Question

On descending the alkali metal group, the lattice enthalpies of both the oxide and peroxide (or superoxide) decreased, because:

• A. Radii of the cations increased
• B. Charges on the cations increased
• C. Charges on the cations decreased
• D. It depends on the charges of the oxides

Hint:

Lattice enthalpy is directly related to ion size and charge; a larger ionic radius leads to weaker lattice enthalpy.

Answer 1

The Correct Option is A

Step 1: Lattice Enthalpy.
Lattice enthalpy is a measure of the strength of the bonds in a solid ionic compound, and it depends on the charges of the ions and the size (radii) of the ions. The greater the charge and smaller the size of the ions, the stronger the lattice enthalpy.

Step 2: Alkali Metal Trends.
As we move down the alkali metal group, the cation radius increases due to the addition of electron shells. This results in a decrease in lattice enthalpy because the larger ions are less strongly attracted to the anions, leading to weaker lattice formation.

Step 3: Conclusion.
The lattice enthalpy decreases as the cation radius increases, which corresponds to option (1).