Download PDF The Nature of the Chemical Bond, Review 2 (Pauling, Linus). To have a book upon your shelf by Linus Pauling is important. But. i t is far mmo. Linus Pauling, The chemical bond. HOME · Linus Download PDF This is an abridged version of-the author's famous work The Nature of the Chemical Bond. The nature of the chemical bond and the structure of molecules and crystals: an introduction to modern structural by: Pauling, Linus, DOWNLOAD OPTIONS Borrow this book to access EPUB and PDF files.
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The Nature of the Chemical Bond -- Linus Pauling - Download as PDF File .pdf), Text File .txt) or read online. The Nature of the Chemical Bond is a paper. The Nature of the Chemical Bond is a paper written by linus pauling in which he describes the quantum mechanical nature. Click here if your download doesn"t start automatically Download and Read Free Online The Nature of the Chemical Bond Linus Pauling The Nature of the Chemical Bond by Linus Pauling Free PDF d0wnl0ad, audio books, books to read.
Although electrons of one atom repel electrons of another, the repulsion is relatively small. So is the repulsion between atomic nuclei.
Various theories regarding chemical bonds have been proposed over the past years, during which our interpretation of the world has also changed. Some old concepts such as Lewis dot structure and valency are still rather useful in our understanding of the chemical properties of atoms and molecules, and new concepts involving quantum mechanics of chemical bonding interpret modern observations very well. While reading this page, you learn new concepts such as bond length, bond energy, bond order, covalent bond, ionic bond, polar and non-polar bond etc.
These concepts help you understand the material world at the molecular level. The attraction force between ions is called ionic bonding. Metals such as sodium, copper, gold, iron etc. Electrons in these solids move freely throughout the entire solid, and the forces holding atoms together are called metallic bonds. To some extent, metals are ions submerged in electrons. A Brief Past on Chemical Bond Concepts Various concepts or theories have been proposed to explain the formation of compounds.
In particular, chemical bonds were proposed to explain why and how one element reacted with another element. In , E. Frankland proposed the concept of valence. He suggested that each element formed compounds with definite amounts of other elements due to a valence connection. He utilized X-ray crystallography broadly and was constantly on the lookout for new techniques. It was similar to X-ray crystallography, but there were two major differences. It used electrons rather than X-rays and the target was not a crystal but a gaseous sample in which the molecules had no well-defined order in their mutual arrangements.
One of the great advantages of using electrons was the very high intensity of the interaction between electrons and molecules. Thus, the duration of the required interaction was measured in minutes rather than many hours as with X-rays.
The other important advantage was that in the gaseous sample the molecules were by themselves and their structures were not impacted by the closeness of their neighbors. For the X-ray technique, the molecules were required to be able to form a crystal in the first place, and there was no such requirement for using the electron diffraction technique.
The structures determined by the new technique depended only by the molecule itself and not by the way they were arranged relative to each other as was the case in the crystal.
Other limitations of the new technique, however, have restricted it from becoming so widely used as X-ray crystallography, which truly has been the preeminent tool for uncovering the structures of biopolymers. Mark even supplied him with the blueprints of his apparatus. Pauling not only introduced the gas-phase electron diffraction technique quickly in the United States, but he and his student, Lawrence Brockway further developed it. They added a mathematical step to handling the experimental data that made it possible to extract structural information in a graphically direct and attractive way from the probability density distribution of the internuclear distances in the molecule usually it is referred to as the radial distribution curve, which is a misnomer.
Pauling Fig. He then worked out a theoretical technique based on quantum mechanics, but simple enough for a broad circle of chemists, to describe molecular structures. It was called the valence-bond or VB theory and it was one of the two major theoretical approaches developed over the decades. The other is the molecular orbital or MO theory.
The Nature of the Chemical Bond and the Structure of Molecules and Crystals
The VB theory builds the molecules from individual atoms linked by electron-pair bonds. For chemists, the VB theory appealed as more straightforward, alas, it did not stand well the test of time. The MO theory has proved more amenable to computations, which itself has become a major thrust in modern structural chemistry.
