Which molecule is most polar? CHF3, CF4, CClF3, CCl4
The Correct Answer and Explanation is:
The most polar molecule among CHF₃, CF₄, CClF₃, and CCl₄ is CHF₃ (fluoroform).
Explanation
To determine which molecule is most polar, we need to understand molecular polarity, which is influenced by two main factors:
- Electronegativity differences between atoms in a bond.
- Molecular geometry, which affects how individual bond dipoles add or cancel out.
1. Molecular Shapes and Symmetry
All four molecules are tetrahedral in geometry since the central atom (carbon) forms four single bonds with surrounding atoms.
- CF₄ (carbon tetrafluoride) and CCl₄ (carbon tetrachloride) are symmetrical molecules. All four substituents are the same, so the individual bond dipoles cancel out. Thus, both are non-polar.
- CHF₃ and CClF₃ are asymmetrical, with one different atom among the four substituents. This asymmetry leads to a net dipole moment, making them polar molecules.
2. Electronegativity Considerations
Electronegativity values:
- F (fluorine): 3.98
- Cl (chlorine): 3.16
- H (hydrogen): 2.20
- C (carbon): 2.55
In CHF₃, the C–F bonds are highly polar due to the large electronegativity difference. The single C–H bond is much less polar and does not cancel the strong C–F dipoles, resulting in a strong net dipole.
In CClF₃, the dipole of the lone C–Cl bond partially cancels the dipoles from the three C–F bonds, but because Cl is more electronegative than H, the cancellation is more effective compared to CHF₃, making CClF₃ less polar than CHF₃.
Conclusion
- Most polar: CHF₃, due to its strong C–F dipoles and the low polarity of the C–H bond, which fails to cancel out the fluorine’s pull.
- Least polar (non-polar): CF₄ and CCl₄, due to their perfect symmetry.
- Intermediate: CClF₃, polar but less than CHF₃.
Thus, CHF₃ is the most polar molecule among the four.
