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It's our last Friday. Did I hear an, "Oh?" Thank you for that one "oh." It's OK. I'll take what I can get. It's our last Friday, and so next week is our last week. We have class on Monday, and Wednesday will be the last class. And we've got one more smallish topic to cover after this, which is diffusion, and we'll wrap up on Wednesday. But today, I want to keep talking about polymers. So this is our polymer week. And I want to go back to the properties I've put here, the properties we've talked about. Right? So on Monday, we focused on what a polymer is, and we focused on the ways you make it. All right? The radical initiation, chain, addition, and the condensation polymers that you know, the condensation where you have two different mers. And then on Wednesday, we talked about things that matter, kind of like engineering polymers. Like what are the properties of the polymers that you can change, that we can change? All ...

Happy Friday. How is everyone? Woo! Woo! Woo! Cool. Cool. I am excited. We're going to keep talking about XRD today. We're going to pick up where we left off. So I filled in some numbers. And then, we're going to fill out this chart and really get to a deep understanding of XRD. I'll also talk about Moseley's law and a little bit about another type of XRD that is done. Now, where were we? Oh, OK. We were here. So on Wednesday-- and before we fill this chart out, I want to go back and make sure we, kind of, get this. Right? We talked about the Bragg condition. And we talked about how the unique thing about x-rays is that their wavelengths are right in that, sort of, precious distance regime of the spacing of atoms in a crystal. And so if I shine them on the crystal, then they can diffract. And they can have constructive and destructive interference, but only if they line up. And that's what the Bragg diffraction tells us. It tells us the the Bragg c...