Electrostatic attraction between oppositely charged ion s in a chemical compound .
Such a bond forms when one or more electron s are transferred from one neutral atom (typically a metal , which becomes a cation ) to another (typically a nonmetallic element or group, which becomes an anion ). The two types of ion are held together by electrostatic forces in a solid that does not comprise neutral molecule s as such; rather, each ion has neighbours of the opposite charge in an ordered overall crystalline structure. When, for example, crystal s of common salt ( sodium chloride , NaCl) are dissolved in water, they dissociate (see dissociation ) into two kinds of ions in equal numbers, sodium cations (Na + ) and chloride anions (Cl - ). See also bonding ; covalent bond .