Answer
(i) As the charges of the ions increase, the lattice energy would increase.
(ii) As the sizes of the ions increase, the lattice energy would decrease.
Work Step by Step
The Coulomb's Law: $$E_{el}=\frac{kQ_1Q_2}{d}$$
- $E_{el}$: the electrostatic potential energy between 2 interacting charged bodies
- $k$: Coulomb's law constant
- $Q_1$ and $Q_2$: the charges of 2 interacting charged bodies
- $d$: the distance between these 2 interacting charged bodies
The Coulomb's Law can show the magnitude of attraction among oppositely charged ions in a compound, which eventually defines the magnitude of lattice energy of the compound.
Looking at Coulomb's Law, we see that the magnitude of attraction is directly proportional with the magnitude of charges of the ions and inversely proportional with the distance among them. In other words, the larger the ion charges are and the smaller the distance among the ions is, the larger the attraction among them is and vice versa.
Lattice energy depends on the attraction among the ions: a high lattice energy means a large attraction among the ions in the compound. Therefore, the large ions charges and the small distance among the ions also mean high lattice energy.
Therefore, (i) as the charges of the ions increase, the lattice energy would increase.
(ii) as the sizes of the ions increase, the distance between the ions would increase, and the lattice energy would decrease as a result.
