Why is bond angle in ph3 less than that in nh3?

Answer 1

Both PH3 and NH3 have 3 bonding pairs and 1 lone pair of electrons around the central atom, and so are both trigonal pyramidal in shape. The bond angle in NH3 is less than 109.5º and that in PH3 is less than that in NH3 (maybe around 109º). The reason for this has to due with electronegativity. The N atom is more electronegative than the P atom and thus electron density of N's bonding electrons are closer to the N, and so they exert a greater repulsion on each other. This greater repulsion compared to that seen PH3 makes the bond angle slighter greater in NH3. P being less electronegative than N doesn't draw it's electrons as close so they don't repel as much.