Let's compare the three dimensional or mathematical shape (where we have put the sides on the figures or placed planes to show the flat or planar nature of the structure) with the molecular geometry that chemists refer to.  The names tend to be derived from the shape of the solid figure and the number of sides, while chemists are interested in the arrangement of the atoms at the corners (or vertices) around a central atoms, which is buried at the center of the structure.

Mouse over the images to start or repeat the movie of each.


trigonal                            tetrahedral                      pyramidal

BF3                                    CH4                                NH3

trigonal bipyramidal



octahedral                        square planar

SF6                                    XeF4

How about the hybridization of carbon and its geometry?


sp3                                sp2                                sp

ethane                             ethene                             ethyne

View the Chime structure of the iron EDTA complex ion given below.  If you move the cursor over an atom and click, it will identify the atom on the lower left hand corner of the browser screen.  

What is the geometry of the iron atom and what atoms are the surrounding it?  What is the geometry of the nitrogen atoms?  How many trigonal carbon atoms are in the structure?  How many tetrahedral carbons?

View the structure of chlorophyll a and identify the geometry of the magnesium atom.  What is the magnesium bonded to?  What is the geometry of the nitrogen atoms?

Structures produced in Spartan '04 and movies captured using CamStudio (freeware).

Scott A. Sinex        Prince George's Community College        January 2004