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Question
Why does NH3 form hydrogen bond but PH3 does not?
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Solution 1
Nitrogen is highly electronegative as compared to phosphorus. This causes a greater attraction of electrons towards nitrogen in NH3 than towards phosphorus in PH3. Hence, the extent of hydrogen bonding in PH3 is very less as compared to NH3.
Solution 2
Nitrogen has an electronegativity value of 3.0, which is much higher than that of H (2.1). As a result, N-H bond is quite polar and hence NH3 undergoes intermolecular H-bonding.
Phosphorus has an electronegativity value of 2.1. Thus, the P–H bond is not polar, and hence PH3 does not undergo H-bonding.
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