Question

Which of the following molecules have net dipole moments? For the molecules that are polar, indicate the polarity of each bond and the direction of the net dipole moment of the molecule. a. \(\mathrm{CH}_{2} \mathrm{Cl}_{2}, \mathrm{CHCl}_{3}, \mathrm{CCl}_{4}\) b. \(\mathrm{CO}_{2}, \mathrm{N}_{2} \mathrm{O}\) c. \(\mathrm{PH}_{3}, \mathrm{NH}_{3}\)

Short answer

In summary, the following molecules have net dipole moments: a. \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) with the net dipole moment towards Cl atoms, and \(\mathrm{CHCl}_{3}\) with the net dipole moment towards Cl atoms. b. \(\mathrm{N}_{2} \mathrm{O}\) with the net dipole moment towards the O atom. c. \(\mathrm{PH}_{3}\) with the net dipole moment towards H atoms, and \(\mathrm{NH}_{3}\) with the net dipole moment towards H atoms. The molecules \(\mathrm{CCl}_{4}\) and \(\mathrm{CO}_{2}\) have no net dipole moments due to their symmetric structure.

Step-by-step solution

Determine the Molecular Geometry

For each molecule, determine the geometric structure based on VSEPR theory (Valence Shell Electron Pair Repulsion theory). a. \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\): Tetrahedral, but with two hydrogen atoms making it nonlinear. \(\mathrm{CHCl}_{3}\): Tetrahedral \(\mathrm{CCl}_{4}\): Tetrahedral b. \(\mathrm{CO}_{2}\): Linear \(\mathrm{N}_{2} \mathrm{O}\): Linear c. \(\mathrm{PH}_{3}\): Trigonal pyramidal \(\mathrm{NH}_{3}\): Trigonal pyramidal

Identify Polar Bonds

Identify the polar bonds based on the electronegativity difference between the atoms in the bond. a. \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\): C-H and C-Cl bonds are polar \(\mathrm{CHCl}_{3}\): C-H and C-Cl bonds are polar \(\mathrm{CCl}_{4}\): C-Cl bonds are polar b. \(\mathrm{CO}_{2}\): C-O bonds are polar \(\mathrm{N}_{2} \mathrm{O}\): N-N bond is not polar, N-O bond is polar c. \(\mathrm{PH}_{3}\): P-H bonds are polar \(\mathrm{NH}_{3}\): N-H bonds are polar

Determine Net Dipole Moments

Analyze if the bond dipoles cancel each other out or result in a net dipole moment based on the molecular geometry. a. \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\): The molecule is asymmetric, so the bond dipoles do not cancel, creating a net dipole moment. \(\mathrm{CHCl}_{3}\): The molecule is asymmetric, so the bond dipoles do not cancel, creating a net dipole moment. \(\mathrm{CCl}_{4}\): The molecule is symmetric, so the bond dipoles cancel each other, and there is no net dipole moment. b. \(\mathrm{CO}_{2}\): The molecule is symmetric, so the bond dipoles cancel each other, and there is no net dipole moment. \(\mathrm{N}_{2} \mathrm{O}\): The molecule is asymmetric, so the bond dipoles do not cancel, creating a net dipole moment. c. \(\mathrm{PH}_{3}\): The molecule is asymmetric, so the bond dipoles do not cancel, creating a net dipole moment. \(\mathrm{NH}_{3}\): The molecule is asymmetric, so the bond dipoles do not cancel, creating a net dipole moment.

Indicate the Bond Polarity and Direction of the Net Dipole Moment

Show the polarity of each bond and direction of the net dipole moment for the polar molecules. a. \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\): The C-H bond and C-Cl bond dipoles point toward the more electronegative atoms (Cl and H), and the net dipole moment points in the direction of the Cl atoms. \(\mathrm{CHCl}_{3}\): The C-H bond dipoles point toward H, and the C-Cl bond dipoles point toward Cl. The net dipole moment points in the direction of the Cl atoms. b. \(\mathrm{N}_{2} \mathrm{O}\): The N-O bond dipoles point toward the more electronegative O atom, and the net dipole moment points in the direction of the O atom. c. \(\mathrm{PH}_{3}\): The P-H bond dipoles point toward the more electronegative H atoms, and the net dipole moment points in the direction of the H atoms. \(\mathrm{NH}_{3}\): The N-H bond dipoles point toward the more electronegative H atoms, and the net dipole moment points in the direction of the H atoms.