Exhibits, Shows and Displays

How can you tell if a substance exhibits resonance?

Basically I have a list of several substances, like CH_4 and NO_2 (-1 charge on the NO_2). Can someone explain to me what resonance is, and how I can figure out if these things exhibit it? Note: Underscore means a subscript (my computer won't do it right)

Public Comments

1. “Resonance in chemistry is a tool used to represent and model certain types of non-classical molecular structures. Resonance is a key component of valence bond theory and arises when no single conventional model using only even number of electrons shared exclusively by two atoms can actually represent the observed molecule” –Wikipedia Basically, in the construction of Lewis Dot Diagrams, there are possiblitlities where ther can be more than one way to draw the atom. What I mean is, is that in a molecule where there are multiple types of bonding, for example, NO2- has a single bond and a double bond. When drawing the structure, you can either put the single bond on the left of the N in the middle, or to the right of the Nirtogen in the middle. I don’t know if you really understand, its difficult to explain with just a keyboard.