Chemistry

Molecular Geometry
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