Resonance
Resonance occurs when more than one valid Lewis structure can be drawn for a molecule without changing the arrangement of atoms.
Resonance Structures for SO2 (Sulfur dioxide)
And example of resonance structures for a molecule.
Resonance Structures for CO3 2- (Carbonate ion)
Another example of resonance structures.
Resonance Structures for N2O (Nitrous oxide)
A more advanced molecule with resonance.