Based on lattic energy and other considerations, which one of the following alkali metal chloride is expected to have the highest melting point ?

Options

A. LiCI
B. NaCI
C. KCI
D. RbCI

Answer

To determine which alkali metal chloride has the highest melting point based on lattice energy and other considerations, we can follow these steps:

### Step 1: Understand the Concept of Lattice Energy
Lattice energy is the energy released when gaseous ions combine to form an ionic solid. A higher lattice energy typically indicates a stronger ionic bond, which generally leads to a higher melting point.

**Hint:** Remember that lattice energy is influenced by the charges of the ions and the distance between them.

### Step 2: Analyze the Alkali Metals and Their Chlorides
The alkali metals in question are Lithium (Li), Sodium (Na), Potassium (K), and Rubidium (Rb). Their respective chlorides are LiCl, NaCl, KCl, and RbCl.

**Hint:** Consider the size of the alkali metal ions as you analyze their chlorides.

### Step 3: Compare the Sizes of Alkali Metal Ions
As we move down the group from Li to Rb, the size of the alkali metal ions increases. Larger ions lead to a decrease in lattice energy because the distance between the ions increases.

**Hint:** Larger ions result in weaker ionic bonds due to increased distance.

### Step 4: Consider the Nature of the Bonds
Lithium chloride (LiCl) has a significant covalent character due to the small size of the lithium ion, which can polarize the chloride ion. This covalent character reduces the lattice energy compared to NaCl.

**Hint:** Covalent character in ionic compounds can affect their melting points.

### Step 5: Evaluate the Melting Points
- **LiCl**: Lower melting point due to covalent character.
- **NaCl**: Higher melting point due to stronger ionic bonds and higher lattice energy.
- **KCl** and **RbCl**: Even lower melting points due to larger ionic sizes leading to decreased lattice energy.

**Hint:** Compare the melting points based on the strength of ionic bonds.

### Step 6: Conclusion
Based on the analysis, NaCl is expected to have the highest melting point among the given alkali metal chlorides due to its strong ionic bonds and relatively high lattice energy compared to LiCl, KCl, and RbCl.

**Final Answer:** The alkali metal chloride expected to have the highest melting point is **NaCl** (Option B).

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