Bond angle in PH4+ is higher than that in PH3. Why?


Hybridisation of P in PH3 is sp3. Out of the four sp3 hybrid orbitals, three are involved in bonding with the three H-atoms and the fourth one has a lone pair in it.

PH3 when combines with a proton, it forms PH4+ in which the lone pair is absent. So, here all the four hybrid orbitals are involved in bonding.


Now; the lone pair- bond-pair repulsion is stronger than the corresponding bond pair-bond pair repulsion; thus, the tetrahedral shape associated with sp3 bonding in PH3 is changed to pyramidal and due to the absence of lone pair in PH4+, there is no lone pair-bond pair repulsion. Hence; the bond angle in PH4+ is higher than the bond angle in PH3.



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