PH3:
Trigonal pyramidal: Phosphorus atom has five electron in its outermost orbit. H-atoms contribute one electron each to make in all 8 electrons around P-atom. Thus, 4 pairs of electrons would be distributed in a tetrahedral fashion around the central atom. Three pairs form three P-H bonds while the fourth pair remains unused. Due to repulsion between the bonding and lone pairs if electrons, the angle HPH is not exactly tetrahedral (109° 28'). The actual HPH angle is 93.3°. Thus PH3 is a trigonal pyramidal molecule.
