Question

which intermolecular force is the most important in determining the difference in boiling points of the following molecules?

i₂ (253.8 g/mol)
so₂ (64.1 g/mol)

london dispersion
dipole - dipole (not including hydrogen bonding)
hydrogen bonding

which substance has the stronger total intermolecular forces/the higher boiling point?

1. first, look to see if the substance can hydrogen bond. if so, it likely has the strongest intermolecular forces (e.g., hf > hcl).

1. if you are comparing two molecules of very different molar masses, london dispersion forces are more important (e.g., hbr > hcl).

1. if you are comparing two molecules of very similar molar mass, dipole - dipole forces are more important. the molecule with the greater dipole - dipole forces (the greatest electronegativity difference between the atoms within the molecule) will have the greatest boiling point.

Explanation:

Step1: Analyze intermolecular forces

• \(I_2\) is non - polar, so it has only London dispersion forces.
• \(SO_2\) is polar, so it has dipole - dipole forces (since there is no hydrogen bonding as there is no \(H\) attached to \(N\), \(O\) or \(F\)).
• The molar mass of \(I_2\) (\(253.8\ g/mol\)) is much larger than that of \(SO_2\) (\(64.1\ g/mol\)).
• According to the rule: If you are comparing two molecules of very different molar masses, London dispersion forces are more important.

Step2: Compare boiling points

• Since \(I_2\) has a much larger molar mass, the London dispersion forces in \(I_2\) are stronger than the dipole - dipole forces in \(SO_2\) (because of the large difference in molar mass).
• Stronger intermolecular forces lead to a higher boiling point.

Answer:

• The most important intermolecular force is London dispersion.
• \(I_2\) has the stronger total intermolecular forces and the higher boiling point.