Which shows the highest lattice energy ?

Options

A. RbF
B. CsF
C. NaF
D. KF

Answer

To determine which compound shows the highest lattice energy among the given options (NaF, KF, RbF, and CsF), we can follow these steps:

### Step 1: Understand Lattice Energy
Lattice energy is the amount of energy required to separate one mole of an ionic solid into its gaseous constituent ions. It is influenced by two main factors:
- The magnitude of the charges of the ions.
- The distance between the ions, which is related to their ionic radii.

### Step 2: Identify the Factors Affecting Lattice Energy
- Lattice energy is directly proportional to the product of the charges of the cation and anion.
- Lattice energy is inversely proportional to the distance between the ions, which is influenced by their ionic radii.

### Step 3: Analyze the Given Compounds
The compounds given are:
1. NaF (Sodium Fluoride)
2. KF (Potassium Fluoride)
3. RbF (Rubidium Fluoride)
4. CsF (Cesium Fluoride)

All these compounds contain the same anion (F⁻), but different cations (Na⁺, K⁺, Rb⁺, Cs⁺).

### Step 4: Compare the Sizes of Cations
As we move down the group in the periodic table, the size of the cations increases:
- Na⁺ < K⁺ < Rb⁺ < Cs⁺

### Step 5: Determine the Effect on Lattice Energy
Since lattice energy is inversely proportional to the size of the cation:
- Smaller cations will result in higher lattice energy.
- Therefore, Na⁺ (the smallest cation among the options) will lead to the highest lattice energy.

### Step 6: Conclusion
Based on the analysis:
- NaF has the highest lattice energy due to the small size of Na⁺ compared to the other cations.

Thus, the correct answer is **NaF**.