Five-domain geometryTap a bond, ligand, plane, or lone pair100%

Ideal angles: equatorial–equatorial 120°, axial–equatorial 90°, axial–axial 180°.

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3D Trigonal Bipyramidal Geometry Simulation

VSEPR positions, angles, and lone pairs

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Mission: identify three equatorial and two axial positions.

Molecule

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Bond separation100%

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Live measurements

VSEPR notationAX₅

Electron domains5

Molecular shapeTrigonal bipyramidal

Lone pairs0

Steric number = bonded atoms + lone pairs = 5

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Repulsion comparison

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Chapters

3D Trigonal Bipyramidal Geometry Simulation

A trigonal bipyramid is the minimum-repulsion arrangement of five electron domains around a central atom: three equatorial and two axial.

Learning objectives

Distinguish axial and equatorial positions.
Measure ideal 90°, 120°, and 180° angles.
Explain why lone pairs prefer equatorial positions.
Derive seesaw, T-shaped, and linear molecular shapes.
Describe axial–equatorial exchange by Berry pseudorotation.

Equations and rules

Steric number = bonded atoms + lone pairs = 5

AX₅ → trigonal bipyramidal

AX₄E → seesaw; AX₃E₂ → T-shaped; AX₂E₃ → linear

Equatorial site: 2 interactions at 90°; axial site: 3 interactions at 90°

Suggested experiments

Rotate PCl₅ and identify its equatorial triangle.
Compare axial and equatorial bond lengths.
Add lone pairs stepwise from SF₄ to XeF₂.
Run Berry exchange in slow motion and track one ligand.

Questions for exploration

Why is an equatorial position less crowded?
Why can a linear molecule have five electron domains?
Which angles remain ideal after a lone pair is added?

Common misconceptions

Five domains are not arranged as a flat pentagon.
Axial and equatorial sites are not identical.
Molecular shape names omit lone-pair positions.
XeF₂ is linear, but its electron-domain geometry is trigonal bipyramidal.

Applications

VSEPR prediction, phosphorus halides, hypervalent molecules, ligand exchange, spectroscopy, and reaction mechanisms.

Quiz

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