Mechanism explanation

For example, whichever form of the table is used, an interesting feature emerges The sequence 2,10,18, 36,54, 86 of atomic numbers, in which each period is dosed in the sense of reaching a noble-gas structure, does not appear to have a strictly quantum-mechanical explanation. Although Pauli s brilliant discovery... 

How Good Is the Quantum Mechanical Explanation of the Periodic System ... 

Scerri, E, (1998) How Good is the Quantum Mechanical Explanation of the Periodic Table , Journal of Chemical Education 75, 1384-1385. 

The second law as it left the hands of Carnot required no explanation. On the caloric theory then prevalent, it was a necessary consequence of a hydrodynamical analogy—the mechanical explanation was in fact, as Carnot s words show, the source of the principle. When the caloric theory was thrown down, the analogy and explanation fell with it, and the reconstruction of Carnot s principle by Clausius and Kelvin resulted in a law of experience. 

The question whether atoms exist or not.. . belongs rather to metaphysics. In chemistry we have only to decide whether the assumption of atoms is an hypothesis adapted to the explanation of chemical phenomena. . . [and] whether a further development of the atomic hypothesis promises to advance our knowledge of the mechanisms of chemical phenomena.. .. I rather expect that we shall some day find, for what we now call atoms, a mathematico-mechanical explanation, which will render an account of atomic weight, of atomicity, and of numerous other properties of the so-called atoms. 50... 

Independently of each other, Pauling and Slater worked out a quantum mechanical explanation of the directional valences characteristic of chemical molecules. They did this by proposing directional properties for the p wave functions and for the sp3 wave functions resulting from "hybridization" of electron wave functions, or orbitals.73... 

Traditional theories on chemical combination were based on projecting observable phenomenon at the macroscopic level to the microscopic level. Hence, the mechanical explanations using size and shape persisted well into the 1600s. Alchemical explanations projected human qualities on matter to account for specific reactions and combinations. Substances that combined had a natural attraction or love for one another. Conversely, other substances hated each other and did not combine. 

Apart from occasional ad hoc mechanical explanations, Lemery s theoretical comments are chiefly concerned with the traditional principles. The presence of one of the principles in a mixt body can be inferred from the correspondence between the properties of the mixt and those of the principle. Thus a body which is hard and stable to heat is presumed to owe those properties to the presence of the earthy principle in its composition with little or no oyl or sulphur. The combustibility of a body clearly indicated the presence of the sulphur or oyly principle in its make up. In spite of the compositional language, the function of these principles was rather to rationalize the properties observed than to define the material composition of the various mixts with which the chymist dealt in the laboratory. 

In general the information is quite specific to its own chapter, and little effort is made to describe parallel behavior between one metal and another, for example. Occasional excursions into descriptions of principles or mechanical explanations give what little sense of philosophical unity there is. A closer look at some of his descriptions will give us a truer feeling for the state of chemical understanding and what concepts were there and what were still lacking before the art could become more truly a science. 

When mineral sulfur is sublimed, the condensed sublimate is called flowers of sulphur, which in those days had medicinal uses. This operation is intended only to rarifie the Sulphur, that being rendered more open, it may work the better. Note again the mechanical explanation. 

Here Boerhaave has provided a kind of mechanical explanation of the varying order of affinities of mercury for the other metals through the principle of like attracts like. The alikeness is found in the heaviness of the metal, which is owing to the quantity of the philosophical mercury contained in each metal. 

What he does not seem to realize is that a perfectly good explanation existed for chemical bonding prior to the advent of the quantum mechanical explanation, namely Lewis s theory whereby pairs of electrons form the bonds between the various atoms in a covalently bonded molecule. Although the quantum mechanical theory provides a more fundamental explanation in terms of exchange energy and so on is undeniable but it also retains the notion of pairs of electrons even if this notion is now augmented by the view that electrons have anti-parallel spins within such pairs. 

R. J. Boyd, Nature, 310, 480 (1984). A Quantum Mechanical Explanation for Hund s Multiplicity Rule. 

His major contributions were twofold. First, he convincingly championed chemistry as an important part of the new natural philosophy of the seventeenth century. More precisely, Boyle argued that chemical philosophy and corpuscular philosophy provided important support for one another. We will soon consider the nature of corpuscular philosophy. For now, it is enough to note that it offered mechanical explanations, based on the behavior of corpuscles. These corpuscles might be aggregations, groups, or clumps of atoms, which were in principle divisible. Alternatively, they might simply be individual atoms, which by definition were indivisible. Boyle made chemistry compatible with the new, fashionable, and dominant kind of scientific explanation. His second major contribution, partly borrowed from Starkey, was the development of an experimental metbod m chemistry that made it fit into the new... 

Boyles contributions to chemistry were numerous and significant. He advanced chemical classification a long way, and his category of neutral substances was valuable for an understanding of the chemistry of salts. Making chemistry a respectable part of natural philosophy was of great importance. The experimental method that Boyle devised, with its emphasis on evidence, repeatability, public verification, quantification, and the use of pure materials, was of even greater importance. His mechanical explanations, however, were ultimately sterile. 

Robert Boyle and Isaac Newton wanted to explain the properties of substances in terms of the properties of constituent corpuscles, which might be complex aggregates or else simple atoms. There was no contradiction between this approach and the alchemical ideas that they built into their chemical practice. But although they both advocated mechanical explanations in chemistry, they meant different things by mechanical. 

We have seen that Boyles mechanical explanations were ultimately sterile, although they had their supporters, as did other versions of corpuscular chemistry. These supporters, especially in France and England, argued, as Boyle had done, for providing what were essentially physical explanations for chemical phenomena, based on the shape, size, motion, and arrangement of atoms and groups of atoms. 

Membranes are typically not cleaned due to a drop in salt rejection. This is because in most instances, there is a mechanical explanation for the drop in salt rejection (see Chapter 12.2.2). However, in the case where membrane scaling is responsible for a drop in salt rejection, normalized permeate flow is generally the first indicator of this phenomenon (see Chapter 11.3.1.2)... 

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