The specific three dimensional arrangements of atoms in molecules are referred to as molecular geometry. We also define molecular geometry as the positions of the atomic nuclei in a molecule. There are various instrumental techniques such as X-Ray crystallography and other experimental techniques which can be used to tell us where the atoms are located in a molecule. Using advanced techniques, very complicated structures for proteins, enzymes, DNA, and RNA have been determined. Molecular geometry is associated with the chemistry of vision, smell and odors, taste, drug reactions and enzyme controlled reactions to name a few. Molecular geometry is associated with the specific orientation of bonding atoms. A careful analysis of electron distributions in orbitals will usually result in correct molecular geometry determinations. In addition, the simple writing of Lewis diagrams can also provide important clues for the determination of molecular geometry. Click on a picture to link to a page with the GIF file and a short discussion of the molecule.
Steric Number (# bonded atoms + # electron pairs)
6
5
4
3
2
AX6 octahedral
AX5
trigonal bipyramidal
AX4
tetrahedral
AX3
trigonal planar
AX2
linear
1 lone pair of electrons
AX5E
square pyramidal
AX4E
distorted tetrahedron
AX3E
pyramidal
AX2E
nonlinear
AXE
linear
2 lone pairs of electrons
AX4E2
square planar
AX3E2
T-shaped
AX2E2
bent
AXE2
linear 3 lone pairs of electrons
AX3E3
T-shaped
AX2E3
linear
AXE3
linear
4 lone pairs
AX2E4
linear
AXE4
linear
5 lone pairs
AXE5
linear
Valence Shell Electron Pair Repulsion (VSEPR) theory
Electron pairs around a central atom arrange themselves so that they can be as far