Trigonal bipyramidal | Geometry of PF5?

In this blog we will discuss about the geometry of phosphorus pentafluoride, it’s structure and some of it’s properties. We will also discuss whether it is a Lewis acid or not. This blog will provide you an overview about the geometry of trigonal bipyramidal structure. We will try to find the answers of our questions related to trigonal bipyramidal. After observation, we will be able to determine the geometry of PF5 and we will be able to know some interesting factors about phosphorus pentafluoride.

What is trigonal bipyramidal geometry?

A trigonal bipyramidal shape establishes when a central atom is surrounded by five atoms in a molecule. In this geometry, atoms are arranged in two planes. Three atoms are in the same plane with bond angles of 120 degrees while the other two atoms are on opposite ends of the molecule. In this geometry bond angles surrounding the central atom are not identical because there is no geometrical arrangement with five terminal atoms in equivalent positions.

trigonal bipyramidal

Some interesting facts about trigonal bipyramidal geometry

Coordination number in trigonal bipyramidal structure is 5, point group is D3h, polarity is 0 and bond angles are 120 degrees and 90 degrees. They have zero lone pairs with steric number 5. They are non polar in nature. Their hybridization is sp3d.

What is the geometry of phosphorus pentafluoride PF5?

PF5 is a phosphorus halide. It is a toxic and colorless gas which fumes in the air.

The axial and equatorial fluorine atoms rapidly exchange positions because of low barrier for pseudo-rotation via the berry mechanism. R. Gutowsky noticed the apparent equivalency of the F centers in PF5 and Stephen Berry described the explanation (who also discovered berry mechanism).

Trigonal bipyramidal geometry of PF5

Single crystal X-ray studies show that the PF5 has trigonal bipyramidal geometry. Phosphorus pentafluoride has 5 regions of electron density around the central phosphorus atom 5 bonds pair and no lone pair. The resulting shape is a trigonal bipyramidal in which three fluorine atoms occupy equatorial and two occupy axial positions. The F-P-F angle between equatorial positions is 120 degrees, between the axial and equatorial positions it is 90 degrees.

Is PF5 a Lewis acid?

Yes, PF5 is a Lewis acid. This property is relevant to its ready hydrolysis. A well studied adduct is PF5 with pyridine. With primary and secondary amines, the adducts convert readily to dimeric amido-bridged derivatives with the formula [PF5 (NR2)]2.

How PF5 was prepared initially?

It was first prepared in 1876 by the fluorination of phosphorus pentachloride using arsenic trifluoride.

                         3 PCl5 + 5 AsF3 → 3PF5 + AsCl3

Write some properties of PF5

  • It has molar mass of 125.966g/mol.
  • It’s density is 5.527 kg/m3.
  • Melting point of PF5 is -93.78C and boiling point is -84.6C.
  • It is a colorless gas with unpleasant odor.
  • It is non flammable gas.
  • PF5 is very toxic gas and can cause pulmonary edema.


In trigonal bipyramidal geometry, the central atom is surrounded by five atoms. Trigonal bipyramidal geometry consist of two planes, one is axial and the other is equatorial. Three atoms are on equatorial position and two are on axial position. PF5 is the best example of this geometry. In PF5, The F-P-F angle between equatorial positions is 120 degrees, between the axial and equatorial positions it is 90 degrees. It is a Lewis acid.

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