ionic bond
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.
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1947 (