However, for a long time the VB theory dominated the field. This did not mean that each structure in such a set would be considered as present individually, but that the sum of these resonating structures represented the emerging structure better than any other description at the time. It needs to be stressed that what the resonance theory provides is merely a model, an approach, rather than a unique reflection of reality. There were proponents and opponents of the theory as is the case with most theories.
Yet the resonance theory proved to be eminently useful for Linus Pauling—who was one of its initiators—in his quest for the protein structure. It happened so that this theory showed him the way and brought him a resounding victory over his competitors who lacked this tool and could not arrive at the right solution.
Pauling was advancing in a systematic manner in his quest for building up structural chemistry. Among the organic molecules he often observed structures in which the lengths of the bonds between atoms were intermediate between single bonds and double bonds, so the theory of resonance came in handy in their understanding and description.
Today, chemists no longer tend to think in terms of purely single bonds and double bonds, or triple bonds for that matter, and, accordingly, the utility of the resonance theory has largely disappeared, but in the s it was considered to be of great help. As Pauling was learning more and more about the structures of relatively simple molecules, in the mids, it occurred to him that he might as well make an attempt to learn about larger systems.
He was aware of the importance of biopolymers and that the understanding of their structures might be a step toward understanding biological processes. Proteins were an obvious choice, because they were the most important biopolymers.
At that time nucleic acids were already known, and their building blocks, the nucleotides, had been identified, but the nucleic acids were not considered to be of great significance.
There was a hypothesis by Phoebus Levene about the tetranucleotide structure that was based on an erroneous observation that the four nucleotides in nucleic acid were present in equal amounts [ 2 ].
Hence, the nucleic acids were thought to be dull, uninteresting molecules, not capable of carrying any great amount of information. When Pauling started thinking about protein structures, the first protein to attract his attention was hemoglobin, which is the vehicle of carrying oxygen in our organism.
At the end of the s, Gilbert Adair in Cambridge, UK, showed that the hemoglobin molecule consists of four units each with an iron atom, and each iron could bind an oxygen atom.
Pauling formulated a theory about the oxygen uptake of hemoglobin and the structural features of this molecule related to its function of disposing of and taking up oxygen. His interest in protein structures was further whetted when a visiting scientist and protein specialist, Alfred Mirsky of the Rockefeller Institute, spent the academic year — in his laboratory.
They jointly studied the phenomenon of denaturation of proteins by heat or chemical substances, and formulated a theory about it. In this theory, they described the native protein as having a regularly folded structure in which hydrogen bonds provided the stability of the structure. Hydrogen bonding was a recently discovered phenomenon; it was becoming recognized as a crucial mode of interaction in chemical structures and especially in those of biological importance.
In retrospect, it was a pivotal discovery, but its significance emerged only gradually over the years.
For many biological molecules it is the hydrogen bonds that keep their different parts together. Pauling postulated that the subsequent amino acid units are linked to each other in the folded protein molecule not only by the normal peptide bond but also by hydrogen bonding that is facilitated by the folding of the protein, which brings the participating atoms sufficiently close to each other for such interactions. By the time Pauling became engaged in this research it had been established from rudimentary X-ray diffraction patterns that there might be two principal types of protein structure.
The Nature of the Chemical Bond -- Linus Pauling
Keratin fibers, such as hair, horn, porcupine quill, and fingernail belonged to one, and silk to the other.
The foremost British crystallographer of fibers, William T. Astbury showed in the early s that the diffraction pattern of hair underwent changes when it was stretched. He called the one producing the normal pattern alpha keratin and the other, which was similar to the pattern from silk, beta keratin. In , Pauling set out to determine the structure of alpha keratin.
He did not just want to rely on a single source of information. He planned to use all his accumulated knowledge in structural chemistry and find the best model that would make sense on this background and would be compatible with the X-ray diffraction pattern. There was one piece of information from X-ray diffraction that seemed to be a good point of reference and that was the structural unit—whatever it would be—along the axis of the protein molecules repeated at the distance of 5.
