Explanation atomistic

The elucidation of the factors determining the relative stability of alternative crystalline structures of a substance would be of the greatest significance in the development of the theory of the solid state. Why, for example, do some of the alkali halides crystallize with the sodium chloride structure and some with the cesium chloride structure Why does titanium dioxide under different conditions assume the different structures of rutile, brookite and anatase Why does aluminum fluosilicate, AljSiCV F2, crystallize with the structure of topaz and not with some other structure These questions are answered formally by the statement that in each case the structure with the minimum free energy is stable. This answer, however, is not satisfying what is desired in our atomistic and quantum theoretical era is the explanation of this minimum free energy in terms of atoms or ions and their properties. 

In summary, for Leukipp and Demokrit, the empty space between the atoms was a key assumption in their model, because, if particles were closely packed, they could not move and substances could not be mixed. When asking students to philosophise about the nature of matter, we indeed find parallels to the ancient Greek thinking, both to the so-called atomists and to the continuous ideas of Aristotle and others. For example, Leukipp s and Demokrit s explanation for the specific weight of substances corresponds to one student conception younger students especially tend to explain differences in the specific weight (but also hardness of substances) with differences in the closeness of particles (Fig. 10.6). They seldom take into account that the particles could have a different weight themselves. 

A tolerance factor [9,10] can be used to determine the phase transition in AB03 perovskite oxides, as given by t — (rA + > o )/V2(J b + ro), where rA, rB, and rQ are the ionic radii [11] of the A, B, and O ions, respectively. This indicates that the spatial margin relates to the type of phase transition. However, the atomistic explanation has not been given for the factor in order to distinguish between ferroelectric and antiferrodistortive phase transitions in AB03 perovskite oxides. 

And, yet, the transcendental aspect of elements was not completely forgotten and continued to serve an explanatory function in nineteenth-century chemistry but not necessarily a microscopic explanation. A chemist could be skeptical of atomistic explanations, as many were in the nineteenth-century, and yet could readily accept a transcendental explanation, for example, for the persistence of the elements in their various compounds. As was alluded to earlier, one of the benefits of regarding the elements as having a transcendental existence is that it provides a way out of the apparent paradox concerning the nature of elements when combined in compounds. Suppose that sodium and chlorine are combined to form sodimn chloride (common salt). In what sense is the poisonous metal sodium present in a sample of white crystalline common salt Similarly, one may ask how it is that the element chlorine, a green and poisonous gas, continues to exist in common salt. Clearly, the elements themselves, in the modern sense of the word, do not appear to survive, or else they would be detectable and one would have a mixture of sodium and chlorine able to show the properties of both these elements. The response available from the nineteenth-century element scheme is that simple substances do not survive in the compound but abstract elements do. ... 

Whereas others fail to give any account of combination... offering no explanation, e g., of action and passion—how in natural actions one thing acts and the other undergoes action, Aristotle recognized that the atomists had a clear idea of how to deal with these issues ... 

The two standard approaches in any treatment of kinetics [28] are to explain the system in terms of me thermodynamic driving forces (namely, VjJ.) or in terms of the fnndamental rate eqnations. The rate equations can be fnrther subdivided into an atomistic, or microscopic, approach that accounts for individual molecules as they go through the various processes (adsorption, desorption, diffusion, capture, and release) or a phenomenological, or macroscopic, explanation that looks for correlations and the so-called scaling laws over large distances (much larger than the lattice spacing). 

The idea here is that metals can be dissolved most easily if they have been reduced into a fine powder by calcination. The particles that result are so fine that they are almost atomic—quasi atonws. A similar reference to atoms occurs when Sennert discusses the alchemical process of sublimation, whereby a dry substance is vaporized and then recondensed in a sort of still called an alembic. Here Sennert again takes a corpuscularian explanation from Geber and compares it to an outright atomistic one he says that the condensed particles collect on the side of the alembic in the manner of atoms imtar atomoruni) One can see, then, that Sennert in 1611 was fully aware of the advantages of corpuscular explanations, but that he was not yet willing to identify himself with the school... 

Nernst s three seminal contributions of 1888 and 1889 (refs. 5-7) provided for the first time clear, atomistic explanations of, and quantitative expressions for, potential differences across ... 

Rajasekharan and co-workers have investigated united atom and atomistic models of blends of polyethylene with vinyl polymers. They have provided a simple explanation of why isotactic polypropylene and polyethylene are immiscible even though their monomers are so similar. The immiscibility arises from the difference in packing between the branched and linear chains. In a melt the polyethylene molecules prefer to minimize their energy by packing amongst each other rather than packing less efficiently in the blend. 

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