 Okay, at this point we are going to start talking about atoms in a tremendous amount of detail, and we are going to talk about what atoms are made of. Before we get to that, I want to talk about a dead guy, he is very dead, named John Dalton. I think he lived a couple of hundred years ago. I think he's given credit for being the first person to come up with a description of what materials are made of that uses the idea of atoms and is pretty close to the modern understanding of what materials are made of. So this is what John Dalton said, let's see, he said all material objects are made up of tiny particles called atoms. So to you and me, that's not so surprising. Back when he said it, it was probably reasonably surprising. So there were probably disagreements over what material objects were made of. Second thing he said is that there are different elements and all elements that belong to the same group, all elements that are the same, all atoms that are the same element are similar to each other and they are different from atoms of other elements. In other words he said, hey, there is a copper atom and I am going to abbreviate it CU. If I have another copper atom over here, these two guys are similar to each other and they are different from, let's say, an oxygen atom which I am abbreviating with the letter O because that is the simple for oxygen. So again, probably not surprising information to you, but he is sort of the first person to state that clearly. Let's see. So this, at least for the time being, is going to be my cartoon drawing of a bunch of atoms and because they are all more or less the same size, more or less the same color, I am going to consider them to be identical atoms. They are the same type of atom, let's say. John Dalton said some more stuff. He said that he is the person who came up with the definition of a compound. He said two or more types of elements, two or more types of elements or atoms combined, in other words, they stick together to make something called a compound. He also said that a specific compound is always made of the same types of atoms arranged in the same ways. So what this is basically saying is, if I have a water molecule in my toilet and I have a water molecule on the French Riviera, they are made of the same types of atoms arranged in the same ways. Again, this probably isn't surprising to you, but my suspicion is that there were disagreements about whether the same types of materials were made of the same types of atoms and molecules or not a couple of hundred years ago. But he is the person who said, look, this is probably the way it is. Chemical reaction, Dalton has given credit for coming up with a reasonable definition of what a chemical reaction is, and he said that it involves rearrangement, separation, or combination of atoms. And I showed you that in a previous lecture. I showed you. These are a couple of molecules. There's always two red ones attached to a blue one. There's always two red ones attached to a blue one. And a chemical reaction might involve basically ripping the atoms off of each other and free attaching them in different ways. So I ripped the blue ones off of the red ones and I attached the blue ones to each other. I ripped the red ones off of the blue ones and I attached the red ones to each other. This is, according to John Dalton and us, a chemical reaction. So he's sort of given credit for being the first person to come up with that description. One of the other things that he said, and this is where we're going to stop as far as John Dalton is concerned, is he said the atom is the smallest piece of an element that still behaves like that element. So if that doesn't make sense to you, let me try and explain that here. So this is supposed to be copper penny. And if you could zoom in and look, you might be able to see the atoms. And because this penny is made exclusively of copper atoms, you would think that, well, the atoms would look more or less alike. So I've drawn a whole bunch of atoms that more or less look identical to each other. They're kind of round and gray, same size. So what he's saying is, look, if I have this atom over here that I just circled and I compare it to another copper atom that I just circled, they're going to behave more or less similarly. They're going to behave just like each other. And they're going to behave differently than other types of atoms, like an oxygen atom or a carbon atom or something like that. But then what he's saying is, you can't go any further than this. You can't get any smaller than this copper atom. If you try to break this into smaller and smaller pieces, maybe you can break it. But those pieces are not going to behave like copper atoms anymore. They're going to behave like something weird that he didn't really understand because people didn't know what pieces atoms were made of yet. To give you a slightly more realistic explanation, these are a bunch of cars that I will never be able to own. They cost a tremendous amount of money. And there's a bunch of them there. They're more or less identical to each other. They both go very fast. They all go very fast. And they all cost a lot of money. But you can imagine a situation where I removed all of the cars except the one in the front. It's still a car. Just like this atom over here is still an atom. Even if I remove all of the others from the area, this guy is still a copper atom, and this is still a car. But then I can break this car into smaller and smaller pieces. I can break it into a wheel. I can break it into the doors, things like that. But the wheel, all by itself, is not a car. And the doors, all by themselves, are not a car. They're pieces of a car. So eventually, you can break things into smaller and smaller pieces, where they stop being a certain type of unit. So you can remove all of the atoms, except for one, in this penny. So imagine you cut away all pieces of this penny, except for one tiny little atom. There's my copper atom. And what I'm telling you, and what John Dalton is telling you, is that that atom was just like all of the others that we cut away. But then what he's saying is, you can smash that little copper atom into smaller pieces. But once you do that, it stops behaving like a copper atom. And those pieces, he didn't understand what they were. But we're going to talk about them on the next video.