Ch.9 - Molecular Geometry and Bonding Theories

Problem 81a

Chapter 9, Problem 81a

Determine the electron configurations for CN+, CN, and CN-. (a) Which species has the strongest C¬N bond?

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Identify the total number of electrons for each species: CN+, CN, and CN-. CN has 13 electrons (6 from C and 7 from N), CN+ has 12 electrons, and CN- has 14 electrons.

Write the electron configuration for each species using molecular orbital theory. For CN, fill the molecular orbitals in the order: \( \sigma_{1s}^2, \sigma^*_{1s}^2, \sigma_{2s}^2, \sigma^*_{2s}^2, \pi_{2p_x}^2 = \pi_{2p_y}^2, \sigma_{2p_z}^2 \).

Adjust the electron configuration for CN+ by removing one electron from the highest occupied molecular orbital (HOMO) of CN, and for CN- by adding one electron to the HOMO of CN.

Determine the bond order for each species using the formula: \( \text{Bond Order} = \frac{1}{2} (\text{Number of bonding electrons} - \text{Number of antibonding electrons}) \).

Compare the bond orders of CN+, CN, and CN- to determine which species has the strongest C-N bond. The species with the highest bond order will have the strongest bond.

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Key Concepts

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

Electron Configuration

Electron configuration describes the distribution of electrons in an atom or ion across various energy levels and orbitals. It is represented using a notation that indicates the number of electrons in each subshell, such as 1s² 2s² 2p⁶. Understanding electron configurations is crucial for predicting chemical behavior, including bond formation and stability.

Bond Order

Bond order is a measure of 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. A higher bond order typically indicates a stronger bond, as it reflects greater electron density between the nuclei of the bonded atoms.

Ionic and Covalent Character

Ionic and covalent character refers to the nature of the bond between atoms, influenced by their electronegativities. In a covalent bond, electrons are shared, while in an ionic bond, electrons are transferred. The balance of these characters affects bond strength; for example, a more covalent bond often results in a stronger interaction between atoms, impacting the overall stability of the molecule.

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Textbook Question

Using Figures 9.35 and 9.43 as guides, draw the molecular orbital electron configuration for (d) Ne22 +. In each case indicate whether the addition of an electron to the ion would increase or decrease the bond order of the species.

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Textbook Question

If we assume that the energy-level diagrams for homonuclear diatomic molecules shown in Figure 9.43 can be applied to heteronuclear diatomic molecules and ions, predict the bond order and magnetic behavior of (b) NO+.

Determine the electron configurations for CN+, CN, and CN-. (b) Which species, if any, has unpaired electrons?

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Textbook Question

(a) The nitric oxide molecule, NO, readily loses one electron to form the NO⁺ ion. Which of the following is the best explanation of why this happens: (i) Oxygen is more electronegative than nitrogen, (ii) The highest energy electron in NO lies in a π_2p* molecular orbital, or (iii) The π_2p* MO in NO is completely filled.

Textbook Question

(c) With what neutral homonuclear diatomic molecules are the NO⁺ and NO^- ions isoelectronic (same number of electrons)? With what neutral homonuclear diatomic molecule is the NO^- ion isoelectronic (same number of electrons)?

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