In terms of bonding, state the order of boiling point of propane, ethanol and ethanal and why.

The molecule with the highest boiling point is ethanol. This is because of the hydrogen bonding that occurs between molecules from the electronegative oxygen atom and electropositive hydrogen atom. The second highest boiling point is that of ethanal. This is due to the large difference in electronegativity between the oxygen and carbon atoms. This causes dipole-dipole forces between molecules which are weaker than hydrogen bonds. This means that much less energy is required to break these bonds. In propane, only London dispersion forces exist because there is no permanent polarity within the molecule. This means it has a lower boiling point compared to ethanol and ethanal so requires little energy to break these bonds and separate the molecules.