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Ch.8 - Basic Concepts of Chemical Bonding
Chapter 8, Problem 55

Predict the ordering, from shortest to longest, of the bond lengths in CO, CO2, and CO32- .

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Identify the types of bonds in each molecule or ion. CO has a triple bond, CO<sub>2</sub> has two double bonds between carbon and oxygen, and CO<sub>3</sub><sup>2-</sup> (carbonate ion) has resonance structures typically represented with one double bond and two single bonds between carbon and oxygen.
Recall that generally, triple bonds are shorter than double bonds, and double bonds are shorter than single bonds due to the increasing number of shared electrons pulling the bonded atoms closer together.
Consider the effect of resonance in CO<sub>3</sub><sup>2-</sup>. Resonance can cause the actual bond lengths to be an average of the different forms, potentially making the bonds in CO<sub>3</sub><sup>2-</sup> shorter than a typical single bond but not as short as a double bond.
Compare the bond types and the effects of resonance to predict the relative bond lengths. Since CO has a triple bond, it should have the shortest bond length. CO<sub>2</sub> with double bonds should have a longer bond length than CO but shorter than CO<sub>3</sub><sup>2-</sup>.
Order the molecules and ion from shortest to longest bond length based on the analysis: CO (shortest), CO<sub>2</sub>, CO<sub>3</sub><sup>2-</sup> (longest).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bond Length

Bond length is the distance between the nuclei of two bonded atoms. It is influenced by the type of bond (single, double, or triple) and the size of the atoms involved. Generally, shorter bonds correspond to stronger interactions between atoms, while longer bonds indicate weaker interactions.
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Bond Order

Bond order refers to the number of chemical bonds between a pair of atoms. It is calculated as the difference between the number of bonding and antibonding electrons divided by two. Higher bond orders typically result in shorter bond lengths due to increased electron density between the nuclei, leading to stronger attractions.
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Resonance Structures

Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. In molecules like CO3^2-, resonance indicates that the actual bond lengths are an average of the different structures. This delocalization can affect bond lengths, making them longer than expected for a single bond but shorter than for a double bond.
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