P in PH3 is sp3 – hybridised. It has three bond pairs and one lone pair around P. Due to stronger lone pairbond pair repulsions than bond pair – bond pair repulsions, the tetrahedral angle decreases from 109°28′, to 93.6°. As a result. PH3 is pyramidal. However, when it reacts with proton, it forms PH+4 ion which has four bond pairs and no lone pair. Now, there are no lone pair-bond pair repulsion. Only four identical bond pair-bond pair interactions exist. PH+4 therefore assumes tetrahedral geometry with a bond angle 109°28° which is higher than in PH3
