Question

How many of the following molecules are polar? $PCl_5(g), SF_6, BF_3, XeF_2, XeO_3$, , , , , .

Answer 1

6

Answer 2

To determine if a molecule is polar, we need to consider its molecular geometry and the polarity of its individual bonds. A molecule is polar if it has a net dipole moment, which occurs when polar bonds are present and their dipoles do not cancel out due to the molecular geometry.

Let's analyze each molecule:

1. $PCl_5(g)$:

   • Geometry: Trigonal bipyramidal.
   • Bond polarity: P-Cl bonds are polar.
   • Symmetry: The molecule is highly symmetrical. The three equatorial P-Cl bond dipoles cancel each other, and the two axial P-Cl bond dipoles cancel each other.
   • Net dipole moment: Zero.
   • Polarity: Nonpolar.

2. $SF_6$:

   • Geometry: Octahedral.
   • Bond polarity: S-F bonds are polar.
   • Symmetry: The molecule is highly symmetrical. All S-F bond dipoles cancel out.
   • Net dipole moment: Zero.
   • Polarity: Nonpolar.

3. $BF_3$:

   • Geometry: Trigonal planar.
   • Bond polarity: B-F bonds are polar.
   • Symmetry: The molecule is highly symmetrical. The three B-F bond dipoles cancel out.
   • Net dipole moment: Zero.
   • Polarity: Nonpolar.

4. $XeF_2$:

   • Geometry: Linear (due to 3 lone pairs in equatorial positions and 2 bonding pairs in axial positions).
   • Bond polarity: Xe-F bonds are polar.
   • Symmetry: The two Xe-F bond dipoles are equal in magnitude and opposite in direction, so they cancel out.
   • Net dipole moment: Zero.
   • Polarity: Nonpolar.

5. $XeO_3$:

   • Geometry: Trigonal pyramidal (due to one lone pair and three Xe=O double bonds).
   • Bond polarity: Xe=O bonds are polar.
   • Symmetry: The molecule is asymmetrical due to the lone pair and the pyramidal shape. The bond dipoles do not cancel out.
   • Net dipole moment: Non-zero.
   • Polarity: Polar.

6. Benzene (C6H6):

   • Geometry: Planar hexagonal.
   • Bond polarity: C-C and C-H bonds are essentially nonpolar or have very small dipoles.
   • Symmetry: The molecule is highly symmetrical.
   • Net dipole moment: Zero.
   • Polarity: Nonpolar.

7. Aniline (C6H5NH2):

   • Structure: Benzene ring with an amino (-NH2) group.
   • Bond polarity: C-N and N-H bonds are polar. The amino group itself is pyramidal and has a dipole moment.
   • Symmetry: The presence of the polar -NH2 group breaks the symmetry of the benzene ring.
   • Net dipole moment: Non-zero.
   • Polarity: Polar.

8. p-Chlorophenol (C6H4ClOH):

   • Structure: Benzene ring with -Cl and -OH groups at para positions.
   • Bond polarity: C-Cl, C-O, and O-H bonds are polar. Both -Cl and -OH groups have significant dipole moments.
   • Symmetry: Although the groups are at para positions, their individual dipole moments are not equal in magnitude, nor do they perfectly cancel out in a vector sum.
   • Net dipole moment: Non-zero.
   • Polarity: Polar.

9. p-Nitroaniline (C6H4NH2NO2):

   • Structure: Benzene ring with -NH2 and -NO2 groups at para positions.
   • Bond polarity: Both -NH2 and -NO2 groups are highly polar. The -NH2 group is electron-donating, and the -NO2 group is strongly electron-withdrawing.
   • Symmetry: The dipole moments of these groups largely align along the axis through the para positions, and their effects are additive, leading to a significant net dipole.
   • Net dipole moment: Non-zero.
   • Polarity: Polar.

10. Pyrrole:

    • Structure: Five-membered heterocyclic aromatic ring with a nitrogen atom (N-H).
    • Bond polarity: C-N and N-H bonds are polar. The nitrogen atom has a lone pair.
    • Symmetry: The molecule is not symmetrical enough for all bond dipoles to cancel.
    • Net dipole moment: Non-zero.
    • Polarity: Polar.

11. Furan:

    • Structure: Five-membered heterocyclic aromatic ring with an oxygen atom.
    • Bond polarity: C-O bonds are polar. The oxygen atom has lone pairs.
    • Symmetry: The molecule is not symmetrical enough for all bond dipoles to cancel.
    • Net dipole moment: Non-zero.
    • Polarity: Polar.

Counting the polar molecules:

1. $XeO_3$
2. Aniline
3. p-Chlorophenol
4. p-Nitroaniline
5. Pyrrole
6. Furan

There are 6 polar molecules in the given list.