# Why do PBr3 and PCl3 have larger bond angles than PH3?

According to the Colby Chemistry Database, the bond angle of $$\ce{PBr3}$$ and $$\ce{PCl3}$$ are around $$101$$ degrees, but the bond angle of $$\ce{PH3}$$ is $$92$$ degrees. (Source: PCl3 PBr3 PH3)

There was a previous question on Stack Exchange about the bond angle difference in $$\ce{PF3}$$ and $$\ce{PH3}$$ here: PF3 and PH3, but the accepted answer mentions back bonding as a factor to increase the bond angle in $$\ce{PF3}$$. I was skeptical about this answer, because in $$\ce{PCl3}$$ and $$\ce{PBr3}$$, there should be less back bonding than in $$\ce{PF3}$$ because bromine and chlorine are both much larger than fluorine and there will be worse orbital overlap between the halogen. Less back bonding should make the bond angle of $$\ce{PCl3}$$ and $$\ce{PBr3}$$ smaller than that of $$\ce{PF3}$$, if back bonding were the major factor here? In reality, that is not the case. Why not?

The larger angles can simply be explained as a result of repulsion between the larger atoms of $$\ce{Br}$$ and $$\ce{Cl}$$. Hydrogen atoms in $$\ce{PH3},$$ as the are so small, experience less repulsion as compared to $$\ce{Br}$$ atoms in $$\ce{PBr3}$$ or $$\ce{Cl}$$ atoms in $$\ce{PCl3},$$ therefore the larger bond angles in $$\ce{PBr3}$$ and $$\ce{PCl3}.$$