Which one of the following molecules is not linear ?

Options

A. `BeF_(2)`
B. `BeH_(2)`
C. `CO_(2)`
D. `H_(2)O`

Answer

To determine which molecule among BEF2, BEH2, CO2, and water is not linear, we will analyze the hybridization and molecular geometry of each compound step by step.

### Step 1: Analyze BEF2
1. **Identify the central atom**: Beryllium (Be).
2. **Count valence electrons**: Beryllium has 2 valence electrons.
3. **Count monovalent atoms attached**: There are 2 fluorine (F) atoms attached.
4. **Use the formula for steric number**:
\[ \text{Steric Number} = \frac{(V + M)}{2} \]
where \( V \) is the number of valence electrons and \( M \) is the number of monovalent atoms.
\[ \text{Steric Number} = \frac{(2 + 2)}{2} = 2 \]
5. **Determine hybridization**: A steric number of 2 corresponds to sp hybridization.
6. **Determine geometry**: sp hybridization results in a linear geometry.

### Step 2: Analyze BEH2
1. **Identify the central atom**: Beryllium (Be).
2. **Count valence electrons**: Beryllium has 2 valence electrons.
3. **Count monovalent atoms attached**: There are 2 hydrogen (H) atoms attached.
4. **Use the formula for steric number**:
\[ \text{Steric Number} = \frac{(2 + 2)}{2} = 2 \]
5. **Determine hybridization**: A steric number of 2 corresponds to sp hybridization.
6. **Determine geometry**: sp hybridization results in a linear geometry.

### Step 3: Analyze CO2
1. **Identify the central atom**: Carbon (C).
2. **Count valence electrons**: Carbon has 4 valence electrons.
3. **Count monovalent atoms attached**: There are 2 oxygen (O) atoms attached, but they are divalent.
4. **Use the formula for steric number**:
\[ \text{Steric Number} = \frac{(4 + 0)}{2} = 2 \]
5. **Determine hybridization**: A steric number of 2 corresponds to sp hybridization.
6. **Determine geometry**: sp hybridization results in a linear geometry.

### Step 4: Analyze Water (H2O)
1. **Identify the central atom**: Oxygen (O).
2. **Count valence electrons**: Oxygen has 6 valence electrons.
3. **Count monovalent atoms attached**: There are 2 hydrogen (H) atoms attached.
4. **Use the formula for steric number**:
\[ \text{Steric Number} = \frac{(6 + 2)}{2} = 4 \]
5. **Determine hybridization**: A steric number of 4 corresponds to sp³ hybridization.
6. **Determine geometry**: sp³ hybridization results in a tetrahedral geometry, but the shape is bent (or V-shaped).

### Conclusion
After analyzing all four molecules, we find that:
- BEF2 is linear.
- BEH2 is linear.
- CO2 is linear.
- Water (H2O) is not linear; it has a bent shape.

Thus, the molecule that is not linear is **water (H2O)**.