The correct order of thermal stability of silicon tetrahalides is

Options

A. `SiF_(4) lt SiCl_(4) lt SiBr_(4) lt SiI_(4)`
B. `SiF_(4) gt SiCl_(4) gt SiBr_(4) gt SiI_(4)`
C. `SiF_(4) lt lt SiCl_(4) lt SiBr_(4) lt SiI_(4)`
D. `SiF_(4) lt SiCl_(4) lt SiBr_(4) lt lt SiI_(4)`

Answer

To determine the correct order of thermal stability of silicon tetrahalides (SiF4, SiCl4, SiBr4, and SiI4), we need to analyze the bond strengths of these compounds. The thermal stability of these tetrahalides is directly related to the strength of the Si-X bonds, where X represents the halogen.

### Step-by-Step Solution:

1. **Understanding Thermal Stability**:
- Thermal stability is influenced by bond strength; stronger bonds lead to higher thermal stability.
- Conversely, weaker bonds result in lower thermal stability.

2. **Comparing Bond Strengths**:
- The silicon tetrahalides we are comparing are SiF4, SiCl4, SiBr4, and SiI4.
- The bond strength decreases as we move from SiF4 to SiI4 due to the increasing size of the halogen atoms.

3. **Analyzing SiF4**:
- In SiF4, the Si-F bond is very strong due to the small size of fluorine, which allows for effective overlap of orbitals.
- Additionally, fluorine has a lone pair that can participate in back-bonding with silicon, enhancing bond strength.

4. **Analyzing SiCl4**:
- In SiCl4, the Si-Cl bond is weaker than the Si-F bond because chlorine is larger than fluorine.
- Chlorine also has a lone pair, but the back-bonding is less effective than in SiF4 due to the larger size of the 3P orbital compared to the 2P orbital of fluorine.

5. **Analyzing SiBr4**:
- In SiBr4, the Si-Br bond is even weaker than SiCl4. The size of bromine is larger, leading to a longer bond length and weaker bond strength.
- There is no effective back-bonding in SiBr4 because the size of the orbitals does not allow for significant overlap.

6. **Analyzing SiI4**:
- SiI4 has the weakest Si-I bond due to the large size of iodine, which results in a very long bond length and minimal bond strength.
- Similar to SiBr4, there is no effective back-bonding.

7. **Establishing the Order of Thermal Stability**:
- Based on the analysis of bond strengths, we can establish the order of thermal stability:
- SiF4 > SiCl4 > SiBr4 > SiI4
- Therefore, the correct order of thermal stability of silicon tetrahalides is:
- **SiF4 > SiCl4 > SiBr4 > SiI4**

### Final Answer:
The correct order of thermal stability of silicon tetrahalides is:
**SiF4 > SiCl4 > SiBr4 > SiI4**