| MadSci Network: Chemistry |
Ok, it is very simple:
The double covalent bond: This is the more stable configuration. Nearly all the oxygen found, in normal environmental conditions (25 C, 1 atm) in is this state ( 1 sigma orbital, and 1 Pi orbital).
But, if you take the oxygen, and you put it in some very unhabitual condition ( like 5000 atm, and 1000C), it is possible that the molecular oxygen have a different configuration. Maybe the electron in the double bond jump in a more excited state. In this case, that will be the resonance state of the oxygen that will appear:
(+)O--O(-)
But there is also another fact: The Oxygen is a very electronegative atom (this atom attracts the electron). So, it will make the covalent bond weaker, because the covalent bond is based on the share of two electrons between two atoms. So, if the oxygen attract the electron, the sharing of electrons will be less strong. If we construct, arbitrarily, a scale of strength of a covalent bond, and we say that (1) is the normal, typical covalent bond. Normally, for the Oxygen molecule, that would be 2 ( 2 covalent bond), but because the bond is weak, and because the second covalent bond ( that we are calling Pi bond) is weaker than the sigma bond ( the first covalent bond), so we can say that, on this scale, the number that would represent the oxygen molecule bonding character would be 1.5. It is like if the configuration of oxygen would be always switching between the two bonds configuration, and the configuration with one bond. This is what we are calling resonance.
Daniel @webadmin@ Picard