VSEPR Theory

Molecular Geometry - VSEPR Theory and Bond Angles

http://science.jrank.org/pages/4405/Molecular-Geometry-VSEPR-theory-bond-angles.html

This article has to do with how we can predict what angles atomic covalent bonds will form at. This is needed to tell what shapes molecules will form. For example, one hears of six-carbon and five-carbon rings in sugars such as glucose, but never of 4 or 3 carbon rings. Or, why do the oxygens and carbon in CO2 form in a line, but the oxygen and hydrogens in H2O form a 108 degree angle? All of those molecules are important to life, so it is essential that we understand why they form the way they do.

VSEPR theory explains those questions in terms of electrons. They like to repel each other, each being negatively charged, and so they become as far away form each other as they can be. In water, the two nonbonding pains in oxygen are filling up space and driving the hydrogens away from 180 degrees.

However, to understand VSEPR theory, we have to give up Bohr's model with the electrons as particles in nice orbits, and take the quantum physics model with electrons as both particles and waves inhabiting probability clouds.

If you don't understand something in this post, go look at Wikipedia:
http://en.wikipedia.org/wiki/VSEPR_theory
http://en.wikipedia.org/wiki/Atomic_orbital
And if you don't understand how an electron is both a wave and a particle, stop trying. It's a fundamental property of the universe
http://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality