What is the difference between a crystalline and amorphous structure?

Question

can relate to drugs or polymers

Answer 1

In crystalline matter everything is oriented in an identical repeating matter. For example, an auditorium where everyone is regularly spaced and all facing the same way can be thought of as a "2d crystal." In amorphous structure everything is irregularly oriented and does not have regular spacings. Crystalline materials have very well defined properties (melting points, optical properties, diffraction), and amorphous materials do not (no distinct melting points, more complicated optical properties, etc.).

With specific regards to durgs or polymers, most polymers form amorphous materials. Drugs, being smaller and well-defined molecules, can be crystallized much more easily, although they are not necessarily crstalline. However, crystals are useful for determining structures, and usually correlate very well with high purity, which is very desirable with medicines.