Chemical bonds Heisenberg uncertainty principle

In the 1920s it was found that electrons do not behave like macroscopic objects that are governed by Newton s laws of motion rather, they obey the laws of quantum mechanics. The application of these laws to atoms and molecules gave rise to orbital-based models of chemical bonding. In Chapter 3 we discuss some of the basic ideas of quantum mechanics, particularly the Pauli principle, the Heisenberg uncertainty principle, and the concept of electronic charge distribution, and we give a brief review of orbital-based models and modem ab initio calculations based on them. 

Today, a technique called transition state spectroscopy that uses lasers with pulse widths around 10 fsec facilitates the detection of transient species with extronely short lifetimes. In this time interval, a bond in its fundamental vibration covers a distance of only 2X10" m. As such, this technique enables one to obtain a sequence of images of vibrational motion of a chemical bond in the act of breaking. However, it is worth remembering that owing to the Heisenberg uncertainty principle ... 

The structure of atoms is known to us in great detail down to the fact that isotopes are not totally equal to the major form of an element. Heavier isotopes react slower in enzyme-catalyzed reactions but they form stronger bonds. No uncertainty is needed for that aspect of our world. Heisenbergs Principle does not pertain to the power fields created by the atomic nuclear structure, but rather to the position of the electrons within these power fields. For the macroscopic world and its chemical basis the position of the power fields (orbitals) is important, and these positions allow carbon, very precisely and very predictably, to give rise to four bonds (or two double bonds as in CO2 or a triple and a single bond as in cyanate) that are stable under a variety of conditions and which allow carbon to form the many and varied polymers that form the skeleton of life. Chemistry does not suffer uncertainty neuroses. 

Heisenberg, Werner P. (1901-1976). A native of Germany, Heisenberg received his doctorate from the University of Munich in 1923, after which he was closely associated for several years with Niels Bohr in Copenhagen. He was awarded the Nobel Prize in physics in 1932 for his brilliant work in quantum mechanics. In 1946, he became director of the Max Planck Institute. His notable contributions to theoretical physics, best known of which was the uncertainty principle, imparted new impetus to nuclear physics and made possible a better understanding of atomic structure and chemical bonding. 

Schrodinger developed the ideas of quantum (wave) mechanics in 1925. It was then applied to determine atomic and molecular structure. The idea of covalent bonding between two atoms based on the sharing of electron pairs was proposed by Lewis in 1916. The Lewis model (of dots and crosses to represent electrons) is still relevant and useful, but the quantum mechanical model (Chapters 2 and 12), incorporating wave-particle duality, Pauli s exclusion principle and Heisenberg s uncertainty principle, gives a deeper understanding of chemical bonds. 

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