Consider the molecules H2O, H2S, H2Se, and H2Te. Which do you expect to have the highest boiling point, and why?

Question

H2O, because it experiences hydrogen bonding.
H2S, because it dissociates and forms ions.
H2Se, because it experiences ion-dipole forces.
H2Te, because it has the most electrons to form a dipole.

Answer 1

The molecule you would expect to have the highest boiling point among H2O, H2S, H2Se, and H2Te is H2O, because it experiences hydrogen bonding.

Hydrogen bonding is a strong type of intermolecular force that occurs when hydrogen is bonded to highly electronegative atoms such as oxygen (in H2O). This strong intermolecular attraction leads to higher boiling points compared to other molecules that may primarily experience weaker van der Waals forces or dipole-dipole interactions.

In contrast:

• H2S, H2Se, and H2Te, while they do have dipole-dipole interactions, do not exhibit hydrogen bonding to the same extent as H2O. Their boiling points are lower due to weaker intermolecular forces.
• The reasoning involving dissociation into ions (as in H2S) or ion-dipole forces (in comparing to H2Se) does not directly apply here because these molecules do not generally dissociate into ions in a way that significantly affects their boiling points under standard conditions.

Therefore, H2O's ability to form hydrogen bonds accounts for its higher boiling point compared to H2S, H2Se, and H2Te.