 In order for us to fully discuss electronics, we're going to do a quick review of the atom and we're just going to discuss some parts that pertain to us as electricians. So let's talk about the three main parts here. First and foremost here, and not foremost, but first we've got this middle guy here. This fellow right there, and we're going to give him a name. We're going to call him the nucleus. So let's get that. Nucleus. So that's the nucleus. It's comprised of protons and neutrons. It's got a net positive charge because your protons have a positive charge. Your neutrons have a neutral charge or no charge. Next up, we have these guys that are orbiting around these. We've got these three guys here. These are called our shells. Now our one closest to the nucleus will have two. The one next to it will have eight, and it goes on and on and on outwards. What we are mainly concerned about with is the third part, and we're going to call this guy right here, our valence. So let's talk about that, our valence. Now our valence is important to us because it is the electrons that are on the valence. These guys right here that are important to us because those are the ones that can break free and certain moving. And that's what current flow is. Current flow is just electrons that move. And so if we can break these guys free and get the moving, we are going to get electron flow. Now looking at this guy here, the one atom I've got drawn, I've got an aluminum atom. You can tell that by the AL, which is aluminum in the periodic table. The aluminum atom will have three valence electrons. That makes it a good conductor. So let's just discuss a little bit about the conductors. Now before we get too far into conductors, you'll notice here on this drawing I've got, I've only got one shell. That's because like I said in the previous slide there, we don't concern ourselves with these inner shells. We are concerned mostly with this outer shell, the valence shell. Now in this one here I've got one valence electron. This guy here, he is easy to break free because he has no friends holding his hands. It's like a gamer red rover when we're talking about the valence shells. If a force is pushed on this guy, if you give him a little bump, he will easily break free and flow. Which is what current flow is as I discussed before. So when we look at these guys, and this one here is a copper atom. It has one valence electron, which means it can break free. Aluminum will have three. Which means that if we have any atoms that have between one and three valence electrons, they are good conductors. So it's just good to note that one is copper. Let's just get that written in here. Copper and three is aluminum. And those are good conductors. Between one and three makes a good conductor. Now if we have got a good conductor, what's the opposite of a conductor is going to be an insulator. So let's take a look at that. Now if one to three valence electrons were a good conductor, then we're looking at this guy here. If you notice, if you count up his electrons, and I'll count them up for you, one, two, three, four, five. He's got five electrons. Like I said before, like a game of red rover, these guys are all locked together by some nuclear force. It is harder to get them to break free. They kind of hold each other there. It is possible if you exert enough force on it, it can break them free. But for the most part, they're going to hold. Now with that force, it's going to kind of stretch the atom out and it'll turn into more of an elliptical type shape. We'll talk about that when we talk about capacitors. Now right now, we've got this guy here, which is out of five. Now if we look at these ones anywhere between five and eight. So anywhere between five and eight valence electrons makes a good insulator. So one to three is a good conductor and five to eight is a good insulator. If we've got one to three and five to eight, we're missing a number there. It's four. So let's take a look at a semiconductor. So a semiconductor is going to have four valence electrons. We've got the one, the two, the three and the four there. It's not a good conductor. It's not a good insulator. Basically on its own, it's almost useless. But what we're going to see in the next video is if we get a bunch of these guys together, these semiconductor atoms, they're going to form what's called a crystal. And then depending on what we do to that crystal, it can actually either act like a good conductor or a good insulator. It becomes almost an electrical valve. I don't want to get too far ahead of myself. So this is your semiconductor. Now, semiconductors are made of these two common types. There's the silicon and the germanium. The most common type is the silicon though, which the reason why we like silicon so much is it can resist heat a lot better than germanium can. And we're going to talk about negative temperature co-efficiency in another video. But as this guy heats up, it ends up having its resistance go down, which is kind of the opposite of every other kind of substance out there. And when that happens, the current goes up, it heats up, its resistance goes down. You start to see what I'm saying, it starts getting out of control, then cascades out of control. Silicon's better with standing heat than germanium. Also, silicon forms 27.7% of the earth's crust. Only oxygen is more common. So you can find it everywhere. So we can take this stuff and we can turn it into a crystal. And as we'll see in the next one, if we dope it, we can put it into a diode. So that's what the next video is going to go into. We'll see you in the next one.