Lewis theory: allows us to determine the structural formula from the chemical formula

e.g. C₂H₆O  →  CH₃CH₂OH

For an animated tutorial on creating Lewis structures, go to:

http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interface.asp?chapter=chapter_08&folder=lewis_structures

Valence shell electron pair repulsion theory (VSEPR): allows us to determine three-dimensional molecular shape from electron pair geometry.

chemical formula   →   structural formula   →   [3 dimensional] molecular shape

Example of using molecular models:

http://www.sciencedaily.com/releases/2009/04/090421080506.htm