What Is Resonance

Which of these molecules are polar For each that is polar, specify the direction of its polarity, (a) CH3CI (b) CH2O (c) C2H2 

To determine whether a molecule is polar, first determine if it has polar bonds, and if it does, determine whether the vector sum of the bond dipoles is zero. If the vector sum of the bond dipoles is not zero, the molecule is polar. 

Both chloromethane (CH3CI) and formaldehyde (CH2O) have polar bonds and, because of their geometry, are polar molecules. Because acetylene (C2H2) is linear, and each of its C—H bonds is nonpolar covalent, the molecule is nonpolar. 

Both carbon dioxide (CO2) and sulfur dioxide (SO2) are triatomic molecules. Account for the fact that carbon dioxide is a nonpolar molecule, whereas sulfur dioxide is a polar molecule. 

To describe the carbonate ion, as well as other molecules and ions for which no single Lewis structure is adequate, we turn to the theory of resonance. 

Although carboxylic acids exist in equilibrium with their resonance-stabilized carboxylate anions, it is important to understand that resonance stabilization alone will 

In this chapter, you will learn the tools that you need to draw resonance structures with proficiency. I cannot adequately stress the importance of this skill. Resonance is the one topic that permeates the entire subject matter from start to finish. It finds its way into every chapter, into every reaction, and into your nightmares if you do not master the rules of resonance. You cannot get an A in this class without mastering resonance. So what is resonance And why do we need it  

In Chapter 1, we introduced one of the best ways of drawing molecules, bond-line structures. They are fast to draw and easy to read, but they have one major deficiency they do not describe molecules perfectly. In fact, no drawing method can completely describe a molecule using only a single drawing. Here is the problem. 

Your friend asks you to describe what a nectarine looks like, because he has never seen one. You aren t a very good artist so you say the following  

Picture a peach in your mind, and now picture a plum in your mind. Well, a nectarine has features of both the inside tastes like a peach, but the outside is smooth like a plum. So take your image of a peach together with your image of a plum and meld them together in your mind into one image. That s a nectarine. 

It is important to realize that a nectarine does not switch back and forth ever)- second from being a peach to being a plum. A nectarine is a nectarine all of the time. 

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What is resonance Give three examples of molecules or ions that exhibit resonance, and draw Lewis structures for each of the possible resonance forms. 

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