Quantum or Wave Mechanics

Table 12 and—judged against experiment—superior to others which follow from the quantum or wave-mechanical calculations of Stern-heimer (1954), Das and Wikner (1957), etc. 

Bond Angles and Shapes of Molecules Polar and Nonpolar Molecules Quantum or Wave Mechanics... 

In 1913 Niels Bohr proposed a system of rules that defined a specific set of discrete orbits for the electrons of an atom with a given atomic number. These rules required the electrons to exist only in these orbits, so that they did not radiate energy continuously as in classical electromagnetism. This model was extended first by Sommerfeld and then by Goudsmit and Uhlenbeck. In 1925 Heisenberg, and in 1926 Schrn dinger, proposed a matrix or wave mechanics theory that has developed into quantum mechanics, in which all of these properties are included. In this theory the state of the electron is described by a wave function from which the electron s properties can be deduced. 

Erwin Schrodinger developed an equation to describe the electron in the hydrogen atom as having both wavelike and particle-like behaviour. Solution of the Schrodinger wave equation by application of the so-called quantum mechanics or wave mechanics shows that electronic energy levels within atoms are quantised that is, only certain specific electronic energy levels are allowed. 

The theory, called quantum mechanics or wave mechanics, is now the foundation of the modern description of atomic systems. Mathematically it is quite complex, so that many problems require extensive calculations many others cannot be solved exactly because our mathematical knowledge is insufficient,... 

How do these various atomic orbitals relate to the spatial distribution of electrons in molecules A molecule contains more than one atom (except for molecules like helium or neon), and certain electrons can move between the atoms —this interatomic motion is crucial for holding the molecule together. Fortunately, the spatial localization of electrons in molecules can be described using suitable linear combinations of the spatial distributions of electrons in various atomic orbitals centered about the nuclei involved. In fact, molecular orbital theory is concerned with giving the correct quantum-mechanical, or wave-mechanical, description... 

Quantum mechanics (or wave mechanics) is composed of certain vital principles derived from fundamental assumptions describing the natural phenomena efifeetively. The properties of protons, neutrons and electrons are adequately explained imder quantum mechanics. The electronie features of the molecules responsible for chemical alterations form the basis of drug molecule phenomena. 

Eloborate the rational approach to drug design with regard to Quantum Mechanics (or Wave Mechanics), Molecular Orbital Theory, Molecular Connectivity and Linear Free-Energy Concepts. 

From a theoretical point of view, in the study of atom-atom or atom-molecule collisions one needs to solve the Schrodinger equation, both for nuclear and electronic motions. When the nuclei move at much lower velocities than those of the electrons inside the atoms or molecules, both motions (nuclear and electronic) can be separated via the Born-Oppenheimer approximation. This approach leads to a wave function for each electronic state, which describes the nuclear motion and enables us to calculate the electronic energy as a function of the intemuclear distance, i.e. the potential energy V r). Therefore, V r) can be obtained by solving the electronic Schrodinger equation for each inter-nuclear distance. As a result, the nuclear motion, which we shall see is the way chemical reactions take place, is a dynamical problem that can be solved by using either quantum or classical mechanics. 

Quantum chemistry would become the (necessary) intermediary in the metamorphosis of the current scientist into the scientist of the future, who was idealized as neither a physicist nor a chemist, but a sort of hybrid of the two. Such a scientist would transcend the typical physicist or chemist and needed training in empirical chemistry, in physical chemistry, in metallurgy, in crystal structure, as well as in theoretical physics, including mechanics and electromagnetic theory, and in particular in quantum theory, wave mechanics, the structure of atoms and molecules, in thermodynamics, statistical mechanics, and finally in what Slater called chemical physics. 

Schrodinger s equation launched an entirely new field, called quantum mechanics (or wave mechanics), and began a new era in physics and chemistry. We now refer to the developments in quantum theory from 1913— when Bohr presented his model of the hydrogen atom—to 1926 as old quantum theory. ... 

MaxweU-Boltzmaim particles are distinguishable, and a partition function, or distribution, of these particles can be derived from classical considerations. Real systems exist in which individual particles ate indistinguishable. Eor example, individual electrons in a soHd metal do not maintain positional proximity to specific atoms. These electrons obey Eermi-Ditac statistics (133). In contrast, the quantum effects observed for most normal gases can be correlated with Bose-Einstein statistics (117). The approach to statistical thermodynamics described thus far is referred to as wave mechanics. An equivalent quantum theory is referred to as matrix mechanics (134—136). 

In Schrodinger s wave mechanics (which has been shown4 to be mathematically identical with Heisenberg s quantum mechanics), a conservative Newtonian dynamical system is represented by a wave function or amplitude function [/, which satisfies the partial differential equation... 

Wave mechanics (Schrodinger) or quantum mechanics (Heisenberg)... 

The fundamental equivalence between Schrodinger s wave-mechanical and Heisenberg s matrix-mechanical representation of quantum theory implies that H (or Hm>) may be viewed as a differential operator or a matrix. The latter viewpoint is usually more convenient in the... 

A good deal of this work had no impact in the development of models of molecular structure and the elucidation of reaction mechanisms one reason was Perrin s own coolness to quantum wave mechanics. 108 Another, according to Oxford s Harold Thompson, who studied with Nernst and Fritz Haber, was that researchers like Lecomte "did not know enough chemistry he was a physicist." 109 Perrin, too, approached physical chemistry as a physicist, not as a chemist. He had little real interest or knowledge of organic chemistry. But what made his radiation hypothesis attractive to many chemists was his concern with transition states and the search for a scheme of pathways defining chemical kinetics. 

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