CaO and NaCI have the same crystal structure and approximately the same ionic radii. If U is the lattice energy of NaCl, the approximate lattice energy of CaO is

Options

A. a. `U//2 `
B. b. ` U `
C. c. `2U`
D. d. `4U `

Answer

D

Explanation

Lattice energy `=(q_(1)q_(2))/(r^(2))` where `q_(1) and q_(2)` are charges on ions and r is the distance between them. Since interionic distances in CaO and NaCl are similar, (larger cation has smaller anion and vice versa) therefore, r is almost the same. Therefore, lattice energy depends only on charge. Since the magnitude of charge on `Na^(+) and Cl^(-)` ions is unity and that on `Ca^(2+) and O^(2-)`ions is 2 cach, therefore, the lattice energy of CaO is four times the lattice energy of NaCl, i.c.,4l.