## ionic bond

https://doi.org/10.1351/goldbook.IT07058
The bond between atoms with sharply different electronegativities. In strict terms, an ionic bond refers to the electrostatic attraction experienced between the electric charges of a cation and an anion, in contrast with a purely covalent bond. In practice, it is preferable to consider the amount of ionic character of a bond rather than referring to purely ionic or purely covalent bonds. The relationship was proposed (L. Pauling) for the estimation of ionic character of a bond between atoms A and B: $\text{Amount of ionic character} = 1 - e^{-1/4}\ (\chi _{\text{A}}\,-\,\chi_{\text{B}})$ where χ A and χ B are the Pauling electronegativities of atoms A and B. This type of bonding is realized mostly in solids.
Source:
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1947 (https://doi.org/10.1351/pac199971101919)