Chemistry I - Lab Chapter 6 - Chemical Bonds
VSEPR Theory
Diatomic molecules like hydrogen (H2), chlorine (Cl2), and molecules like HC1 must
have a linear shape. For more complicated molecules, prediction of the molecular
geometry requires knowing the locations of electrons in bonds.
The VSEPR theory for predicting molecular geometry is based upon the simple
assumption that electrons in molecules repel each other. The letters VSEPR stand for
‘valence-shell electron- pair repulsion,‘ referring to the repulsion between pairs of
bonding valence electrons in the highest energy level. VSEPR theory states that
electrostatic repulsion between the valence electron pairs surrounding an atom causes
these pairs to be oriented as far apart as possible.
To use VSEPR, molecules are classified according to how many electron pairs surround a
central atom. The following chart summarizes the VSEPR theory:
Molecular Shape
Atoms Bonded to Central atom
Unshared e- pairs Molecule Type
1) Linear
2
0
AB2
2) Bent
2
1
AB2E
3) Triangular
3
0
AB3
4) Tetrahedral
4
0
AB4
5) Triangular
3
1
AB3E
6) Bent
2
2
AB2E2
7) Triangular
5
0
AB5
6
0
AB6
Planar
Pyramidal
Bypyramida1
8) Octahedral
A represents the central atom, B represents the atoms bonded to the central atom, and E
represents unshared electron pairs on the central atom.