# What intermolecular interactions occur for "(i) dihydrogen", "(ii) acetone", "(iii) propane", and "(iv) ammonia", "(v) water", and "(vi) hydrogen fluoride"?

## Can you rank these in order of volatility?

Jul 22, 2017

But van der Waals interactions are weak, and thus dihydrogen, for which ONLY dipersion forces operate, is the MOST VOLATILE of the given substances, with a normal boiling point of $- 253.9$ ""^@C. Propane, which also possesses minimal intermolecular interaction, is next cab off the volatility rank.
For acetone, there is some degree of dipole-dipole interaction, in that there is some polarity in the carbonyl bond, i.e. $\stackrel{\delta +}{C} = \stackrel{\delta -}{O}$; compare the boiling point of acetone, $56$ ""^@C, with that of propane, $- 42$ ""^@C, the which only has dispersion forces operating.
For ammonia, hydrogen chloride, and water a special type of dipole-dipole interaction operates, $\text{hydrogen bonding}$, and this occurs where hydrogen binds to a strongly electronegative element such as oxygen, or fluorine, or nitrogen. You should look up the normal boiling points of $H F$ and $N {H}_{3}$, and ${H}_{2} O$, and compare them to their lower group hydrides.