After spending some time looking at redox reactions, I want to go back and look at double replacement reactions. In particular, I want to look at this example that we've already seen. Remember the double replacement reactions with the two sets of dance partners that swapped. The example we had seen previously was sodium chloride and silver nitrate. When they swap partners, you get sodium nitrate and silver chloride. I highlighted in this reaction that this is a precipitation reaction. We define precipitation as having two aqueous solutions forming a solid. The aqueous sodium chloride and the aqueous silver nitrate are forming a solid silver chloride. That is a precipitation reaction. I want to talk about what it means to be aqueous. What does it mean to be soluble? In the first trimester, we talked about a property of ionic compounds. We said that many are soluble in water, many of them dissolve in water. When they do, they are electrolytic. Why is it that ionic compounds conduct electricity when they are dissolved in water? We saw that covalent compounds were not electrolytic. Why are ionic compounds? When you look at the dissociation process, when you look at an ionic compound breaking apart and dissolving in water, we see that it is the individual ions that separate. When sodium chloride dissolves in water or when sodium chloride is aqueous, you no longer actually have sodium chloride bonded together. You have free-floating chloride ions and free-floating sodium ions just drifting around in the water. That's what it means when you have an aqueous ionic compound. The ions are no longer bonded to each other. They are dissociated. But we said that some ionic compounds, dissociate or dissolve in water, some ionic compounds are soluble. However, some ionic compounds are not soluble. They are insoluble. When you put them in water, they don't dissolve. Fortunately, there is a table in the book. This is table 8.1 that has rules for figuring out which ionic compounds dissolve in water and which don't, which ionic compounds are soluble and which are not. We're going to be relying on these solubility rules in the following videos to help us predict the outcomes of these chemical reactions. The solubility rules are also found on the back of your periodic table. They're a good thing to refer to. What we're going to do for these precipitation reactions is we're going to write three types of equations. We're going to start out with the most familiar, a molecular equation. This is what we've been doing all along. These molecular equations show all the compounds bonded together and then in a double replacement reaction, they would show the dance partner switching. So this is nothing new. I want to take some time, however, to look at some complete ionic equations. These complete ionic equations show the dissociation of the ions in solution. It shows that the aqueous solutions are in fact broken apart into their individual ions. I also want to write some net ionic equations. These net ionic equations don't show all the ions. They just show those that are changing in the reaction. Net ionic equations exclude something called spectator ions. I'll show you what that means when we get into the examples.