The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Bibliographic Entry||Result |
|Brown, LeMay & Bursten. Chemistry The Central Science. Upper Saddle River, NJ: Simon & Schuster, 1997: 227, 412-413.||"Atomic radii allow us to estimate the bond lengths between different elements in molecules. For example, the C-C bond length in elemental carbon (diamond) is 1.54 Å, implying a radius of 0.77 Å."||0.142 nm |
|"In graphite the carbon atoms are arranged in layers of interconnected hexagonal rings as shown in Figure 11.42(b). Each carbon atom is bonded to three others in the layer. The distance between adjacent carbon atoms in the plane, 1.42 Å, is very close to the C-C distance in benzene …."||0.341 nm |
|"The layers, which are separated by 3.41 Å, are held together by weak dispersion forces."||0.154 nm |
|Burdett, Jeremy K. Chemical Bonding in Solids. New York: Oxford University Press, 1995: 152.|| |
|Harrison, Walter A. Electronic Structure and the Properties of Solids: the Physics of the Chemical Bond. San Francisco: Freeman, 1980: 90.||"Graphite is a simple planar structure in which the carbon atoms are arranged as in Fig. 3-10. The nearest neighbors are separated by 1.42 Å (in diamond they are separated by 1.54 Å), but the distance between successive planes is much larger (3.4 Å) …."||0.142 nm |
|Desch, Cecil A. The Chemistry Of Solids. Ithaca, NY: Cornell University Press, 1934: 180.||"The simplest example of a layered lattice is that of graphite. The structure is shown in Figure 55. The atoms of carbon are very closely packed in the basal planes, the distance between their centers being only 1.42 Å, which is even closer than in diamond, 1.53 Å. On the other hand, the successive sheets of atoms are very widely separated, the distance being no less than 3.41 Å."||0.142 nm |
|Saada, David. Diamond and Graphite Properties. 22 June 2000.|| |
|0.1421 nm |
Carbon is an interesting element. This is largely due to the fact that it has four electrons in its valence shell. This shell can hold a maximum of eight electrons. This allows carbon to bond with up to four other atoms at a time. Because of this, carbon forms an enormous number of compounds of varying size and shape. For instance, carbon atoms form the substances diamond and graphite. Graphite is soft and slippery, while diamond is the hardest substance known to man. How is it possible for one element to form substances with such different properties?
Carbon atoms are unique in that they are able to form many different kinds of bonds with other carbon atoms. Graphite is layered. Within each layer, carbon atoms form strong covalent bonds in a hexagonal pattern (planar). A covalent bond is one in which one or more pairs of bonding electrons (valence) are shared. Carbon forms a double covalent bond, which means that two pairs of bonding electrons are shared. This type of bond is very strong. The bond length is 0.142 nm. The bonds between atoms of carbon in the layers of graphite may be strong, but the bonds that are formed by carbon atoms between layers are quite weak. These atoms are held together by Van Der Waal's forces. This kind of attraction is caused by shifts in the cloud of electrons surrounding carbon nuclei. When the electron cloud shifts in a certain way, the carbon atom may become slightly negatively charged on one side and slightly positively charged on the other. The carbon atom becomes a dipole and induces other carbon atoms to become dipoles, as well. Since the layers are only weakly attracted to each other, they can easily slide past one another. This is why graphite is used in pencil lead. The distance between layers is 0.335 nm.
Carbon atoms in diamond are covalently bonded and are arranged in a three-dimensional tetrahedral structure. All bonds are of the same length, 0.154 nm. In this rigid network, none of the carbon atoms can move. This accounts for the fact that diamonds are so hard and have such a high melting point.
Graphite is a good electrical conductor. Diamond is a good insulator. Diamond is an excellent abrasive. Graphite makes a good lubricant. Graphite is opaque. Diamond is transparent. It is because of their respective structures that two substances composed solely of carbon atoms can have such different properties.
Alice Warren-Gregory -- 2001
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