Ions form after ionic bonding because of the transfer of electrons between atoms. In ionic bonding, one atom donates an electron to another atom, creating two oppositely charged ions. The positive ion is called a cation, and the negative ion is called an anion. The electrostatic attraction between the cation and the anion holds the ionic compound together.

For example, when sodium and chlorine atoms react to form sodium chloride, the sodium atom donates one electron to the chlorine atom. This creates a sodium ion (Na+) and a chloride ion (Cl-). The sodium ion is positively charged, and the chloride ion is negatively charged. The electrostatic attraction between the sodium ion and the chloride ion holds the sodium chloride compound together.