Molecules are arranged in specific patterns in all materials. This is the basic theory of matter. These atoms are arranged in the specific manner because of the interconnecting bonds between the atoms. The stronger the bonds, the more tightly the atoms and molecules are held together.
This causes different states of matter. For instance, in solids, the molecules have tight chemical bonds between them. This causes the molecules to be tightly packed together and vibrating about their positions. In liquids, the bonds are weaker so the molecules are relatively free to glide about but are still close together. In gases, they are far apart.