Diamond molecular structure

Crystals of high purity metals are very soft, while high purity diamond crystals are very hard. Why are they different What features of the atomic (molecular) structures of materials determine how hard any particular crystal, or aggregate of crystals, is Not only are crystals of the chemical elements to be considered, but also compounds and alloys. Glasses can also be quite hard. Is it for similar reasons What about polymeric materials ... 

Giant atomic (or giant molecular) structures, diamond... 

There are four allotropic forms of manganese, which means each of its allotropes has a different crystal form and molecular structure. Therefore, each allotrope exhibits different chemical and physical properties (see the forms of carbon—diamond, carbon black, and graphite). The alpha (a) allotrope is stable at room temperature whereas the gamma (y) form is soft, bendable, and easy to cut. The delta A allotrope exists only at temperatures above 1,100°C. As a pure metal, it cannot be worked into different shapes because it is too brittle. Manganese is responsible for the color in amethyst crystals and is used to make amethyst-colored glass. 

At pressures of 13 GPa many carbonaceous materials decompose when heated and the carbon eventually turns into diamond. The molecular structure of the starting material strongly affects this process. Thus condensed aromatic molecules, such as naphthalene or anthracene, first form graphite even though diamond is the stable form. On the other hand, aliphatic substances such as camphor, paraffin wax, or polyethylene lose hydrogen and condense to diamond via soft, white, solid intermediates with a rudimentary diamond structure (29). 

The two most common elemental forms of carbon are diamond and graphite. Diamond, one of the hardest substances known, is used for industrial cutting tools, whereas graphite, a slippery black substance, is used as a lubricant. Their physical characteristics are so different because their molecular structures are very different. 

FIG. 3(a) Model of C70 molecular structure illustrating one ensemble of four fused hexagonal rings as a possible diamond nucleation site, (b) Model of (111) diamond nucleation on C70 derivative. The darker and larger atoms represent C, and the lighter and smaller atoms represent H,... 

Several cluster models have been tested to account for patterns of small clusters (p = 1 or 2 bar in Fig. 18). First, clathrate models have been examined. The most popular of these consists of a regular dodedecahedron with one H2O molecule at each of the 20 vertices and possibly one additional molecule at the center. In this model, HjO molecules form regular pentagons with a molecular angle HOH of 108°, which is intermediate between 104.5°, the value for the free molecule, and 109.5°, that for tetrahedral bonding in the diamond cubic structure. Such a clathrate model, stabilized by an additional proton, accounts well for mass spectrometry results, but is found to be far too symmetrical to account for the structure of neutral clusters. An amorphous model,derived from Polk s random dense packing, has been tested. This... 

In Group IV there is a change from the essentially covalent 4-coordinated structure of diamond. Si, Ge, and grey Sn(iv) through white Sn(ii) to Pb, with a c.p. structure characteristic of many metals. Group V begins with the normal molecular structure of N2 and white P (P4), but phosphorus also has the deeply... 

The difference between the forms involves either (1) crystalline structure (2) the number of atoms in the molecule of a gas or (3) the molecular structure of a liquid. Carbon is a common example of (1), occurring in several crystal forms (diamond, carbon black, graphite) as well as several amorphous forms. Diatomic oxygen and diatomic ozone are instances of (2) and liquid sulfur and helium of (3). Uranium has three crystalline forms, manganese four, and plutonium no less than six. A number of other metals also have several allotropic forms which are often designated by Greek letters, e.g., a-, y-, and A-iron. 

Diamond, R., On the multiple simultaneous superposition of molecular structures by rigid body transformations. Protein Sci, 1992. 1(10) p. 1279-87. 

The characteristic properties of the covalent bond discussed above impose severe restrictions on the possible types of crystal structure in which such bonds may occur. Since the number of neighbours to which a given atom may be bound by covalent bonds is limited to the covalency of that atom, and since this covalency is usually small, the vast majority of structures containing the covalent bond are molecular structures in which covalent forces occur within discrete molecules but in which the molecules are bound to one another by forces of a different kind. There are, however, a number of structures in which the binding throughout is due to covalent forces, and of these the simplest is that of carbon in the form of diamond. 

Olszyna A, Konwerska-Hrabowska J, Lisicki M (1997) Molecular structure of E-BN. Diamond Relat Mater 6 617-620... 

The continuous reduction in size of a solid finally leads to a situation where the original solid state properties can be only partially observed or may be even completely lost, as these properties are exclusively the result of the cooperation between an infinite number of building blocks. Further reduction of size finally leads to typical molecular behavior. On the other hand, even here are structural relations to the bulk occasionally detectable. For instance, the arrangements of the sp hybridized carbon atoms in cyclohexane or in adamantane can easily be traced back to the diamond lattice, whereas benzene or phenanthrene represent derivatives of the graphite lattice. However, neither cyclohexane, benzene, nor phenanthrene have chemical properties which are comparable with those of the carbon modifications they originate from. The existence of the above mentioned Q, C]o or Ci4 units is otUy made possible by the saturation of the free valencies by hydrogen atoms. Comparable well known examples for other elements are numerous, for instance the elements boron, silicon, and phosphorous. Figure 1-1 illustrates some of the relations between elementary and molecular structures. 

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