I. Introduction to Quantum Theory

Also known as quantum mechanics, quantum theory is the mathematical system for describing the behavior of such aspects of physics as light, molecules, atoms and subatomic particles. It is the outgrowth of the quantum concept that all forms of energy are released in discrete units of bundles called quanta. Basically, it is a theory based on using the concepts of the quantum unit to describe the dynamic properties of subatomic particles and the interactions of matter and radiation. It was created under the postulation of a two German physicists: Max Planck, who stated that energy can be emitted or absorbed by matter only in small, discrete units called quanta, and Werner Heisenberg-who said that the position and momentum of a subatomic particle cannot be specified simultaneously. Although quantum mechanics describes the atom purely in terms of mathematical interpretations of observed phenomena, a rough verbal description can be given of what the atom is now thought to be like. Surrounding the nucleus is a series of stationary waves; these waves have crests at certain points, each complete standing wave representing an orbit. The absolute square of the amplitude of the wave at any point is a measure of the probability that an electron will be found at any given time. Thus, an electron can no longer be said to be at any precise point at any given time.

Accomplished

By way of summary, it is perhaps well to list some of the outstanding contributions which quantum theory has made to the understanding of atomic physics. These points are carefully documented and partially derived from research from such references as Encyclopedia Britannica and personal interpretation:

1. The old Bohr theory owes its success to quantum mechanics. the great triumph of the original Bohr version of quantum theory was its ability to explain the spectral frequencies of hydrogenic atoms.

2. Quantum mechanics has provided a procedure for calculating the intensities rather than merely the frequencies of spectral lines.

3. Qualitative explanation of the spectra of nonhydrogenic atoms is now possible. the reason that quantitative precision is not usually possible is simply that when there is more than one electron the wave equation becomes too complicated mathematically to solve exactly.

4. Electron spin has played an important part in understanding of the phenomena of magnetism.

5. A quantum theory of the chemical bond has been formulated. Although chemical processes are so complicated that one cannot hope to calculate accurately from theory the heats of the reactions, still quantum mechanics does enable one to understand the salient features-how valence rules hold as they do and how there are saturated bonds.

6. A quantum theory of the solid state has been formulated. Thanks to quantum mechanics, it can be explained in a general way how atoms are held together in solid bodies. Various properties of solids, such as compressibility, thermal and electrical conductivity, specific heat, etc. also can be explained.

7. Quantum mechanics provides the basis for the interpretation of ionization potentials, capture phenomena and especially questions connected with the shattering of electrons or other particles when they come near atoms or molecules.

8. Numerous phenomena associated with the interaction of radiation with matter were first adequately explained by quantum mechanics. By means of the Kramers formula, a far more profound and realistic description of dispersion is provided than in classical theory.

9. Quantum mechanics provides an explanation of the existence of the positron and antiproton.

10. A quantum electrodynamics, describing many phenomena associated with radiation and the coupling of electrons, has been formulated.

11. Finally, the philosophical implications of quantum theory must not be forgotten. The Heisenberg uncertainty principle, which shows that there is a limit to the precision with which nature can be observed, is particularly important in this respect.