Why is melting point of ammonia lower than water?
The melting point of a substance is based upon the polarity of the bonds that make up the substance. In water, the O-H bond has a difference in electronegativity of 1.4 (Pauling’s Scale) and in ammonia, the N-H bond has a difference in electronegativity of .9. Therefore, it takes more energy to break apart the O-H bond because the polarity is so great, and this is why it has a higher melting point than ammonia.
