Questions: Which of the following molecules will have dipole-dipole forces as the strongest intermolecular force? Choose three. CO BF3 NCl3 CO2 HF CH2F2

Solution Steps

Dipole-dipole forces occur in molecules that have a permanent dipole moment, which means the molecule must be polar. To determine if a molecule is polar, we need to consider its molecular geometry and the electronegativity of its atoms.

1. CO (Carbon Monoxide): CO is a polar molecule because of the difference in electronegativity between carbon and oxygen, and it has a linear structure.
2. $\mathrm{BF}_{3}$ (Boron Trifluoride): $\mathrm{BF}_{3}$ is nonpolar because it has a trigonal planar structure, and the dipoles cancel out.
3. $\mathrm{NCl}_{3}$ (Nitrogen Trichloride): $\mathrm{NCl}_{3}$ is polar due to the lone pair on nitrogen, which creates a net dipole moment.
4. $\mathrm{CO}_{2}$ (Carbon Dioxide): $\mathrm{CO}_{2}$ is nonpolar because it has a linear structure, and the dipoles cancel out.
5. HF (Hydrogen Fluoride): HF is polar due to the significant difference in electronegativity between hydrogen and fluorine.
6. $\mathrm{CH}_{2} \mathrm{~F}_{2}$ (Difluoromethane): $\mathrm{CH}_{2} \mathrm{~F}_{2}$ is polar because the dipoles do not cancel out in its tetrahedral structure.

Based on the analysis, the molecules with dipole-dipole forces as the strongest intermolecular force are:

• CO
• $\mathrm{NCl}_{3}$
• HF
• $\mathrm{CH}_{2} \mathrm{~F}_{2}$

We need to choose three out of these four. The three molecules with the strongest dipole-dipole forces are:

• CO
• $\mathrm{NCl}_{3}$
• HF

Final Answer