# Which of the following has the most exothermic lattice energy: #Ca_3N_2, CaO, SrF_2, Sr_3N_2, Ca_3P_2#?

##### 1 Answer

#### Explanation:

**Lattice energy** is the energy released when oppositely charged ions in the gas phase come together to form a solid.

According to **Coulomb's Law**, the force of attraction between oppositely charged particles is directly proportional to the product of the charges of the particles (

This leads to two principles:

**1. Lattice energy decreases as you move down a group.**

The atomic radius increases as you move down a group.

The force of attraction is inversely proportional to the square of the distance, so lattice energy decreases as the atomic radius increases.

**2. Lattice energy increases as the magnitude of the charge increases.**

The force of attraction is directly proportional to the product of the charges of the particles.

Therefore, lattice energy increases as the charges increase.

**Conclusion:** the salts with the largest ionization energies will be at the top of the Periodic Table and will have ions with the greatest charges.

Let's assemble the ions in a mini-Periodic Table.

The cation with the smallest ionic radius is

The anion with the greatest charge is

Thus, the salt with the most exothermic lattice energy is