Ch.8 - Basic Concepts of Chemical Bonding

Problem 56

Chapter 8, Problem 56

Based on Lewis structures, predict the ordering, from shortest to longest, of N¬O bond lengths in NO+, NO2-, and NO3-.

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Determine the Lewis structure for each species: NO^+, NO_2^-, and NO_3^-.

Calculate the formal charge for each atom in the structures to ensure the most stable Lewis structure is used.

Identify the type of bonds present in each species: single, double, or resonance structures.

Understand that bond order is inversely related to bond length; higher bond order means shorter bond length.

Compare the bond orders: NO^+ has a bond order of 3, NO_2^- has a bond order of 1.5 (due to resonance), and NO_3^- has a bond order of 1.33 (due to resonance).

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Key Concepts

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

Lewis Structures

Lewis structures are diagrams that represent the bonding between atoms in a molecule and the lone pairs of electrons that may exist. They help visualize the arrangement of electrons and predict molecular geometry, which is crucial for understanding bond lengths. In the context of the question, drawing the Lewis structures for NO+, NO2-, and NO3- will reveal the number of bonds and electron pairs, influencing the bond lengths.

Bond Order

Bond order is a concept that indicates 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 generally correlate with shorter bond lengths due to increased electron density between the nuclei, which pulls them closer together. Understanding bond order is essential for predicting the relative lengths of N-O bonds in the given species.

Resonance Structures

Resonance structures are different ways of drawing the same molecule that show the delocalization of electrons. In molecules like NO2- and NO3-, resonance contributes to the stability and bond characteristics of the molecule. The presence of resonance can lead to bond lengths that are intermediate between single and double bonds, affecting the overall bond length in the N-O bonds. Recognizing resonance is key to accurately predicting bond lengths in the given compounds.

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Resonance Structures

Related Practice

Textbook Question

Consider the formate ion, HCO₂^-, which is the anion formed when formic acid loses an H⁺ ion. The H and the two O atoms are bonded to the central C atom. (b) Are resonance structures needed to describe the structure?

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Textbook Question

Consider the formate ion, HCO₂^-, which is the anion formed when formic acid loses an H⁺ ion. The H and the two O atoms are bonded to the central C atom. (c) Would you predict that the C—O bond lengths in the formate ion would be longer or shorter relative to those in CO₂?

Textbook Question

Predict the ordering, from shortest to longest, of the bond lengths in CO, CO₂, and CO₃^2- .

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Open Question

True or false: (a) The C¬C bonds in benzene are all the same length and correspond to typical single C¬C bond lengths. (b) The C¬C bond in acetylene, HC≡CH, is longer than the average C¬C bond length in benzene.

Textbook Question

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:(a) Draw all of the resonance structures of naphthalene. How many are there?

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Textbook Question

Mothballs are composed of naphthalene, C₁₀H₈, a molecule that consists of two six-membered rings of carbon fused along an edge, as shown in this incomplete Lewis structure:

(b) Do you expect the C—C bond lengths in the molecule to be similar to those of C—C single bonds, C ═ C double bonds, or intermediate between C—C single and C ═ C double bonds?

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