And basically, whenever an alkaline metal or an alkaline earth metal reacts with a halogen, these guys will always produce, or will most of the time actually will always produce ionic crystals. Now let's look at metallic crystals. Now, these guys consist of single metal molecules that are held together by a sea of electrons. And examples include any type of alkali metal or alkaline earth metal. For example, a composite which actually isn't an alkaline or alkali metal, but is a transition metal, but still it's a metal that has a metallic solid structure. Other examples are sodium metal or potassium metal or leafy metal or calcium metal.