Strength of Hydrogen Bond
Qn: Which of these compounds has the strongest hydrogen bond, HF, H2O or NH3? How do we estimate the strength of hydrogen bond?
Ans: HF. Due to the largest electronegativity difference between H and F. Followed by H2O and then NH3.
Qn: But then why does water have the highest boiling point among them? Doesn’t this mean that water has the strongest hydrogen bond?
Ans: No. This only means water has the most extensive hydrogen bonds as it forms two hydrogen bond per molecule. HF forms only one hydrogen bond per molecule as it only has one hydrogen atom. NH3 forms only one hydrogen bond per molecule as N has only one lone pair per molecule.
So we need to differentiate between the strength of the individual hydrogen bonds and the overall extensiveness of the hydrogen bonds formed 🙂
More on hydrogen bonding here