it gets rid of that extra electron, so now its outer shell is full. Chlorine really needs one electron, so it's going to take it. So now sodium has made itself happy by getting rid of the one extra electron. Chlorine has made itself happy by gaining an electron. That transfer of electrons has now made them a positive ion, sodium, also known as a cation, and made chlorine the negative chloride ion, also known as an anion. Now they have opposite charges and they're attracted to each other. So that's going to be ionic bonds, the transfer of electrons. Covalent bonds keyword is shared, just like I showed you with that molecule of water. When atoms share electrons to become happy, those are called covalent bonds. And then hydrogen bonds are going to be a special type of bond. We're going to talk about later a dipole-dipole interaction where you have hydrogen from one water molecule or anything really, the typical example we talk about is water. So one hydrogen is going to bond with a fluorine, oxygen, or nitrogen from another molecule. And those are going to form these special hydrogen bonds, and the reason they're so important, I mean they do lots of things. They play a role in the structure of DNA, the structure of proteins, but hydrogen bonds are what make water so special. Without water we cannot have life, but water wouldn't be anything special if it weren't for hydrogen bonds. We'll cover that later as well. All right, so that's the electrons, the valence electrons, why they're so important, and the types of bonds that end up being created, because all these atoms want to be as happy. And they either make themselves happy by giving things up, getting things, or sharing things. Okay? And by things, I mean electrons. All right, I hope this helps. Have a wonderful day. Be blessed.