Trigonal Bipyramidal Electron Geometries (AX5, AX4E,
AX3E2 and AX2E3)
Molecules in this category may have three, four, five or six
atoms. The configuration is specified as AX5 for the
case with six total
atoms, AX4E for the case with five atoms, AX3E2
for the case with four and AX2E3 for the
case with three. Remember the "E" represents electron groups that are
not involved in bonding, the "X" atoms around the central atom
and the "A" is the central atom. Molecules of the type AX5 are
described as having a trigonal
bipyramidal molecular geometry,
those of type AX4E a seesaw molecular geometry,
those of type AX3E2 a T-shaped
molecular geometry, and those of type AX2E3 as linear.
-
Example AX5 Molecules (trigonal bipyramidal)
-
Example AX4E Molecules (seesaw)
Note how loan pairs repel bonds decreasing the bond angle to < 90°, < 120° and < 180°.
-
Example AX3E2 Molecules (T-shaped)
Note how loan pairs repel bonds decreasing the bond angle to < 90°, < 120° and < 180°.
-
Example AX2E3 Molecules (linear)
Note how loan pairs occupy the equatorial locations (separated by 120°).
-
Molecular Viewer Help
When you select a molecule you will see a rotating image of the molecule displayed using the JSmol applet.Rotate the molecule Hold down the mouse button and drag the cursor over the image. Zoom the view Hold down the shift key and the mouse button while dragging up or down over the image. On a touchpad two finger drag-up zooms in. Many more options in the right-click menu The right-click menu can also be activated by clicking on the JSmol icon at the lower right of the viewer.
Additional instructions for the viewer.
If your browser is not Javascript capable you can still download the molecule files readable by Jmol and then use Jmol to view the files. See the tutorial introduction for more information.
Reference and Technical Info
* Measured geometry (from spectroscopic measurements) sourced from:
The NIST Computational Chemistry Comparison and Benchmark Database
NIST Standard Reference Database Number 101
Release 22, May 2022, Editor: Russell D. Johnson III
https://cccbdb.nist.gov/
Other geometries are based on estimates from quantum computations.
.gif)
Last Update: July 20, 2026
Expires: --
J. Gutow
Expires: --
J. Gutow