1. A bond between atoms or groups that carry opposite charges; or, in some cases, partial charges.
2. A chemical bond in which one atom loses an electron to form a positive ion and the other atom gains an electron to form a negative ion,
3. A valence bond in which two atoms are kept together by electrostatic forces caused by transferring one or more electrons from one atom to another atom.

A valence is the combining power of atoms or groups measured by the number of electrons the atom or group will receive, give up, or share in forming a compound.