Which molecule does not show zero dipole moment

Options

A. `BF_3`
B. `NH_3`
C. `C Cl_4`
D. `CH_4`

Explanation

To determine which molecule does not show a zero dipole moment, we need to analyze the molecular geometry and the distribution of electronegativity in various molecules. Here’s a step-by-step solution:

### Step 1: Understand Dipole Moment
A dipole moment occurs when there is a separation of charge within a molecule, leading to a positive end and a negative end. The dipole moment is a vector quantity, which means it has both magnitude and direction.

**Hint:** Remember that dipole moments arise from differences in electronegativity between atoms in a molecule.

### Step 2: Analyze BF3 (Boron Trifluoride)
- **Geometry**: BF3 has a trigonal planar geometry.
- **Electronegativity**: Fluorine is more electronegative than boron, so the dipole moments of the three B-F bonds point towards the fluorine atoms.
- **Resultant Dipole Moment**: The three dipole moments cancel each other out due to symmetry, resulting in a net dipole moment of zero.

**Hint:** Symmetrical molecules with identical bonds often have a zero dipole moment.

### Step 3: Analyze NH3 (Ammonia)
- **Geometry**: NH3 has a trigonal pyramidal geometry due to the presence of a lone pair on nitrogen.
- **Electronegativity**: The dipole moments of the N-H bonds point towards the nitrogen atom.
- **Resultant Dipole Moment**: The lone pair pushes the dipole moments upwards, leading to a net dipole moment that is greater than zero.

**Hint:** Lone pairs can affect the symmetry of a molecule, leading to a non-zero dipole moment.

### Step 4: Analyze CCl4 (Carbon Tetrachloride)
- **Geometry**: CCl4 has a tetrahedral geometry.
- **Electronegativity**: Chlorine is more electronegative than carbon, so the dipole moments of the four C-Cl bonds point towards the chlorine atoms.
- **Resultant Dipole Moment**: The four dipole moments cancel each other out due to symmetry, resulting in a net dipole moment of zero.

**Hint:** Like BF3, CCl4 is symmetrical, leading to a cancellation of dipole moments.

### Step 5: Analyze CH4 (Methane)
- **Geometry**: CH4 also has a tetrahedral geometry.
- **Electronegativity**: The C-H bonds are slightly polar, but due to the symmetry, the dipole moments cancel out.
- **Resultant Dipole Moment**: The net dipole moment is zero.

**Hint:** Similar to CCl4, the symmetry in CH4 leads to a cancellation of dipole moments.

### Conclusion
From the analysis, BF3, CCl4, and CH4 all exhibit zero dipole moments due to their symmetrical structures. However, NH3 does not show a zero dipole moment because of its asymmetrical shape and the presence of a lone pair.

**Final Answer:** The molecule that does not show a zero dipole moment is **NH3 (Ammonia)**.