He also knew the dimensions of the peptide group, that is, the characteristic sizes of the group linking the amino acids to each other in the protein chain. The C—N bond in the peptide linkage was not simply a single bond, but it was not a purely double bond either.
From the accumulated structural information he also knew that the bonds around a double bond are all in the same plane. This was a very important piece of information because rather than taking into account all kinds of rotational forms with respect to the peptide bond, he could assume that it was a planar configuration.
This assumption greatly reduced the number of possible models he had to consider for describing the structure of alpha keratin. Nonetheless, at this time Pauling was unable to find a model that would fit the X-ray diffraction pattern and he postponed further study on protein structures. During the ensuing years Pauling and his newly arrived associate, Robert Corey, an expert in X-ray crystallography, carried out a large amount of experimental work determining the structures of individual amino acids and simple peptides.
The study was interrupted by World War II, but continued vigorously upon its conclusion. Stoner, Phil. I n such cases the higher order perturbation energies are to be compared with the multiplet separation in the above criterion. In linear molecules only the component of orbital momentum normal to the figure axis is destroyed, that along the figure axis being retained. In non-linear molecules with strong interatomic interactions the concept of orbital angular momentum loses its significance.
The rare-earth ions owe their magnetic moments to an incompleted 4f subshell, which lies within an outer shell of 5s and 5p electrons, and is thus protected from strong perturbations by surrounding atoms. As a consequence the orbital magnetic moment is not destroyed, and the ion is not affected by its environment.
But in the iron-group ions and other transition-group ions the incompleted subshell is the outermost one. Hence it is not surprising that the solvent molecules or the surrounding atoms or ions in a complex ion or a crystal interact sufficiently strongly with these atoms or ions to destroy, in whole, or in part, the orbital magnetic moment, leaving the spin moment, with perhaps a small contribution from the orbital moment in border-line cases.
We can state with certainty that the formation of electron-pair bonds will destroy the orbital moment. This greatly simplifies the theory of the magnetic moments of molecules and complex ions. The factor 2 is the g-factor for electron spin. The comparison of calculated and observed values is given in Table I. Bose, 2. Physik, 43, Bose suggested that perhaps S could in some cases exceed the maximum value allowed by Pauli's principle, bht the obviously correct explanation is that the perturbing effect of surrounding atoms is not sufficient completely to destroy the L moment.
Hence the observed moment should lie between ,US and Y J , which it does in every case. Since the interaction is not strong enough to destroy the L moment, we conclude that in aqueous solution and in some crystalline salts the atoms44 Fe", CoIII, Co'', Ni" and Cu" do not form strong electron-pair bonds with H20, C1, or certain other atoms, the bonds instead being ion-dipole or ionic bonds.
The formation of a stable coordination compound involving the four tetrahedral sp3 eigenfunctions might decrease the L contribution appreciably.But despite Noyes's wishes, Millikan refused to make Pauling chair of the division.
Theirs would be a deep, lifelong love.
Frequently bought together
Pauling became engaged in the determination of the structure of many inorganic and organic molecules and amassed a large amount of information about them during the ensuing decade. Their magnitude is in simple proportion to the charge difference. The essential first step in understanding chemical phenomena was to establish the atomic arrangements in the substances of interest. This young firebrand had decided to throw out any visualizable ideas of the atom at all and work instead with pure mathematics to explain the way atoms behaved.
This important step forward won him Sommerfeld's admiration and publication in the prestigious British journal Proceedings of the Royal Society. Pauling not only introduced the gas-phase electron diffraction technique quickly in the United States, but he and his student, Lawrence Brockway further developed it. This triumph is apparent even in the slimmer volume under review and makes this book a must for all undergraduates.
It paid well, and Linus enjoyed camping out with the road crews for weeks at a time, learning about surveying and laughing at the workers' sometimes off-color jokes.
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