Crystallography is the study of the formation and structure of crystalline substances. It includes the study of crystal formation, chemical bonding in crystals, and the physical properties of solids. In particular, crystallography is concerned with the internal structure of crystals including substances that were not previously thought capable of forming crystals, such as DNA.
X-ray crystallography is the study of crystal structure by means of X-ray
diffraction. Each substance has a different crystalline structure. The atoms, molecules, or ions
in a far too small to affect a beam of light. X-rays, however, have a shorter wavelength than visible light and diffracted by the lattice.
X-ray crystallography allows the details of the structure to be recording by bombarding a crystal sample (1) with a beams of X-rays (2). The X-rays are created by bombarding a tungsten anode (3) with electrons in a vacuum (4). A slit (5) focusses the X-rays on the crystal. The distance between the atomic planes in the crystal either reinforces (6) or cancels out (7) the X-rays. When the ray is reinforced the emerging X-ray (8) creates a spot (9) on photographic film. The pattern of the spots can be used to deduce the exact structure of molecules.