Electron models electromagnetic theory

This experiment established the nuclear model of the atom. A key point derived from this is that the electrons circling the nucleus are in fixed stable orbits, just like the planets around the sun. Furthermore, each orbital or shell contains a fixed number of electrons additional electrons are added to the next stable orbital above that which is full. This stable orbital model is a departure from classical electromagnetic theory (which predicts unstable orbitals, in which the electrons spiral into the nucleus and are destroyed), and can only be explained by quantum theory. The fixed numbers for each orbital were determined to be two in the first level, eight in the second level, eight in the third level (but extendible to 18) and so on. Using this simple model, chemists derived the systematic structure of the Periodic Table (see Appendix 5), and began to... 

Some fundamental concepts pertaining to our subject were discussed in earlier chapters. The necessary concepts from electromagnetic theory and radiation-matter interaction were discussed in Chapter 3. A simple framework suitable for treating linear spectroscopy phenomena was described in Sections 9.2 and 9.3. A prototype model for many problems in optical spectroscopy involves two electronic states, ground and excited, and at least two continuous manifolds of states associated with the radiative and nonradiative environments. Such models were discussed in Sections 9.3 and 10.5.2. 

Although shown to have some serious flaws and long since abandoned, the Bohr model laid the groundwork for the more sophisticated theories of atomic structure that are accepted today and introduced the all-important concept that only specific energy states are allowed for an electron in an atom. Like electromagnetic radiation, electrons in atoms are now visualized as having a dual wave/particle nature. 

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. 

These speculations about the ionic, polar, or electronic nature of chemical bonding, which arose largely from solution theory, resulted mostly in static models of the chemical bond or atom structure. In contrast is another tradition, which is more closely identified with ether theory and electrodynamics. This tradition, too, may be associated with Helmholtz, especially by way of his contributions to nineteenth-century theories of a "vortex atom" that would explain chemical affinities as well as the origin of electromagnetism, radiation, and spectral lines. 

The basic theories of physics - classical mechanics and electromagnetism, relativity theory, quantum mechanics, statistical mechanics, quantum electrodynamics - support the theoretical apparatus which is used in molecular sciences. Quantum mechanics plays a particular role in theoretical chemistry, providing the basis for the valence theories which allow to interpret the structure of molecules and for the spectroscopic models employed in the determination of structural information from spectral patterns. Indeed, Quantum Chemistry often appears synonymous with Theoretical Chemistry it will, therefore, constitute a major part of this book series. However, the scope of the series will also include other areas of theoretical chemistry, such as mathematical chemistry (which involves the use of algebra and topology in the analysis of molecular structures and reactions) molecular mechanics, molecular dynamics and chemical thermodynamics, which play an important role in rationalizing the geometric and electronic structures of molecular assemblies and polymers, clusters and crystals surface, interface, solvent and solid-state effects excited-state dynamics, reactive collisions, and chemical reactions. 

It is not possible for conventional electromagnetic models of the electron to explain the observed property of a point charge with an excessively small radial dimension [20]. Nor does the divergence in self-energy of a point charge vanish in quantum field theory where the process of renormalization has been applied to solve the problem. 

Particle groups, like fermions, can also be divided into the leptons (such as the electron) and the hadrons (such as the neutron and proton). The hadrons can interact via the nuclear or strong interaction while the leptons do not. (Both particle types can, however, interact via other forces, such as the electromagnetic force.) Figure 1.4 contains artistic conceptions of the standard model, a theory that describes these fundamental particles and their interactions. Examples of bosons, leptons, hadrons, their charges, and masses are given in Table 1.6. 

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