When there is a transfer of electrons from one atom to another, and a strong attraction between the oppositely charged atoms, an ionic bond is formed. In an ionic bond, one atom donates one or more electrons to another atom, resulting in the formation of two oppositely charged ions. The positive ion (cation) is formed when an atom loses electrons, while the negative ion (anion) is formed when an atom gains electrons. The electrostatic force of attraction between the positively and negatively charged ions holds the ionic compound together.

For example, in sodium chloride (NaCl), sodium loses one electron to chlorine, resulting in the formation of Na+ and Cl- ions. The strong electrostatic attraction between the Na+ and Cl- ions forms an ionic bond, holding the sodium and chlorine atoms together in a crystalline lattice structure.