Verified by experiments and accepted practically by all theoretical discussions among the scientific communities around the world, there are only two types of chemical interactions that hold atoms together namely the ionic and the covalent bonds. Although it is possible to explain or to describe ionic bond using simple classical ideas simply by electrostatic Coulomb interaction between electrically charged atoms or ions, the same cannot be said for covalent bond.


The explanations and descriptions of covalent bonding were immediately discovered shortly thereafter the final robust reformulation of non-relativistic quantum mechanics (as the final improvement of Bohr’s old quantum mechanics), this was accomplished mainly by Heisenberg and Schrödinger together with Born’s interpretation of quantum mechanics in the middle of the 1920s. Before the discovery of non-relativistic quantum mechanics, scientists were not able to explain why hydrogen atoms form molecular hydrogen, while the noble monoatomic gases like helium could not. The crucial ideas for this discovery are the probability well as the square of the absolute value of the wavefunction and its associated physical variables of meaningful physical terms: the bond dissociation energy, bond length, and the H-H separation distance between two hydrogen atoms. The dissociation energy is defined as the minimum energy that can break the chemical bond between two hydrogen atoms in a hydrogen molecule composed of two hydrogen atoms. The bond length is the distance between atoms that gives the lowest possible energy. The H-H separation distance is defined as the maximum distance between atom where and when they cease to interact thus giving exactly zero bonding energy. The complicated mathematical calculations of this simple idea of what hold atoms together can be found in Michael D. Fayer, Elements of Quantum Mechanics, Chapter 17, New York: Oxford University Press, 2001. Unfortunately, it cannot be sure that this powerful idea of chemical bonding can be used to describe nuclear bonding of deuterons for the theoretical discussion of cold fusion.