2. Atoms, Molecules and Moles   Previous PageNext Page
     Bonds Between Atoms

Energy continues to decrease as the atoms come closer and the screening of nuclear charges by electrons increases. If the process is carried too far, however, the electrons are "squeezed out" from between the nuclei, which have come so close together that the repulsion between their positive charges becomes quite strong. The molecule is made less stable.

At some intermediate point, screening by electrons and repulsion of nuclei will balance: The H-H molecule will have the lowest energy and will be most stable. If the nuclei are pushed any closer, nuclear repulsion pushes them back again; if they are pulled apart, electron-pair screening is lost.

This lowest-energy separation, , is the bond length of the H-H bond, and the energy required to pull the molecule apart into isolated atoms again, , is the bond dissociation energy or bond energy. The atoms in a molecule oscillate about this minimum-energy position; thus is the average bond length. In the H-H or , molecule this distance is 0.74 .


G. N. Lewis symbolized an electron-pair bond by two dots for the electrons. It is more common today to represent the bond by a single line connecting the bonded atoms, but you should remember that each such bond consists of a pair of electrons.

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