Strongest Hydrogen Bond: Hydrogen Fluoride (HF)

Hydrogen bonding occurs when a hydrogen atom is bonded to a highly electronegative atom (such as nitrogen, oxygen, or fluorine) and is attracted to another electronegative atom. Among the given options, hydrogen fluoride (HF) exhibits the strongest hydrogen bonding.

Properties of Hydrogen Fluoride (HF):

- Electronegativity: Fluorine is the most electronegative element, and hydrogen has a relatively low electronegativity. This large difference in electronegativity creates a highly polar bond between hydrogen and fluorine, resulting in a strong dipole moment in HF.

- Size of Atom: Fluorine is smaller in size compared to other elements like oxygen or nitrogen. The smaller size allows for closer proximity between the hydrogen and fluorine atoms, enhancing the strength of hydrogen bonding.

- Bond Length: The bond length between hydrogen and fluorine is shorter compared to other hydrogen bonds, such as in water or ammonia. The shorter bond length contributes to a stronger hydrogen bond.

- Bond Strength: The bond energy of HF is higher compared to other hydrogen compounds. This means that more energy is required to break the hydrogen bond in HF, indicating a stronger bond.

Comparison with Other Options:

a) Water (H2O): Water exhibits hydrogen bonding due to the electronegativity difference between oxygen and hydrogen. However, the electronegativity of oxygen is lower than that of fluorine, resulting in weaker hydrogen bonding in water compared to hydrogen fluoride.

b) Ammonia (NH3): Ammonia also exhibits hydrogen bonding due to the electronegativity difference between nitrogen and hydrogen. However, nitrogen is less electronegative than fluorine, resulting in weaker hydrogen bonding in ammonia compared to hydrogen fluoride.

d) Hydrogen Sulfide (H2S): Hydrogen sulfide exhibits weaker hydrogen bonding compared to hydrogen fluoride. Sulfur is less electronegative than fluorine, resulting in a smaller electronegativity difference and weaker hydrogen bonding in hydrogen sulfide.

In conclusion, hydrogen fluoride (HF) exhibits the strongest hydrogen bonding among the given options due to the combination of high electronegativity of fluorine, smaller size of the atom, shorter bond length, and higher bond energy.