by Tarek Musslimani

Created on: October 12, 2010

The understanding of the nature of the chemical bond is a relatively recent development that dates back only to several decades.  Before the understanding of the chemical bond could be achieved there was a need for the understanding of the nature of atomic structure, which was not completely understood at that time.  By the development of quantum mechanics in general, and the Schroedinger equation in particular, the understanding of the atomic nature began to be more understood. 

The complete solution of the Schroedinger equation of the hydrogen atom gave a complete description of its electronic energies and also gave a description of the radial and angular wave functions of this atom.   This achievement paved the road to the understanding of the structure of more complicated atoms with more than one electron in its structure. 

The solution of the Dirac equation for the hydrogen atom uncovered the existence of the electronic spin which is a very fundamental property to the description of the chemical bond.  Also the principle of exclusion by Pauli led to the understanding that no more than two electrons with opposite spin could occupy the same orbital at the same time. 

The functions of the hydrogen atom, as obtained from the solution of the Schroedinger equation for this atom, were used for a long period of time to describe the orbitals of many electrons atoms by giving the many electrons atom orbital functions that are hydrogenlike wave functions.  The solution of the Schroedinger equation for the hydrogen atom gave, as one of its many results, quantum numbers that designate the energy levels of the electronic levels in the atom.  This is in addition to describing the various orbitals shape, energy and symmetry by other quantum numbers that are also used for other atoms.  These quantum numbers also gave the amount of degeneracy of the orbital levels in the hydrogen atom.  For example p orbital in the hydrogen atom is triply degenerate while d orbitals are five degenerate orbitals. 

All these results contributed to the attempts to understand how chemical bonds occur based on the quantum mechanical data that were obtained for the hydrogen atom.  An orbital is a wave function that is obtained by the solution of the radial part of the Schroedinger equation of the hydrogen atom.  This orbital describes the movement

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