So, from experiencing the world around us, we know that solids come in many different forms, sizes and shapes. Now, in this lecture, we're going to look at exactly that. We're going to examine the different type of structures formed by solids. So two main types of structures exist, and we'll talk about Crystalline Solids or simply crystals and amorphous solids. So let's begin with the crystalline solids. So all Crystalline Solids or simply crystals have a very well ordered shape or structure.