molecule polarity - fix (M9Q2)

7) Is the Cl2BBCl2 molecule polar or nonpolar?

nonpolar

4) Determine the electron-pair geometry (EPG) and molecular geometry (MG) for each of the following molecules. Which of the following molecules have dipole moments? a) CS2 b) SeS2 c) CCl2F2 (C is the central atom) d) PCl3 (P is the central atom) e) ClNO (N is the central atom)

(a) CS2: EPG = linear, MG = linear, has nonpolar bonds, no dipole moment (b)SeS2: EPG = trigonal planar, MG = bent, has nonpolar bonds, no dipole moment (c) CCl2F2: EPG = tetrahedral, MG = tetrahedral, has polar bonds, has dipole moment (C-F bonds are more polar than C-Cl bonds) (d) PCl3: EPG = tetrahedral, MG = trigonal pyramidal, has polar bonds, has dipole moment (e) ClNO: EPG = trigonal planar, MG = bent, has polar bonds, has dipole moment

2) Determine the electron-pair geometry (EPG) and molecular geometry (MG) for each of the following molecules and ions. Which of these molecules and ions contain polar bonds? Which of these molecules and ions have dipole moments? a) H3O+ b)PCl4− c) SnCl3− d) BrCl4− e) ICl3 f) XeF4 g) SF2

(a) H3O+: EPG = tetrahedral, MG = trigonal pyramidal, has polar bonds, has dipole moment (b) PCl4-: EPG = trigonal bipyramidal, MG = see-saw, has polar bonds, has dipole moment (c) SnCl3-: EPG = tetrahedral, MG = trigonal pyramidal, has polar bonds, has dipole moment (d) BrCl4-: EPG = octahedral, MG = square planar, has nonpolar bonds, no dipole moment (e) ICl3: EPG = trigonal bipyramidal, MG = T-shaped, has polar bonds, has dipole moment (f) XeF4: EPG = octahedral, MG = square planar, has polar bonds, no dipole moment (g) SF2: EPG = tetrahedral, MG = bent, has polar bonds, has dipole moment

3) Determine the electron-pair geometry (EPG) and molecular geometry (MG) for each of the following molecules. Identify the molecules with a dipole moment: a) SF4 b) CF4 c) Cl2CCBr2 d) CH3Cl e) H2CO

(a) SF4: EPG = trigonal bipyramidal, MG = see-saw, has polar bonds, has dipole moment (b) CF4: EPG = tetrahedral, MG = tetrahedral, has polar bonds, no dipole moment (c) Cl2CCBr2: EPG (either C as central atom) = trigonal planar, MG (either C as central atom) = trigonal planar, has polar bonds, has dipole moment (C-Cl dipoles are stronger than the C-Br dipoles, so they will not cancel) (d) CH3Cl: EPG = tetrahedral, MG = tetrahedral, has polar bonds, has dipole moment (C-Cl bond is more polar than C-H bonds) (e) H2CO: EPG = trigonal planar, MG = trigonal planar, has polar bonds, has dipole moment (C-O bond is more polar than C-H bonds)

Key Concepts and Summary

A dipole moment measures a separation of charge. For one bond, the bond dipole moment is determined by the difference in electronegativity between the two atoms. For a molecule, the overall dipole moment is determined by both the individual bond moments and how these dipoles are arranged in the molecular structure. Polar molecules (those with an appreciable dipole moment) interact with electric fields, whereas nonpolar molecules do not.

1) Explain how a molecule that contains polar bonds can be nonpolar.

As long as the polar bonds are compensated (for example, two identical atoms are found directly across the central atom from one another), the molecule can be nonpolar.

8) Consider the molecules CO32-, CH3OH, CO, and CO2. Which of these is/are polar molecule(s)? (Drawing the Lewis structures for these molecules will help you in answering this question.)

CH3OH and CO

6) There are three possible structures for PCl2F3 with phosphorus as the central atom. Draw them and discuss how measurements of dipole moments could help distinguish among them.

The three possible arrangements are shown below and differ in whether the Cl, F, or one of each is placed in the axial positions of the trigonal bipyramidal geometry. Measuring the dipole moments of these structure, structure (1) would not have any dipole moment since the P-Cl polar bonds would cancel, and the P-F polar bonds would also cancel. Structure (2) would have the largest dipole moment because none of the P-F polar bonds exactly cancel with P-F polar bonds. The P-Cl polar bonds do cancel some of the P-F bond polarity. Structure (3) has an intermediate dipole moment since the two axial F atoms directly cancel and then it is the difference between a single F atom vs 2 Cl atoms in the equatorial positions.

5) The molecule XF3 has a dipole moment. Is X boron or phosphorus?

X must be phosphorus. If X were boron, even though the B-F bonds would be polar, the molecular geometry of BF3 would be trigonal planar, which would not produce a polar molecule. If X is P, PF3 would have a trigonal pyramidal molecular geometry and polar bonds, leading to a dipole moment.

For this question, you will consider the four molecules CH4, NH3, BH3, and H2O. Refer to your Lewis structures and your notes on the molecular polarity for these molecules. What features do the polar molecules in this group all have in common? a) There are no bond dipoles. b) These molecules do not follow the rules of VSEPR. c) Due to some level of asymmetry, the bond dipoles do not appear to cancel each other out. d) Due to symmetry, all of the bond dipoles appear to cancel each other out.

c) Due to some level of asymmetry, the bond dipoles do not appear to cancel each other out.

What features do the nonpolar molecules you observed in the PhET simulation all have in common? a) There are no bond dipoles. b) These molecules do not follow the rules of VSEPR. c) Due to some level of asymmetry, the bond dipoles do not appear to cancel each other out. d) Due to symmetry, all of the bond dipoles appear to cancel each other out.

d) Due to symmetry, all of the bond dipoles appear to cancel each other out.