CHEMISTRY COMMUNITY

Can someone explain the concept of resonance? I still don't really understand what it is exactly and how it relates to drawing Lewis structures.

You can think of resonance as the other possible ways that the electrons are in a compound. They can help you see the most correct drawing of a structure.

When drawing Lewis Structures, it is possible to put bonds between various different atoms, and still yield a 'correct' structure. The concept of resonance accounts for all of these differences. The average of all of the possible resonance structures is what yields the 'true' lewis structure.

I'm not sure if this is correct, but what I understand resonance to be is when you can draw lewis structures of atoms bonding in different, yet equivalent ways. With the example in lecture of NO3-, we can draw it with a double bond connecting an O and the N on the left side, right side, or from the top and it would all be equivalent. This means that the representation of the actual structure of NO3- is a blend of these 3 structures. The "blending" of structures is the resonance.

Hope this helps

Thanks so much: the replies really cleared it up! A follow-up question: if the correct lewis structure is a combination of the possible "correct" ones, why would we still need to calculate formal charge? Is that just to determine the result of resonance?

Formal charge is another factor of forming the structure that you would have to take account of to make sure that the bonds you are forming are actually possible! So even if you have many possible ways of forming the structure, you should take into consideration that the formal charges are correct.

Nienjou Claire 1E wrote:Thanks so much: the replies really cleared it up! A follow-up question: if the correct lewis structure is a combination of the possible "correct" ones, why would we still need to calculate formal charge? Is that just to determine the result of resonance?

Resonance states that some Lewis structures have multiple bonds in different equivalent locations. Formal charge helps you find the correct Lewis structure because ideally the charge should be 0 and should match your structure (if not it will be wrong on the test), if you already know which one is correct then I don't think you should have to calculate it unless the question asks you.