Trigonal Bipyramidal Geometry
A shape with five bonded atoms occupying three equatorial and two axial positions around a central atom.
Formula / equation
AX₅
Unit
degrees
In depth
The five positions are not equivalent: equatorial bonds sit at 120° to one another while axial bonds lie at 90° to all three equatorial ones. Lone pairs and bulky groups therefore prefer the less crowded equatorial sites, and the positions can interchange by Berry pseudorotation.
Examples in the real world
PCl₅ in the gas phase, and PF₅, whose fluorines exchange so fast that NMR sees only one environment.