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We're going to pick up where we left off on Monday. And where we left off was we were dissolving stuff. We talked about how things dissolve. Why does something dissolve maybe in this solvent versus that? And how does it dissolve? And what makes them-- and then we say, well, what if we had something and we wanted it to dissolve all the way until it couldn't dissolve anymore? Well, that's called saturation, right? And we talked about that. We talked about how if you had a general reaction, maybe we had something like this, aA plus bB goes to and comes back from cC plus dD, then this reaction can happen in both ways, right? And so the general concept that we called a reaction quotient, reaction Q, is equal to-- remember, it's equal to the concentrations raised to those stoichiometric coefficients. And it's the products over the reactants. OK, so that's what we-- now then, we say, well OK, that's a thing that has to do with maybe-- where's that...

But I want to pick up where we left off on Monday. We were talking about the three Bravais lattices. There a couple more things that I want to say about them. What we captured, the key essence, apart from they're being these cubic crystals and the different elements that form them, is this idea that you can go from the unit cell, once you know the unit cell, you can get the atomic radius. So that's kind of cool. Because you know information about things like, for example, packing. So then we had the packing fraction, the atomic packing fraction. Calculated that. The maximum, the max packing fraction. Packing fraction. We calculated things like the closed pack direction. Well, you can also go to things like the density. Once you know how to go back and forth. And so for example, if I want the density of a material, that's grams per centimeter cubed, right? That's the density. But you could write the density in terms of the things we talked about on Monday. ...