 Let's start the day off today talking about shorthand notation of describing a chemical change or chemical process occurring. So in this case this is the shorthand notation that we as chemists use, we call it a chemical equation. In this case we're showing a reaction as opposed to a physical change, so a chemical change. How do I know that? It's because I'm having one substance, mercury-2 oxide, go to a different substance, make a different substance, that's mercury and oxygen, okay? So there's some essential features to this that we'll get into in a second, but I want to step back and recall that in the various, or in the past couple of weeks that you've been taking this class, you've seen chemical processes happen in the lab, you've talked about them, things like that, but we've never actually written them in shorthand how we do in chemistry class, okay? So this is the shorthand version of it, and we're going to have these essential features that you have to understand about this shorthand way of writing it. Well anyways, the first essential feature that you need to know is this thing in the middle is called the reaction arrow. The reaction arrow just tells us that some change has happened, okay? Chemical or physical change. In this case, it's a chemical change. To the left of the reaction arrow, you've got one set of molecules or compounds, atoms, compounds, particles, okay? To the left of it, we've got what we call the reactants. These are what was present in the in the mixture before anything happened, present in your reaction vessel before anything happened. On the right of the reaction arrow, we've got the product. So in this case, we've got process. So if I put a bunch of, if I put mercury to oxide under a bunch of heat, right, it's going to decompose into mercury and oxide. That's what this is telling me. Also some other essential features, particles in the reaction equation. At least the couple of them. There are these numbers, and in fact, there's nothing in front of there. Numbers are called co- if it's one, you don't put anything in there. Mercury to oxide decompose to form, and one molecule of oxygen. Crypto-oxygen just means that there's two oxygen atoms bonded together, and you guys know that. I haven't gone over. Are these things, okay? So after each particle, parentheses with a letter inside of it, okay? And those letters are either going to be S, Sands for solid. When it decomposes, it forms mercury metal, which is a liquid that isn't shown in this equation. It's called aqueous. This is when you form a solution where water is the solvent. We'll talk more about that later. Okay, so these are the essential features of a chemical equation.