Animation of the formation of an ionic bond between a sodium atom and a chlorine atom. Sodium Na has one electron black ball in its outer shell. Chlorine Cl has seven. Atoms are most stable with eight electrons in their outer shells. The lone outer electron on the sodium atom is easily removed due to its low ionisation energy grey inward flash. The electron now purple is readily accepted by the chlorine atom, filling its outer shell, making it more stable grey outward flash. As sodium is now missing one negatively_charged electron, it becomes a positive ion Na+. As chlorine has gained an electron, it becomes a negative ion Cl_. Opposite electric charges attract each other, so the ions move closer, forming a bond outward flash, and creating the compound sodium chloride common salt.