11th Class Chemistry Chemical Bonding and Molecular Structure

  • question_answer 88)   Explain why \[CO_{3}^{2-}\] ion cannot be represented by a single Lewis structure? How can it be best represented?


      Carbonate ion can be represented by the following Lewis structure.   The calculated values of bond distances between carbon and oxygen in C = 0 and C-0 are 1.22\[\overset{{}^\circ }{\mathop{\text{A}}}\,\] and 1.43\[\overset{{}^\circ }{\mathop{\text{A}}}\,\]respectively but the observed bond length is neither 1.22 nor 1.43\[\overset{{}^\circ }{\mathop{\text{A}}}\,\] but some what between these two values. The other observation is that all the three bond lengths are equal. Hence, the above single structure cannot explain the characteristics of the carbonate ion. It is, thus, said that resonance exists in this ion and there is one hybrid form which can provide the exact explanation but its exact structure cannot be written on paper. Carbonate ion is actually a resonance hybrid of the following forms :     The resonance hybrid can be best represented as :

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