Hydrogen fluoride
In hydrogen fluoride, hydrogen atom is bonded to highly electronegative atom, fluorine (electronegativity = 4). It has been found that in solid state hydrogen fluoride consists of long zig-zag chains of H-F molecules associated by H-bonds. On heating, progressively, the length of the chain shortens, and associated units become quite small.
fig 1.34 - Hydrogen fluoride
Water
In a water molecule, oxygen atom is bonded to two hydrogen atoms. Due to large electronegativity, oxygen atom forms the negative centre whereas each of the hydrogen atom acquires a partial positive charge. Each oxygen atom can form two hydrogen bonds as shown below.
fig 1.35 - Water
Ammonia
In a molecule of ammonia, nitrogen, an electronegative atom is bonded to three hydrogen atoms. The nitrogen atom forms a negative site of the molecule whereas each of three H-atoms acquires a partial positive charge. The ammonia molecules are associated by H-bonds as shown below:
fig 1.36 - Ammonia
