Question

Account for the following:

PH₃ is a weaker base than NH₃.

Answer 1

1. PH₃ is a weaker base than NH₃ because phosphorus is larger than nitrogen, so its lone pair is more spread out and less concentrated.
2. In NH₃, the smaller nitrogen atom holds the lone pair closer, increasing electron density and making it easier to donate.
3. The low electronegativity difference between P and H in PH₃ makes the P-H bond less polar, reducing the availability of the lone pair.
4. Due to this, PH₃ has a lower tendency to donate its lone pair to acids, making it a weaker base than NH₃.

These points explain the weaker basic nature of PH₃ compared to NH₃.