3.14 Bond Strengths
The strength of a chemical bond is measured by its dissociation energy, D, the
energy required to separate the bonded atoms. On a plot of the potential energy of
a diatomic molecule as a function of the internuclear distance, the dissociation
energy is the distance between the bottom of the energy well and the energy of the
separated atoms (FIG. 3.15). The bond breaking is homolytic, which means that
each atom retains one of the electrons from the bond. An example is
H¬Cl(g) ∫B # H(g) # Cl(g)
A high dissociation energy indicates a deep potential energy well and therefore a
strong bond that requires a lot of energy to break. The strongest known bond between
two nonmetal atoms is the triple bond in carbon monoxide, for which the dissociation
energy is 1062 kJmol1. One of the weakest bonds is that between the iodine atoms
in molecular iodine, for which the dissociation energy is only 139 kJmol1.
The strength of a bond between two atoms is measured by its dissociation
energy: the greater the dissociation energy, the stronger the bond.