Four electron domains around a central atom is known generally as tetrahedral and has three major variations you should know:
AX4 - tetrahedral
AX3E - trigonal pyramidal
AX2E2 - angular
AX4 - Tetrahedral
| Molecule | Lewis Structure | 3-D Structure | Comments |
| CH4 |  |
 |
The H-C-H angle is the classic tetrahedral angle of
109.5° A very interesting result of molecular orbital theory is that CH4 has one bond different than the other three. |
| CCl4 |  |
 |
tetrahedral |
| NH4+ |  |
 |
tetrahedral |
AX3E - Trigonal pyramidal
| Molecule | Lewis Structure | 3-D Structure | Comments |
| NH3 |  |
 |
Since the nonbonding pair is larger (and more repulsive) than a bonding pair, the hydrogens are pushed together and the H-N-H bond angle is 107.2° The bond angle in NF3 is 102.3° due to the greater electronegativity of F. |
| H3O+ |  |
 |
The H-O-H bond angle varies depending on the presence of other ions in the solid. |
AX2E2 - Angular
| Molecule | Lewis Structure | 3-D Structure | Comments |
| H2O |  |
 |
The H-O-H bond angle is 104.5° |
Copyright © Dr. Donald L. Robertson (Modified: 09/13/2009)