 There are three types of solids. We're going to look at an ionic compound, a metallic compound, and a covalent compound. Ionic compounds are held together by electrostatic forces. We're going to look at the characteristics of some of those. First, let's look at the electrical conductivity of the solid. I have a conductivity device, and this is just a battery connected to LEDs, and if the leads are crossed with a conductive material, then the lights will come on. So if we put our conductivity probe on this solid piece of sodium chloride, no lights come on. If we put them on this piece of tin, the lights come on. So tin is a conductor. This is naphthalene. We have a solid piece of naphthalene. It's not a conductor. Let's see if these are soluble. If we add a little bit of water, our substances, let's see if they dissolve. And if they dissolve, do they conduct electricity? So we're going to put our conductivity probe back into the solutions. Now notice what happened with our sodium chloride. It didn't conduct as a solid, but it does conduct in solution, and it's dissolving. You can see that there's still some there, but there's not as much as there was before as a solid. Well, it doesn't look like the tin is dissolving in water. We still have a nice large chunk of metal. And since it's not going in solution, there's really nothing to test. In our naphthalene, it looks like the same things happened. None of it seems to have dissolved. We'll test to make sure, but there's nothing in solution. We know there are some covalent compounds that are water soluble, like sugar, because you put sugar in your tea or in your Kool-Aid. So let's try sugar and see what it does if we dissolve it in water. So our sugar is dissolved in water. And let's check and see if it's conducting. And it's not. So we have a solution that is covalent and dissolves in water does not conduct electricity. Ionic compound like our sodium chloride does conduct electricity.