CP Sci 9- 1st Sem.
Gen Chem - 1st Sem.
The Shapes of Small Molecules:
1. Define VESPR theory and explain its relationship to the shape of molecules.
2. Name and describe 5 basic shapes of molecules.
3. Define the term hybrid orbital and explain how it differs from atomic orbital.
4. Explain two important trends in bond length.
ball-&-stick model valence-shell electron pair repulsion theory bond angle hybrid orbital
As we learned in the previous chapter the structural formula of a molecule can give a clear picture of the arrangement of atoms in a molecule. Its limitation is that it gives only a one dimensional picture of the molecule. This is why many chemists prefer ball-and-stick models. Ball-and-stick models let us see the molecules in three dimensions which aids in our understanding of the characteristics of the molecules. There are 5 basic shapes that can be easily displayed by this model system.
Consider the following examples:
Ammonia (NH3) - pyramidal
Carbon dioxide (CO2) - linear
Boron triflouride (BF3) - trigonal planar
Methane (CH4) - tetrahedral
Water (H2O) - bent
Bonding of atoms can be further explained by the concept of hybrid orbitals. A hybrid orbital describes the interaction of the valence electrons an atom as they approach another atom. Consider the following chart:
You will notice as electrons become available the orbitals assume the shape that best fits with the VESPR model. Here are some examples for you.
Trends in bond length give us an idea of the reactivity of certain compounds. Here are some simple rules to follow when determining bond length.
Last modified: September 05, 2004