Heterolysis (chemistry)

Heterolytic fission almost always happens to single bonds; the process usually produces two fragment species.

The energy required to break the bond is called the heterolytic bond dissociation energy, which is similar (but not equivalent) to homolytic bond dissociation energy commonly used to represent the energy value of a bond.

One example of the differences in the energies is the energy required to break a H−H bond

History

The discovery and categorization of heterolytic bond fission was clearly dependent on the discovery and categorization of the chemical bond.

In 1916, chemist Gilbert N. Lewis developed the concept of the electron-pair bond, in which two atoms share one to six electrons, thus forming the single electron bond, a single bond, a double bond, or a triple bond. This became the model for a covalent bond.

In 1932 Linus Pauling first proposed the concept of electronegativity, which also introduced the idea that electrons in a covalent bond may not be shared evenly between the bonded atoms.

However, the ions had been studied before bonds mainly by Svante Arrhenius in his 1884 dissertation. Arrhenius pioneered development of ionic theory and proposed definitions for acids as molecules that produced hydrogen ions, and bases as molecules that produced hydroxide ions.