Concept: Ionic Bond Formation

An ionic bond is formed by the complete transfer of one or more electrons from one atom to another, resulting in the formation of oppositely charged ions (cations and anions) which are then held together by strong electrostatic forces of attraction.

Why (A) is correct:

For an ionic bond to form, one atom must readily lose electrons to become a positively charged ion (cation), and the other atom must readily gain electrons to become a negatively charged ion (anion).

• An atom with a low ionization energy readily loses electrons. Ionization energy is the energy required to remove an electron from a gaseous atom.
• An atom with a high electron affinity readily accepts electrons. Electron affinity is the energy released when an electron is added to a gaseous atom.

Therefore, the combination of an atom that easily loses electrons (low ionization energy) and an atom that easily gains electrons (high electron affinity) is ideal for ionic bond formation.

Option Analysis:

• A) one of them has a low ionization energy and the other a high electron affinity: This condition favors the complete transfer of electrons, leading to the formation of stable ions and thus an ionic bond.
• B) both the atoms have low values of ionization energy: Both atoms would tend to lose electrons, making it difficult for one to accept electrons from the other. This scenario is more conducive to metallic bonding or no bond formation.
• C) both the atoms have high values of ionization energy: Both atoms would strongly resist losing electrons, making electron transfer energetically unfavorable. This condition is more favorable for covalent bond formation (sharing of electrons).
• D) both the atoms have low values of electron affinity: Both atoms would resist gaining electrons, making it difficult for one to accept electrons from the other. This scenario is not conducive to ionic bond formation.

Correct Answer: (A)