How to Predict Bond Lengths

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Summer de Vera 2C
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Joined: Fri Sep 28, 2018 12:16 am

How to Predict Bond Lengths

Postby Summer de Vera 2C » Wed Dec 05, 2018 7:55 pm

If you're given the bond length of two bonds in a molecule (e.g. NO2-: N-O=140 pm & N--O=120 pm), how do you predict the NO bond lengths in the molecule? In the example I gave (from the midterm), don't they already tell you what they are?

Julia Go 2L
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Re: How to Predict Bond Lengths

Postby Julia Go 2L » Wed Dec 05, 2018 8:13 pm

You can predict the bond length of each bond because NO2 has resonance. Resonance occurs when you can draw multiple lewis structures of the same molecule just by moving where the double bond occurs. In reality, if a molecule has resonance, the actual bond length will be a combination of all of the lewis structures.

In the case of NO2, you can predict the bond length by taking the average of the two bond lengths. Since there are two lewis structures, the bond length will be a hybrid of them.

120 pm + 140 pm/ 2 = 130pm


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