Chemical fact

The concept of chemical periodicity is central to the study of inorganic chemistry. No other generalization rivals the periodic table of the elements in its ability to systematize and rationalize known chemical facts or to predict new ones and suggest fruitful areas for further study. Chemical periodicity and the periodic table now find their natural interpretation in the detailed electronic structure of the atom indeed, they played a major role at the turn of the century in elucidating the mysterious phenomena of radioactivity and the quantum effects which led ultimately to Bohr s theory of the hydrogen atom. Because of this central position it is perhaps not surprising that innumerable articles and books have been written on the subject since the seminal papers by Mendeleev in 1869, and some 700 forms of the periodic table (classified into 146 different types or subtypes) have been proposed. A brief historical survey of these developments is summarized in the Panel opposite. 

CHEMISTR Y—An Experimental Science presents chemistry as it is today. It does so with emphasis upon the most enjoyable part of chemistry experimentation. Unifying principles are developed, as is appropriate in a modern chemistry course, with the laboratory work providing the basis for this development. When we are familiar with these widely applicable principles we no longer have need for endless memorization of innumerable chemical facts. To see these principles grow out of observations you have made... 

The use of quantum mechanics, or more specifically, orbitals and electronic configurations in teaching general chemistry is now such a widespread trend that it would be utterly futile to try to reverse it. Moreover, orbitals and configurations have been extremely useful in providing a theoretical framework for the unification of a multitude of chemical facts. 

Quantum Mechanics offers the most comprehensive and most successful explanation of many chemical phenomena such as the nature of valency and bonding as well as chemical reactivity. It has also provided a fundamental explanation of the periodic system of the elements which summarizes a vast amount of empirical chemical knowledge. Quantum Mechanics has become increasingly important in the education of chemistry students. The general principles provided by the theory mean that students can now spend less time memorizing chemical facts and more time in actually thinking about chemistry. 

It is the second sequence of Z values shown above that really embodies the periodic system and not the first.11 For all we know electron shells or orbitals may not even exist or may be replaced by some other concept in a future theoiy. But the fact that chemical repetitions occur at Z = 2, 10 18, 36, for example, are chemical facts which will never be superceded. 

NPIRS. 1986. National Pesticide Information Retrieval System (database). Chemical fact sheet for Methyl parathion. U S. Environmental Protection Agency, Office of Pesticide Programs, Washington, DC December, 1986. 

I have touched few items selected in the varied activity of group II not sufficient to give a balanced appraisal of the evolution and of the prospects of the quantum molecular meoiy addressed to interpret chemical facts, but sufficient, I hope, to show that there is here, after more than thirty years of activity, a noticeable momentum, and that in the foreseeable future there will be other important progresses. 

The EPA s Office of Pollution Prevention and Toxics developed Chemical Fact sheets to summarize information on a particular chemical including exposure, environment and human health hazard, environmental fate, regulatory information, and whom to contact for additional information. 

The CrossFire Beilstein database is the world s largest compilation of chemical facts. This database indexes three primary data domains substances, reactions and literature. The substance domain stores structural information with aU associated facts and literature references, including chemical, physical and bioactivity data. The reaction domain details the preparation of substances, enabling scientists to investigate specific reaction pathways with reaction search queries. The literature domain includes citations, titles and abstracts, which are hyperhnked to the substance and reaction domain entries. It contains over 320 million experimental data, over 10 million reactions and data indexed from over 175 journals. 

According to Sect. 3.5 the influencing of an analytical signal by the environment of the experiment (influence factors), i.e. interferences and other stimuli can be estimated either in a way basing on chemical facts (Eq. 3.16a) or in a statistical way (Eq. 3.16b,c). Therefore, two ways are feasible to study the significance of influences as a requirement of a subsequent optimization. 

The total number of atoms on one side of the equation must balance the total number of atoms on the other side. This rule is simply an expression of the well-known chemical fact that atoms are neither created nor destroyed during a chemical reaction. Remember that subscripts and superscripts are labels describing charges and sites and are not counted in evaluating the atom balance. 

Factual — These questions require you to quickly recall important chemical facts. 

The most difficult problem we face in deciding to use a basis of hybrids which reflects the molecular symmetry is how do we choose such a basis in view of the enormous numerical difficulties involved in optimising the non-linear parameters in molecular calculations The real question is are there any rules for this choice, can the optimisation be done (at least approximately) once and for all The chemical evidence is for us — it is the most basic concept of the theory of valence that particular electronic sub-structures tend to be largely environment-independent. How can we select our basis to reflect this chemical fact ... 

Classical structure theory was developed purely from chemical facts, without any help from physics. The theory of resonance was well on its way toward formulation before quantum mechanics was discovered.. . . ... 

Physicists took some pride in what they regarded as the explanatory illumination they were shedding on chemical facts and laws. At the centenary... 

This did not mean there was much sympathy with Brodie s algebraic alternative for molecular models or with Pearson s more sophisticated attempt to introduce the mathematics of ether squirts into chemistry. Nor were chemists ready to give up the periodic table and pictorial theories in the daily work of the laboratory. But, like Robinson, who said that he considered his electronic theory of reaction mechanisms his "most important contribution to knowledge," many chemists considered theory, not chemical fact or chemical production, to be the highest aim of science. 34 And many agreed with Coulson that you cannot have deep theory without mathematics. 

Quantum wave mechanics gave chemistry a new "understanding," but it was an understanding absolutely dependent on purely chemical facts already known. What enabled the theoretician to get the right answer the first time, in a set of calculations, was the experimental facts of chemistry, which, Coulson wrote, "imply certain properties of the solution of the wave equation, so that chemistry could be said to be solving the mathematicians problems and not the other way around."36 So complex are the possible interactions among valence electrons that one must either use an exact mathematical model of a... 

Coulson s generation of quantum theoretical chemists was struck by the fact that the mathematical physics of wave mechanics did not result in fundamental breakthroughs or discoveries in chemistry. As we have seen, Mulliken claimed that his initial work in quantum mechanics "interpreted," rather than "discovered," chemical facts. Alberte Pullman commented in 1970 ... 

Quantum chemistry aims to understand a large variety of chemical facts. In some systems an interesting feature was obtained whose study and whose application can help to reduce the computational effort considerably this is the transferability. Transfer-ability can be interpreted in several ways. The orbitals, on the one hand, may be considered transferable in the case when certain properties of these orbitals are close to each other to a certain extent (Rothenberg, 1971). The transferability of orbitals can be discussed directly on the other hand too. Orbitals of small molecules can be used for constructing the wave-function of related, larger molecules. This can be done with or without further optimizations. In this interpretation the orbitals are transferable if the molecular properties calculated with and without optimizations are close to each other (O Leary et al, 1975). The transferability of orbitals for cyclic hydrocarbons was discussed exhaustively (Edmiston et al., 1963). 

Plastics and Chemical Industries Association. Chemical Fact Sheets, Physical data, chemistry, and production processes of numerous chemical compounds. 

Theophrastus of Eresus was a philosopher of importance in the history of the natural philosophy of the ancients, but he also wrote some works upon subjects more or less closely related to certain chemical facts. These are his brief work upon rocks or minerals, tw Aiftav a treatise... 

The hooks of the Faithful Brothers contain much in the way of chemical facts that shows a knowledge based upon, practical experience in chemical operations. Thus operations of distillation are spoken of in the preparation of waters of roses and violets, and of sharp vinegar, though there is no indication that the methods or apparatus were other than those given for instance by Zosimos in the Greek manuscript of St. Mark. In discussing the metals, many properties are described ... 

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