X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract in specific directions. By measuring the angles and intensities of the X-ray diffraction, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal and the positions of the atoms, as well as their chemical bonds, crystallographic disorder, and other information.
A powder X-ray diffractometer in motion
Drawing of square (A) and hexagonal (B) packing from Kepler's work, Strena seu de Nive Sexangula.
One of the copper sulfate X-ray interference patterns published in Von Laue's 1912 paper.
Although diamonds (top left) and graphite (top right) are identical in chemical composition—being both pure carbon—X-ray crystallography revealed the arrangement of their atoms (bottom). In diamond, the carbon atoms are arranged tetrahedrally and held together by single covalent bonds. By contrast, graphite is composed of stacked sheets. Within the sheet, the bonding is covalent and has hexagonal symmetry, but there are no covalent bonds between the sheets.
X-rays are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it X-radiation to signify an unknown type of radiation.
Natural color X-ray photogram of a wine scene. Note the edges of hollow cylinders as compared to the solid candle.
Example of a Crookes tube, a type of discharge tube that emitted X-rays
Wilhelm Röntgen
Taking an X-ray image with early Crookes tube apparatus, late 1800s. The Crookes tube is visible in center. The standing man is viewing his hand with a fluoroscope screen. The seated man is taking a radiograph of his hand by placing it on a photographic plate. No precautions against radiation exposure are taken; its hazards were not known at the time.