Final answer:
An ionic bond is formed by transferring valence electrons from one atom to another, resulting in cations and anions.
Step-by-step explanation:
An ionic bond is formed by transferring some valence electrons from one atom (usually from a metal atom) to another (usually to a nonmetal atom). The atom that loses an electron becomes a positively charged specie called a cation.
For example, sodium atom Na loses one electron and become Na+, or calcium Ca loses two electrons and becomes Ca²+. The atom that gains an electron becomes a negatively charged specie called an anion. For example, chlorine atom Cl gains one electron and become Cl¯, or oxygen O gains two electrons and becomes 0²-.