 Okay, as you remember from the previous video, atoms are made of three different particles or three different parts which I'm circling here. This video is going to be devoted exclusively to talking about protons. So we're going to ignore neutrons and electrons for the moment. So I want to talk about something called atomic number, which is related to protons. Every element, and if you remember from an earlier video, I said there's about 118 different elements, 118 different elements or different types of atoms. Every element has a different atomic number. The atomic number is the number of protons in an individual atom. So for example, hydrogen has an atomic number of one. That means H atoms, H is the abbreviation for hydrogen, H atoms all have one proton. They don't have two, they don't have zero, they all have one. If they had some other number other than one, they would be a different type of atom. Helium has an atomic number of two. Hopefully it's obvious to you, this is the abbreviation for helium. It's obvious to you that all helium atoms have two protons in them, and if they didn't have two protons, they would not be helium. And you can keep going on and on. Lithium has an atomic number of three. This is the abbreviation for lithium or the symbol for lithium, and all lithium atoms have three protons. So punchline here is that atoms of the same element always have the same atomic number, and which means they always have the same number of protons. On this slide, I am going to talk about or maybe reveal to you a little bit of information about the periodic table. We talked about the periodic table before, and here's a very relatively simple version of the periodic table. Each box is supposed to give you information about one particular type of atom or one particular type of element. We can look at this particular box over here, and it has a capital letter h. That's the symbol for hydrogen, and you'll notice that there's a number here written above the h. That's the atomic number. That tells you that all hydrogens have one proton. And now you can see something about the periodic table. If you read it like you're reading a sheet of paper in English, you read each row, and the first element has an atomic number of one. The next element written in the periodic table has an atomic number of two. And then you start on the second row. Third element has an atomic number of three. The fourth box or the fourth element has a four, and on and on and on. The periodic table is arranged in order of the number of protons that each element has. Starting with the number one, so hydrogen has the smallest number of protons, then number two. And on and on and on. And if you read this row after row after row, the numbers all just go up by one. What that's telling you is that each box or each element basically has one more proton than the last one. Another way of saying that is that each box has one more higher atomic number than the previous box. That's an introduction to atomic number. So now we're going to zoom in on the periodic table, and just to show you in cartoon fashion, remember that red circles are supposed to be my cartoon version of a proton. So because this number one is written here, this is going to be a cartoon version of a hydrogen atom because it only has one red circle, which means one proton, so it's a hydrogen atom. If we have four red circles, then we look up in the periodic table, we find the box that has a four written here, and this has to be a beryllium atom. This is my cartoon version of a type of beryllium atom because it's got four red circles or four protons. Or another way of saying that is the atomic number is four. Now I want to point out something, even though I said this a few minutes ago. I have not said anything about the number of neutrons in the atoms or the number of electrons in the atoms yet. We will get to that on subsequent videos. So now I want you to sort of play along with this and pause the video every so often. Basically look at this and tell me, use the periodic table to tell me what type of atom I am showing you. So pause the video. If you unpause, let's count the number of protons. It has one, two, three, four, five, six. Six protons. Atomic number. Another way of saying that is atomic number equals six. We look up the box that has a six in it and this is a cartoon version of an element with a symbol C. You can look up in a more detailed periodic table, the symbol C stands for carbon. So this is my cartoon version of a carbon atom. Here's a different one. Again, you can pause the video and try to guess what type of atom this one is. So pause. And unpause. Let's count the protons. One, two, three, four, five, six, seven and an eighth one in the middle there. So this thing, whatever it is, has eight protons. Or we can say that the atomic number is eight. We have to find the box in the periodic table. It has an eight. And it's a box with a capital letter O. O is the symbol for oxygen. So again, that's just counting protons or figuring out the atomic number. That's just another way of saying counting protons and figuring out what type of atom we have. So here's a question kind of in reverse. Again, you can pause the video but try to answer this question. How many protons does helium have? Or does a helium atom have, is what I should say. Does a helium atom have? And pause or unpause. And we look up HE in the periodic table. It has a number two written there. So all helium atoms have to have two protons. And that's, again, just another way of saying all helium atoms have an atomic number of two. And that's about it for atomic number and protons. Again, this is going to show up, this idea of atomic number, a number of protons is going to show up throughout the course. But that's it for the introduction.