Question 9 of 32intermediate💡 UnderstandShort Answer2 marks

Explain the important aspects of resonance with reference to the CO₃²⁻ ion.

Correct Answer

A single Lewis structure of CO32−CO_3^{2-} showing two single and one double bond is inadequate as it represents unequal bonds. Experimentally, all carbon to oxygen bonds in CO32−CO_3^{2-} are equivalent. Thus, it is best described as a resonance hybrid of three canonical forms (I, II, and III).

The important aspects of resonance here are:

  1. The canonical forms have no real existence; the molecule does not exist for a fraction of time in one form and for other fractions in other forms, nor is there an equilibrium between them.
  2. The actual ion has a single structure, the resonance hybrid, which cannot be depicted by a single Lewis structure.
  3. Resonance stabilizes the molecule because the energy of the resonance hybrid is less than the energy of any single canonical structure.
  4. It averages the bond characteristics as a whole, making all C-O bonds equivalent.
Exercise: EXERCISES | Q: 4.11 | (Page 34)
For More Understanding

Explanation

The answer explains that a single Lewis structure cannot accurately represent the experimentally observed equivalent C-O bonds in the carbonate ion. It then lists the key aspects of resonance as provided in the text: the non-existence of canonical forms, the single nature of the resonance hybrid, the stabilization due to lower energy, and the averaging of bond characteristics.

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