Resonance in chemistry is a tool used (predominately in organic chemistry) to represent certain types of molecular structures. Resonance is a key component of valence bond theory and arises when no single conventional model using only single, double or triple bonds can account for all the observed properties of the molecule. Lewis dot diagrams often cannot represent the true electronic structure of a molecule. While one can only show single, double or triple covalent bonds using these diagrams, one finds that the observed molecule does not match either of these structures but rather has properties in some sense intermediate to these. Resonance structures are then employed to approximate the true electronic structure.