Chemistry I / Lewis Structures, Formal Charge and Resonance
Practice question · Fill in the blanks

Complete the account of what the ozone bond lengths tell us.

Both bonds in ozone measure 128 pm, which lies ______ a single bond (148 pm) and a double bond (121 pm). Because the two bonds are ______, no drawing with one of each can be literally true: the real molecule is a single ______ rather than a structure that ______ between two forms.

Word bank: between · identical · resonance hybrid · alternates · shorter than

Hints
  1. Start by comparing 128 pm with the two reference lengths.
  2. If the molecule flickered between forms, the two bonds would still have to differ at any instant.
Show the answer

Both bonds in ozone measure 128 pm, which lies between a single bond (148 pm) and a double bond (121 pm). Because the two bonds are identical, no drawing with one of each can be literally true: the real molecule is a single resonance hybrid rather than a structure that alternates between two forms.

Why

The measured length sits between the single and double values, and crucially the two bonds are identical. A molecule alternating between drawings would still have one long and one short bond at every instant, so the truth is one averaged hybrid that whole-number bond notation simply cannot express.

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