Question

The magnitude of the lattice energy of a solid increases if-
A.The ions are large
B.The ions are small
C.The ions are of equal size
D.Charges on the ions are large

Answer 1

Lattice energy is the energy released when the ions of opposite charge in their gas phase come together to form a solid phase. Lattice energy depends on two factors-
(i)Charge of the ions
(ii)Size of the ions

Complete step-by-step answer: The lattice energy is the energy released when ions of gaseous phase combine together to form an ionic solid. Lattice energy is directly proportional to the charge on the ions. So the more the charge of the ions the more will be the lattice energy of that crystal.
$\Rightarrow {\text{L}}{\text{.E}}{\text{.}} \propto {\text{Charge}}$ -- (i)
As the charge of the ion increases, charge density also increases. So the ions form a strong electrostatic force of attraction which results in a stronger bond. So, more energy will be released during formation of lattice structure.
Lattice energy also depends on the size of the ions. Lattice energy is inversely proportional to the size of the ions. So as the size of the ions increases, the lattice energy of the compound decreases.
$\Rightarrow {\text{L}}{\text{.E}}{\text{.}} \propto \dfrac{1}{{{\text{size}}}}$--- (ii)
As the size increases, the charge density gets distributed so there is more distance between the electrons. Due to this the bond is not as strong as before due to which less energy is required to form the lattice structure.
So the magnitude of lattice energy increases if the ions are small in size and charges on the ions are large.

The correct answers are option B and option D.

Note: Lattice energy is important as it helps in predicting the solubility of ionic solids in water.
Ionic compounds having smaller lattice energies are more soluble in water.
Ionic compounds having larger lattice energies are less soluble in water.