![]() ![]() In addition, these planar arrays are held together by weaker forces known as stacking interactions. These planar arrangements extend in two dimensions to form a horizontal, hexagonal "chicken-wire" array. In the first, each carbon atom is bonded to three other carbon atoms and arranged at the corners of a network of regular hexagons with a 120-degree C-C-C bond angle. These atoms have two types of interactions with one another. The carbon atoms in graphite are also arranged in an infinite array, but they are layered. This means that when yellow light passes into a diamond and hits a second face internally at an angle greater than 24.5 degrees, it cannot pass from the crystal into the outside air but instead gets reflected back to the inside of the gemstone. For yellow light, for example, diamond has a high refractive index, 2.4, and a low critical angle of 24.5 degrees. The "brilliance" of diamonds stems from a combination of refraction, internal reflection and dispersion of light. This property gives rise to the "fire" of diamonds. The greater the dispersion, the better the spectrum of colors that is obtained. As a result, the gemstone acts like a prism to separate white light into rainbow colors, and its dispersion is 0.056 (the difference). This means that the refractive indices for red and violet light are different (2.409 and 2.465, respectively). ![]() Diamond also conducts sound, but not electricity it is an insulator, and its electrical resistance, optical transmissivity and chemical inertness are correspondingly remarkable. ![]() It is the best conductor of heat that we know, conducting up to five times the amount that copper does. Diamond will scratch all other materials and is the hardest material known (designated as 10 on the Mohs scale). The hardness of a crystal is measured on a scale, devised by Friederich Mohs, which ranks compounds according to their ability to scratch one another. Because of its tetrahedral structure, diamond also shows a great resistance to compression. This accounts for diamond's hardness, extraordinary strength and durability and gives diamond a higher density than graphite (3.514 grams per cubic centimeter). It is a strong, rigid three-dimensional structure that results in an infinite network of atoms. Each carbon atom is attached to four other carbon atoms 1.544 x 10 -10 meter away with a C-C-C bond angle of 109.5 degrees. In a diamond, the carbon atoms are arranged tetrahedrally. The differing properties of carbon and diamond arise from their distinct crystal structures. The way the carbon atoms are arranged in space, however, is different for the three materials, making them allotropes of carbon. Miriam Rossi, a professor of chemistry at Vassar College, provides the following explanation:īoth diamond and graphite are made entirely out of carbon, as is the more recently discovered buckminsterfullerene (a discrete soccer-ball-shaped molecule containing carbon 60 atoms). ![]()
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