The molecular geometry of PH3 (phosphine) is trigonal pyramidal. This shape arises because phosphorus has five valence electrons, three of which are used to form bonds with hydrogen atoms, and the remaining two form a lone pair. The lone pair exerts a repulsive force on the bonding pairs, pushing them slightly closer together and resulting in a pyramidal shape.
In a trigonal pyramidal geometry, the central phosphorus atom is at the apex, and the three hydrogen atoms form the base of the pyramid. The bond angles in PH3 are approximately 93.5 degrees, which is less than the ideal 109.5 degrees of a perfect tetrahedron due to the lone pair’s repulsion.
This molecular geometry is crucial in understanding the chemical behavior and reactivity of phosphine, especially in its interactions with other molecules and its role in various chemical reactions.