Which of the following is correct order of dipole moment ?

Options

A. `NH_(3) gt NF_(3)`
B. `BeF_(3) gt BCl_(3)`
C. `CF_(4) gt CH_(4)`
D. `XeF_(2) gt XeO_(3)F_(2)`

Answer

To determine the correct order of dipole moments among the given molecules, we need to analyze the molecular geometry and the electronegativity of the atoms involved in each molecule. Here’s a step-by-step solution:

### Step 1: Analyze NH3 (Ammonia)
- **Structure**: NH3 has a trigonal pyramidal shape due to the presence of a lone pair of electrons on nitrogen.
- **Dipole Moment**: The N-H bonds are polar, with nitrogen being more electronegative than hydrogen. The dipole moments of the N-H bonds add up, and the lone pair contributes to a net dipole moment pointing towards the nitrogen.
- **Conclusion**: NH3 has a significant dipole moment.

### Step 2: Analyze NF3 (Nitrogen Trifluoride)
- **Structure**: NF3 also has a trigonal pyramidal shape, similar to NH3.
- **Dipole Moment**: The N-F bonds are polar, with fluorine being more electronegative than nitrogen. However, the dipole moments of the N-F bonds point away from nitrogen, and the lone pair on nitrogen does not contribute effectively to the dipole moment in the same way as in NH3.
- **Conclusion**: NF3 has a lower dipole moment than NH3.

### Step 3: Analyze BEF3 and BCl3
- **Structure**: Both BEF3 and BCl3 have a trigonal planar geometry.
- **Dipole Moment**: In both cases, the dipole moments of the bonds cancel out due to symmetry, resulting in a net dipole moment of zero.
- **Conclusion**: Both BEF3 and BCl3 have zero dipole moments.

### Step 4: Analyze CF4 and CH4
- **Structure**: Both CF4 and CH4 have a tetrahedral shape.
- **Dipole Moment**: CF4 has four C-F bonds that are polar, but due to symmetry, the dipole moments cancel out, resulting in a net dipole moment of zero. In contrast, CH4 has four C-H bonds, which are also polar, but they add up to give a net dipole moment pointing away from the carbon.
- **Conclusion**: CH4 has a dipole moment, while CF4 has zero dipole moment.

### Step 5: Analyze XCF2 and XCO3F2
- **Structure**: XCF2 has a structure with two F atoms and a lone pair on xenon, leading to a net dipole moment of zero due to symmetry. XCO3F2 has a more complex structure with three oxygen atoms and two fluorine atoms, leading to an asymmetrical distribution of dipole moments.
- **Conclusion**: XCO3F2 has a non-zero dipole moment due to its asymmetrical structure.

### Final Conclusion
Based on the analysis, the correct order of dipole moments from highest to lowest is:
1. NH3 (highest)
2. NF3
3. CH4
4. XCO3F2
5. BEF3 = BCl3 = CF4 = XCF2 (lowest, all have zero dipole moment)