Which of the following molecule has net dipole moment?

Options

A. `C Cl_(4)`
B. `C_(2)H_(2)`
C. `BF_(3)`
D. `NH_(3)`.

Answer

To determine which of the given molecules has a net dipole moment, we will analyze each option step by step.

### Step 1: Analyze CCl4 (Carbon Tetrachloride)
1. **Structure**: The central atom is carbon (C) with four chlorine (Cl) atoms attached.
2. **Valence Electrons**: Carbon has 4 valence electrons, and each chlorine has 7, making a total of 4 single bonds.
3. **Steric Number**: The steric number is 4 (4 sigma bonds, 0 lone pairs).
4. **Hybridization**: The hybridization of carbon is sp³.
5. **Geometry**: The molecular geometry is tetrahedral.
6. **Dipole Moments**: Each C-Cl bond has a dipole moment pointing towards chlorine (more electronegative).
7. **Net Dipole Moment**: The symmetry of the tetrahedral shape means that the dipole moments cancel each other out. Thus, the net dipole moment is zero.

**Conclusion**: CCl4 does not have a net dipole moment.

### Step 2: Analyze C2H2 (Acetylene)
1. **Structure**: The molecule consists of two carbon (C) atoms and two hydrogen (H) atoms.
2. **Valence Electrons**: Each carbon has 4 valence electrons and forms a triple bond with another carbon and a single bond with hydrogen.
3. **Steric Number**: Each carbon has a steric number of 2 (2 sigma bonds, 0 lone pairs).
4. **Hybridization**: The hybridization of carbon is sp.
5. **Geometry**: The molecular geometry is linear.
6. **Dipole Moments**: There is no difference in electronegativity between the two carbon atoms, so the dipole moments from the C-H bonds cancel each other out.
7. **Net Dipole Moment**: The molecule is symmetrical, leading to a net dipole moment of zero.

**Conclusion**: C2H2 does not have a net dipole moment.

### Step 3: Analyze BF3 (Boron Trifluoride)
1. **Structure**: The central atom is boron (B) with three fluorine (F) atoms attached.
2. **Valence Electrons**: Boron has 3 valence electrons, and each fluorine has 7, forming three single bonds.
3. **Steric Number**: The steric number is 3 (3 sigma bonds, 0 lone pairs).
4. **Hybridization**: The hybridization of boron is sp².
5. **Geometry**: The molecular geometry is trigonal planar.
6. **Dipole Moments**: Each B-F bond has a dipole moment pointing towards fluorine.
7. **Net Dipole Moment**: The symmetry of the trigonal planar shape means that the dipole moments cancel each other out. Thus, the net dipole moment is zero.

**Conclusion**: BF3 does not have a net dipole moment.

### Step 4: Analyze NH3 (Ammonia)
1. **Structure**: The central atom is nitrogen (N) with three hydrogen (H) atoms attached and one lone pair.
2. **Valence Electrons**: Nitrogen has 5 valence electrons, forming three single bonds with hydrogen and having one lone pair.
3. **Steric Number**: The steric number is 4 (3 sigma bonds, 1 lone pair).
4. **Hybridization**: The hybridization of nitrogen is sp³.
5. **Geometry**: The molecular geometry is tetrahedral, but the shape is trigonal pyramidal due to the lone pair.
6. **Dipole Moments**: Each N-H bond has a dipole moment pointing towards nitrogen.
7. **Net Dipole Moment**: The lone pair creates an additional dipole moment pointing upwards, resulting in a net dipole moment that is not zero.

**Conclusion**: NH3 has a net dipole moment.

### Final Answer:
The molecule that has a net dipole moment is **D. NH3 (Ammonia)**.

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