Which of the following does not have a tetrahedral structure ?

Options

A. (a) `BH_4^-`
B. (b) `BH_3`
C. (c) `NH_4^+`
D. (d) `H_2O`

Explanation

To determine which of the given compounds does not have a tetrahedral structure, we will analyze the hybridization of each compound using the formula for hybridization:

\[ H = \frac{1}{2} (V + M - C) \]

Where:
- \( V \) = Valence electrons of the central atom
- \( M \) = Number of monovalent atoms attached to the central atom
- \( C \) = Total charge on the molecule (considering the sign)

Let's analyze each option step by step.

### Step 1: Analyze BH4⁻
1. **Identify the central atom and its valence electrons**: Boron (B) has 3 valence electrons.
2. **Count the number of monovalent atoms**: There are 4 hydrogen atoms attached to boron.
3. **Determine the total charge**: The charge is -1.
4. **Apply the hybridization formula**:
\[ H = \frac{1}{2} (3 + 4 - (-1)) = \frac{1}{2} (3 + 4 + 1) = \frac{1}{2} (8) = 4 \]
- Hybridization: sp³
- Structure: Tetrahedral

### Step 2: Analyze BH3
1. **Identify the central atom and its valence electrons**: Boron (B) has 3 valence electrons.
2. **Count the number of monovalent atoms**: There are 3 hydrogen atoms attached to boron.
3. **Determine the total charge**: The charge is 0.
4. **Apply the hybridization formula**:
\[ H = \frac{1}{2} (3 + 3 - 0) = \frac{1}{2} (6) = 3 \]
- Hybridization: sp²
- Structure: Planar (triangular planar)

### Step 3: Analyze NH4⁺
1. **Identify the central atom and its valence electrons**: Nitrogen (N) has 5 valence electrons.
2. **Count the number of monovalent atoms**: There are 4 hydrogen atoms attached to nitrogen.
3. **Determine the total charge**: The charge is +1.
4. **Apply the hybridization formula**:
\[ H = \frac{1}{2} (5 + 4 - 1) = \frac{1}{2} (8) = 4 \]
- Hybridization: sp³
- Structure: Tetrahedral

### Step 4: Analyze H2O
1. **Identify the central atom and its valence electrons**: Oxygen (O) has 6 valence electrons.
2. **Count the number of monovalent atoms**: There are 2 hydrogen atoms attached to oxygen.
3. **Determine the total charge**: The charge is 0.
4. **Apply the hybridization formula**:
\[ H = \frac{1}{2} (6 + 2 - 0) = \frac{1}{2} (8) = 4 \]
- Hybridization: sp³
- Structure: Tetrahedral (with lone pairs)

### Conclusion
After analyzing all the compounds:
- **BH4⁻**: Tetrahedral
- **BH3**: Planar (triangular planar)
- **NH4⁺**: Tetrahedral
- **H2O**: Tetrahedral

The compound that does not have a tetrahedral structure is **BH3** (Option B).

### Final Answer
**Option B: BH3 does not have a tetrahedral structure.**

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