Question

Which among the following compounds show strongest hydrogen bonding?
A. \[{H_2}O\]
B. \[N{H_3}\]
C. HF
D. \[{H_2}S\]

Answer 1

Hint: A hydrogen bond is formed when the positive end of one molecule is attracted to the negative end of another. It occurs only when there is a very large difference between the electronegativity of the H atom and the other atom participating to form the molecule.

Complete step by step solution:
As it is already mentioned, only atoms having a large difference in electronegativity compared to hydrogen atom can have a hydrogen bond. Hence only atoms like N, O and F having an electronegativity value of 3.0, 3.5 and 4.1 respectively, can participate in a hydrogen bonding.
Looking into the options, \[{H_2}S\] cannot be our answer as the electronegativity value of sulphur is not much different as compared with hydrogen.
Now, we have HF, \[N{H_3}\] and \[{H_2}O\] all of these compounds are held together by hydrogen bonding.
As we know, across the periodic table, as we move on from left to right, electron number is increased on the outermost shell and thus electronegativity is also increased. This increased electronegativity in turn ensures a more stronger hydrogen bonding between the atoms. Accordingly, Flourine (F) has the highest electronegativity, preceded by Oxygen(O) and then Nitrogen(N).
Thus, HF has the strongest hydrogen bonding.
Hence, the correct answer is option (C).

Note: Hydrogen bonding results in a dipole-dipole interaction among the participating atoms. Hydrogen bonding is somewhat stronger than Van der Walls interaction and weaker than covalent or ionic bonds.