Question

Which of the following factor(s) favours the formation of ionic bonds?
A. The electrostatic attraction between charged ions in the crystal (i.e., lattice energy) should be low.
B. Both atoms should be equal in size.
C. The combination atoms should differ by at least $2.0$ in electronegativity.
D. The cation and anion should have inert gas configuration.

Answer 1

Electrovalency is the formation of electrovalent bond also known as ionic bond; the more ionic the species is, the more will it favour the formation of electrovalent bond. A large size of cation makes it easier to lose electrons. High charges will lead to more electrostatic attraction between cation and anion.

Complete step-by-step answer:
Ionic bond is just a very strong electrostatic force of attraction between cation and anion. Generally a cation is formed by metal because cation is a positively charged species and metals are electropositive in nature, which tends to donate electrons. The anion is formed generally by non metals which have a tendency of gaining electrons are electronegative elements. The ionic bonds are non directional in nature. The favourable condition for the formation of ionic bond is:
Low ionization energy of metal so that it will easily lose electrons to form cation.
High electron affinity of non-metal so as it could accept the electron and form an anion.
Large size cation so that it has less polarizing power.
Small-sized anion so that polarizing could be minimum high lattice energy so as to minimise the energy of crystal for better stability.
Combining cation and anion must be different by equal to or more than $1.7$ electronegativity.
Lattice energy is the amount of energy released when 1 mole of ionic compound is formed from its constituent ions in the gaseous state. If the electrostatic force of attraction between the ions will be low then lesser energy will be released. This will lower the stability of the ionic compound formed and hence option A will not favour the formation of ionic bonds.
For the formation of a good ionic bond the cation should be bigger in size and anion should be smaller in size, hence option B is also incorrect.
The difference of electronegativity between the combining atoms should be $2.0$ so option C is correct.
After losing the electrons the respective elements must reach their stable octet or stable inert gas electron configuration. For example when sodium chloride is formed from Sodium and chlorine, sodium loses one electron and gains Neon like electronic configuration which is an inert gas. The chloride gains 1 electron and becomes argon like electronic configuration so option D is also correct.

Thus, the correct options are option C and D.

Note: Fajan’s rule tells us about the percentage covalent character in ionic bond. It states that the cation having the smaller size and anion will larger size favours the formation of covalent bond. The smaller the cation is the more will be it polarising power due to high charge density. The bigger the anion is the more is its polarizability and it increases the covalent character in an ionic bond.