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Molecules


Contents

Quantum Theory, Blackbody Radiation
Correspondence Principle
Uncertainty Principle
Complemetarity Principle
Exclusion Principle
Path Integral, Transition to Qunatum Theory
First Quantization, Schrodinger Equation
Quantum Interpretations
Hydrogen Atom
Covalent Bond, Hydrogen Molecule
Ionic Bond, Atomic Shells
Hydrogen Bond, Molecular Orbital
van der Waals Force, Dipole-Dipole Interaction
Physical Chemistry
Inorganic Chemistry
Organic Chemistry
Soft Matter
Nano-technology
The Future of Chemistry

Quantum Theory, Blackbody Radiation

Molecules are small objects not susceptible of direct observation even under the most powerful microscope. However, their properties can be deduced indirectly from experiments. These objects are different on the conceptual level as well. Classical physics can no longer offer a consistent description. It is replaced by quantum theory, which describes the objects only in term of probability, energy levels, and other quantum numbers. A well-defined orbit such as the path of a planet around the Sun becomes the probability of finding the object at a certain location in the microscopic world. Thus, all the illustrations related to these objects would be just a schematic diagram conveying some ideas, they should never be taken literally as the real thing.

Blackbody Radiation Historically, the quantum theory began with the attempt to account for the discrepancy between the theoretical and observational blackbody radiation. The classical theory of Rayleigh-Jeans failed to fit the observation of the radiation energy distribution from a blackbody at high frequency. In searching for a modification that would reduce the contribution of the high frequencies to the energy, Planck was led to make an assumption: The energy of the radiation with frequency is restricted to integral multiples of a basic unit hv (a quantum), i.e., E = nh where h = 6.625x10-27 erg-sec is the Planck constant and n is an integer. With this assumption, Planck obtained an exact fit to the observed distribution of radiation energy. According to classical theory, electromagnetic radiation is a wave phenomenon. The Planck's assumption endows a particle aspect to the same entity. Such wave-particle duality requires radical changes in the fundamental concepts of the properties of matter and energy. An introduction on the subject of "wave" can be found in the special topic on Wave, Sound, and Music.

Figure 12-01 Blackbody Radiation

See a concise overview of the Quantum Theory, and a more advanced level of the Quantum Theory.

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