Which of these chlorides will have the highest melting point?

Options

A. LiCl
B. NaCl
C. KCl
D. RbCl

Answer

To determine which chloride has the highest melting point among lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), and rubidium chloride (RbCl), we need to consider the factors that affect the melting point of ionic compounds. Here’s a step-by-step solution:

### Step 1: Understand the Factors Affecting Melting Point
The melting point of ionic compounds is influenced primarily by:
1. **Charge of Ions**: Higher charges on the cation or anion lead to stronger electrostatic forces and higher melting points.
2. **Ionic Radii**: Smaller ionic radii result in stronger attractions between ions, leading to higher melting points. Conversely, larger ionic radii result in weaker attractions and lower melting points.

### Step 2: Analyze the Given Chlorides
The chlorides in question are:
- Lithium chloride (LiCl)
- Sodium chloride (NaCl)
- Potassium chloride (KCl)
- Rubidium chloride (RbCl)

### Step 3: Compare the Cations
All the chlorides have the same anion (Cl⁻), but different cations (Li⁺, Na⁺, K⁺, Rb⁺). The order of cation size increases as follows:
- Li⁺ < Na⁺ < K⁺ < Rb⁺

### Step 4: Determine the Melting Point Trend
- **LiCl**: Although Li⁺ is the smallest cation, LiCl exhibits high covalent character due to excessive polarization, which lowers its melting point compared to other chlorides.
- **NaCl**: Na⁺ is larger than Li⁺ but still has a significant charge, leading to a higher melting point.
- **KCl**: K⁺ is larger than Na⁺, resulting in a lower melting point than NaCl.
- **RbCl**: Rb⁺ is the largest cation, leading to the lowest melting point among these chlorides.

### Step 5: Conclusion
Based on the analysis, the order of melting points from highest to lowest is:
1. **NaCl** (highest melting point)
2. KCl
3. RbCl
4. LiCl (lowest melting point due to covalent character)

Thus, the chloride with the highest melting point is **sodium chloride (NaCl)**.

### Final Answer
**Sodium chloride (NaCl) has the highest melting point among the given chlorides.**

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