Why NH3 is more basic than PH3?

Electronegativity
- Nitrogen in NH3 has a higher electronegativity compared to phosphorus in PH3.
- This leads to a greater ability of nitrogen to attract and hold onto the lone pair of electrons, making NH3 more basic.

Size of the Atom
- Nitrogen in NH3 is smaller in size than phosphorus in PH3.
- The smaller size of nitrogen allows for better overlap of its lone pair of electrons with proton, enhancing its basicity.

Hybridization
- Nitrogen in NH3 is sp3 hybridized, allowing for greater electron density around the nitrogen atom.
- This increased electron density makes it easier for NH3 to donate a lone pair of electrons, making it more basic compared to PH3, which is sp3 hybridized.

Stability of Conjugate Acid
- The conjugate acid formed after accepting a proton from NH3 is NH4+, which is more stable due to resonance.
- On the other hand, the conjugate acid of PH3, PH4+, is less stable and hence, PH3 is less basic.

Conclusion
- In conclusion, the combination of higher electronegativity, smaller size, sp3 hybridization, and stability of the conjugate acid make NH3 more basic than PH3.