Final answer:
The ideal angle between phosphorus-oxygen bonds in a trigonal bipyramidal geometry, which occurs in sp³d hybridized phosphorus molecules, is 120° in the equatorial plane and 90° between the axial and equatorial positions.
Step-by-step explanation:
The ideal angle between the phosphorus-oxygen bonds in molecules where phosphorus exhibits sp3d hybridization, such as in phosphorus pentachloride (PCl5), is based on the geometry of a trigonal bipyramid. Phosphorus uses its 3s orbital, three 3p orbitals, and one 3d orbital to form a set of five sp3d hybrid orbitals. These orbitals are involved in bonding with chlorine atoms, but similar principles can apply to phosphorus-oxygen bonds in analogous molecules.
According to the Valence-Shell Electron-Pair Repulsion (VSEPR) theory, the bond angles between the equatorial positions (three of the hybrid orbitals that lie in the same plane) are 120°, and the bond angle between the axial positions (the two hybrid orbitals on opposite ends of the molecule aligned perpendicularly to the equatorial plane) and equatorial positions is 90°. However, if the molecule were to have a different shape due to repulsion or other effects, like the observed angle in H2O, these angles could slightly differ from the ideal angles predicted by simple hybrid orbital overlap.