Ionic compounds tend to have higher boiling points than covalent substances do. Both ammonia, NH3, and methane, CH4, are covalent compounds yet the boiling point of ammonia is 130⁰C higher than that of methane. What might account for this large difference?

Polarity of the covalent bond and nature if intermolecular interaction.

Explanation:

The type and degree of intermolecular interaction within covalent molecules significantly affect their boiling points. Secondly, the electro negativity difference between the atoms also has a lot to do with the polarity of the covalent bond, and influences the nature of intermolecular interaction found in the molecule and ultimately influences its boiling point.

Ammonia is a polar molecule due to the significant magnitude of electronegativity difference between hydrogen and nitrogen. This accounts for the fact that the molecule possess hydrogen bonding in solution. The hydrogen bond is a strong intermolecular interaction which increases the boiling points of covalent compounds in which it is found.

On the other hand, methane is a nonpolar covalent molecule whose dominant intermolecular forces are weak Vanderwaals forces. Hence it shows a lower boiling point.

Hence polarity and nature of intermolecular interaction accounts for the large difference in boiling points between methane and ammonia.

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