A chemical compound that is formed by the transfer of electrons between constituent atoms. For example, sodium (Na) reacts with chlorine (Cl) by sodium losing an electron, leaving it with a positive charge (Na⁺); it is then a cation (positive ion). Chlorine gains an electron, leaving it with a net negative charge (Cl^–); it is then an anion (negative ion). Since opposite charges attract, an ionic bond forms between sodium and chlorine, making the ionic compound NaCl (common salt), which is neutral.