Trigonal bipyramidal molecular geometry

A molecular geometry with three atoms arranged in an equatorial plane around a central atom and two atoms above and below that plane on an axial line.

VSEPR theory: A model that predicts molecular shapes by treating regions of valence-electron density as mutually repelling. It predicts the five-direction arrangement around the central atom.
Phosphorus pentachloride: A molecular compound, PCl₅, with five chlorine atoms bonded to one phosphorus atom. Its gas-phase molecules provide the standard example of this geometry.
Electron-domain geometry: The arrangement of bonding and nonbonding electron domains around a central atom. Its five-domain arrangement can underlie several distinct molecular shapes.
Seesaw molecular geometry: A molecular shape with four bonded atoms and one lone pair around a central atom in a trigonal-bipyramidal electron arrangement. It results when one equatorial atom position is occupied by a lone pair.
Axial position: A position along the axis passing through a molecular center, perpendicular to an equatorial plane. The two axial sites experience stronger repulsions than the equatorial sites.
Phosphorus pentafluoride: A molecular compound, PF₅, with five fluorine atoms bonded to one phosphorus atom. Its five equivalent bonds occupy three equatorial and two axial sites.
Lone pair: A pair of valence electrons localized on one atom and not shared in a bond. Lone pairs occupy positions in the electron arrangement but are omitted from the molecular shape.
T-shaped molecular geometry: A molecular shape with three bonded atoms arranged like the letter T around a central atom. It results when two equatorial positions are occupied by lone pairs.
Equatorial position: A position in the plane perpendicular to a molecule's principal axis. Three equatorial sites form the plane at the heart of this geometry.
Sulfur tetrafluoride: A molecule, SF₄, with four fluorine atoms and one lone pair around sulfur. The lone pair occupies an equatorial site, producing a seesaw molecular shape.

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