Sodium chloride is an ionic crystal. Lithium chloride is also an ionic crystal. Calcium chloride or calcium dichloride is also an ionic crystal. 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.