Question

which intermolecular force is the most important in determining the difference in boiling points of the following molecules?
ch₃oh (32.0 g/mol)
ch₃sh (48.1 g/mol)
london dispersion
dipole - dipole (not including hydrogen bonding)
hydrogen bonding, because one of the molecules can hydrogen bond
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).
2. if you are comparing two molecules of very different molar masses, london dispersion forces are more important (e.g., hbr > hcl).
3. 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 hydrogen - bonding possibility

Hydrogen bonding occurs when \(H\) is bonded to \(N\), \(O\), or \(F\). In \(CH_{3}OH\), \(H\) is bonded to \(O\), so \(CH_{3}OH\) can form hydrogen bonds. In \(CH_{3}SH\), \(H\) is bonded to \(S\) (not \(N\), \(O\), or \(F\)), so \(CH_{3}SH\) cannot form hydrogen bonds.

Step2: Compare intermolecular forces

Since \(CH_{3}OH\) can hydrogen - bond (a stronger intermolecular force than dipole - dipole and London dispersion for these molecules) and \(CH_{3}SH\) cannot.

Answer:

Hydrogen bonding, because one of the molecules can hydrogen bond.