Lewis Structures and the “Real” 3D
Lewis Structures and the “Real” 3D-Shape of Molecules
Shapes and Polarities of Molecules
A. Molecular Shape or Geometry - The way in which atoms of a molecule are arranged in
space. It refers to the actual position of the nuclei.
B. What influences molecular shape ? The major factor is the tendency of valence
electrons whether they are involved in bonding or not to repel each other.
C. The theory which describes molecular shape is called
VALENCE SHELL ELECTRON PAIR REPULSION
Because of their negative charge valence electrons will arrange themselves about a
central atom in a way that minimizes repulsion between electrons.
D. Why is molecular shape important?
1. Molecular shape influences molecular polarity (the degree of separation of plus
and minus charges in a molecule)
2. Molecular polarity influences such physical properties as melting point,
boiling point, and solubility.
Common molecular shapes include:
2. Bent (angular)
Hydrogen Chloride, HCl, a Linear Molecule
Water, H2O, a Bent or Angular Molecule
Ammonia, NH3, a Pyramidal Molecule
Methane, CH4, a Tetrahedral Molecule
VSEPR Arrangements of Groups Around an Atom
Electron Groups are Single Bonds, Multiple
Bonds, or Unshared Pairs of Electrons
H O H
O O O
VSPER Molecular Shape Table
Formaldehyde, CH2O, a Planar, Triangular Molecule
Borane, BH3, a Planar, Triangular Molecule
Carbon Dioxide, CO2, a Linear Molecule
O C O
Acetylene and Hydrogen Cyanide, Linear Molecules
Covalent Bonds Exist in a Continuum
When describing the polarity of a molecule, we must
consider bond polarities as
quantities with magnitude and direction.
Some molecules are inherently polar because of the atoms which
they contain and the arrangement of these atoms in space.
A crude representation
of a polar molecule
Other molecules are considered nonpolar