Bonded by attraction of opposites — one gives, one receives, and the pull between them is the bond.
Greek ion (going), the neuter present participle of ienai (to go), coined in 1834 for the charged particles that migrate toward an electrode; the ionic bond is named for that migration, the pull of opposite charges toward each other.
One gives, one receives, and the pull between the two unequal halves is the whole bond — nothing shared evenly here.