Most covalent compound among the following

Options

A. LiCl
B. BeO
C. NaCl
D. MgO

Answer

To determine the most covalent compound among the given options (LiCl, BeO, NaCl, MgO), we can use Fajan's rule, which helps us understand the covalent character of ionic compounds based on the size and charge of the cations and anions involved.

### Step-by-Step Solution:

1. **Identify the Cations and Anions**:
- The compounds are:
- LiCl: Cation = Li⁺, Anion = Cl⁻
- BeO: Cation = Be²⁺, Anion = O²⁻
- NaCl: Cation = Na⁺, Anion = Cl⁻
- MgO: Cation = Mg²⁺, Anion = O²⁻

2. **Analyze the Cations**:
- Li⁺ (from LiCl) and Na⁺ (from NaCl) both have a +1 charge.
- Be²⁺ (from BeO) and Mg²⁺ (from MgO) both have a +2 charge.
- Among the cations, Li⁺ and Na⁺ are smaller than Be²⁺ and Mg²⁺ due to their lower charge and position in the periodic table.

3. **Consider the Size of Cations**:
- As we move down a group in the periodic table, atomic size increases. Therefore, Li⁺ is smaller than Na⁺, and Be²⁺ is smaller than Mg²⁺.
- The smaller the cation, the greater the covalent character due to stronger polarization of the anion.

4. **Analyze the Anions**:
- Cl⁻ (from LiCl and NaCl) is larger than O²⁻ (from BeO and MgO).
- Larger anions (like Cl⁻) have less covalent character compared to smaller anions (like O²⁻).

5. **Determine Covalent Character**:
- According to Fajan's rule:
- Covalent character increases with:
- Smaller cation size
- Larger anion size
- Higher charge on the cation
- Be²⁺ has a small size and a +2 charge, which increases its covalent character.
- O²⁻ is also a small anion, which contributes to the covalent character of BeO.

6. **Evaluate Each Compound**:
- **LiCl**: Li⁺ is small, but Cl⁻ is large; overall, it has low covalent character.
- **BeO**: Be²⁺ is small and has a high charge, while O²⁻ is small; this compound has significant covalent character.
- **NaCl**: Na⁺ is larger than Li⁺, and Cl⁻ is large; thus, it has low covalent character.
- **MgO**: Mg²⁺ has a small size and high charge, but O²⁻ is small, leading to less covalent character than BeO.

7. **Conclusion**:
- The compound with the highest covalent character among the given options is **BeO**.

### Final Answer:
The most covalent compound among the following is **BeO**.