Question

Which of the following is favourable condition for the formation of ionic bond ?

• A. Low ionization enthalpy of metal and low negative value of electron gain enthalpy of non metal.
• B. Low ionization enthalpy of metal and high negative value of electron gain enthalpy of non metal.
• C. High ionization enthalpy of metal and high negative value of electron gain enthalpy of non metal.
• D. High ionization enthalpy of metal and low negative value of electron gain enthalpy of non metal.

Hint:

An ionic bond forms easily when the metal loses electrons easily and the non-metal gains them with a large release of energy.

Answer 1

The Correct Option is B

Step 1: Energy view
Think of the energy cost and the energy gain of forming ions. Ionic bonding is favoured when the total cost is small and the total gain is large.

Step 2: Cost side
The cost is the ionization enthalpy of the metal. We want it low.

Step 3: Gain side
The gain is the energy released when the non-metal accepts an electron, a highly negative electron gain enthalpy. We want it as negative as possible. Lattice energy adds to the gain.

Step 4: Match with options
Only "low ionization enthalpy plus highly negative electron gain enthalpy" satisfies both wishes. The other three pair a bad factor with a good one, or two bad ones, so they hinder ion formation.

Final Answer:
Option (B) combines both favourable factors. This is option (B). \[ \boxed{\text{(B) }\text{Low IE of metal, high negative } \Delta_{eg}H \text{ of non-metal}} \]