 Hello everybody. We're back here on this glorious day to begin our study of chemistry in our biology course. Perhaps you will be happy to know that there are only two lectures that we're going to devote to our study of chemistry. I say you may be happy. That might also make you sad. You might feel like, oh my god dude, we need like 10 lectures to understand this chemistry stuff that you are presenting to us today, Riggs. And I would agree with that. Chemistry is a very, very complex and mathematical and conceptual science and it's a whole class. Many of you will follow up this biology course with a course in chemistry before you take something like human physiology or microbiology. The chemistry is fundamental and because I am a physiology teacher, I know the chemistry that counts. I know the stuff that is going to be most worth your time and energy to understand the things moving forward. If you've looked at any of the stuff I've done in the past, I effectively doubled the amount of chemistry that we're going to talk about in this class for this redo of the video lectures and I did that on purpose. I feel like chemistry is so fundamental and these concepts that we're going to talk about today are pretty, they're foundational and you will see them again and again and again. So if any of it is unfamiliar to you, know that it's worth your time to commit it to memory and it will help you understand the stuff that's coming up for us. So today, just like in the last lecture, I'm going to start us off with a few definitions. Unlike the last lecture, I'm going to start us off with some definitions that hopefully are not at all controversial, although they are kind of weird. They kind of all they're, they rely on each other to define each other. You'll see what I mean in just a second. The first definition that I want to have in our brains, very clear before we get moving any further is matter. What is matter? And again, it's just helpful to have a good clean definition. Matter is anything with mass that takes up space. So anything with mass and volume, volume is a measure of how much space something takes up. So matter has to have mass, it has to weigh something and it has to take up some space. It has to have volume. Well, the good news is the thing we're going to spend the most time talking about is the atom. And the atom is, it's a, I'm going to get kind of weird here. It's the smallest particle of an element. But it is the fundamental unit of matter and the fundamental unit of matter. So all matter is made of atoms and atoms are the smallest particles of elements, which guess what our next definition is. An element is a type of atom. I am sorry, but I think of things in flavors. And I think of elements as different flavors of atoms. When we look at the structure of an atom, we will see that all atoms share certain characteristics. They're built from the same subatomic particles. But depending on how we mix and match the subatomic particles, we get different elements. The elements show up. I'm just going to come back and show you this again. The elements show up in and are organized in the periodic table of elements. And we will look at that in more detail as we as we move along. Wait a minute. Now I got to make that, make that go away so we can get back to our definitions because we have one more definition that I just wanted to find right off the top. Molecule. Oh, good gracious. You can read that. Can't you? Molecule. A molecule is two or more connected atoms. Now, if you have taken chemistry or taught chemistry, you might have something to say about my definition of a molecule. I am, for our purposes in this class, I'm not going to mince molecule versus compound versus ionic. If it's more than one atom connected together, we're going to talk about how they get connected. I like connections. If it's more than one atom connected to each other than that, we're going to call that a molecule. All right, that's it. Those are our definitions. Now let's look at the atom itself.