Melting point is low for

Options

A. Calcium fluoride
B. Calcium iodide
C. Calcium Chloride
D. Calcium bromide

Answer

To determine which compound has the lowest melting point among calcium fluoride (CaF2), calcium iodide (CaI2), calcium chloride (CaCl2), and calcium bromide (CaBr2), we need to analyze the ionic and covalent character of these compounds based on the properties of their constituent ions.

### Step-by-step Solution:

1. **Identify the Cation and Anions**:
- All compounds have the same cation, which is calcium (Ca²⁺).
- The anions are different:
- CaF2 has F⁻ (fluoride)
- CaCl2 has Cl⁻ (chloride)
- CaBr2 has Br⁻ (bromide)
- CaI2 has I⁻ (iodide)

2. **Analyze the Size of Anions**:
- The size of the anions increases as we move down the group in the periodic table:
- F⁻ < Cl⁻ < Br⁻ < I⁻
- Therefore, I⁻ is the largest anion among the given options.

3. **Determine Covalent and Ionic Character**:
- According to Fajans' rules, smaller cations and larger anions lead to increased covalent character due to polarization.
- Since Ca²⁺ is the same for all, we focus on the anions:
- I⁻ being the largest will be more polarizable, leading to a greater covalent character in CaI2.
- Conversely, F⁻ being the smallest will have the least covalent character.

4. **Relate Ionic Character to Melting Point**:
- Compounds with higher ionic character have stronger ionic bonds and thus higher melting points.
- Conversely, compounds with more covalent character have weaker bonds and lower melting points.

5. **Conclusion**:
- Since CaI2 (calcium iodide) has the highest covalent character due to the large size of I⁻, it will have the lowest ionic character.
- Therefore, calcium iodide will have the lowest melting point among the given compounds.

### Final Answer:
The melting point is low for **calcium iodide (CaI2)**.

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