Which one of the following is expected to exhibit resonance? (A) #CO_2# (B) #NH_4^(+)# (C) #HCN# (D) #NO_2""^(-)#

1 Answer
Jun 28, 2015

Answer:

The expected answer is probably D) #"NO"_2^-#.

Explanation:

Both #"CO"_2# and #"HCN"# also exhibit resonance, but they have only one major contributor. #"CO"_2# has two major contributors.

To determine if resonance is possible, you draw the Lewis structure and then see if you can put the electrons in different locations.

A) #"CO"_2#

The Lewis structure for #"CO"_2# is

figures.boundless.com

There are two other resonance contributors, but they involve charge separation, so they are minor contributors.

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B) #"NH"_4^+#

The Lewis structure of #"NH"_4^+#is

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This is the only Lewis structure — no resonance.

C) #"HCN"#

The Lewis structure of #"HCN"# is

wps.prenhall.com

You can draw a structure with a #"C=N"# bond, but it puts formal charges on #"C"# and #"N"#, so it is a minor contributor.

www.chem.purdue.edu

D) #"NO"_2^-#

#"NO"_2^-# has two equivalent Lewis structures. They are both major resonance contributors.

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