The favourable factors for the formation of the ionic bond are given below:

⇒Ionization Enthalpy: It is defined as the amount of energy required to remove the most loosely bound electron from an isolated gaseous atom of an element. The lesser the ionization energy, the greater is the ease of the formation of a cation. Alkali metals and alkaline earth metals have low ionization energies and, therefore, they form metals cations very easily.

⇒Electron Affinity: It is defined as the amount of energy released when an electron is added to an isolated gaseous atom of an element. The formation of an anion occurs with the addition of one or more electrons to an atom. The greater the energy released during this process, the easier will be the formation of an anion. Thus, high electron affinity of a non-metals favours the formation of an anion.

⇒Lattice Energy: It is defined as the amount of energy released when cations and anions are brought from infinity to their respective equilibrium sites in the crystal lattice to form one mole of the ionic compound. The higher the magnitude of the lattice energy, the greater is the tendency of the formation of an ionic bond.

Thus, the lower ionization energy of an atom (generally a metal atom), the high electron affinity of another atom (generally a non-metal atom) and a high lattice energy of the compound formed to facilitate the formation of an ionic bond.