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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 80b

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–

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Identify the total number of electrons in the molecule NO⁻. Nitrogen (N) has 7 electrons, oxygen (O) has 8 electrons, and the negative charge adds 1 more electron, totaling 16 electrons.
Use the molecular orbital (MO) theory to distribute these 16 electrons in the molecular orbitals. For NO⁻, the order of filling is: \( \sigma_{1s}^2, \sigma^*_{1s}^2, \sigma_{2s}^2, \sigma^*_{2s}^2, \sigma_{2p_z}^2, \pi_{2p_x}^2 = \pi_{2p_y}^2, \pi^*_{2p_x}^2 = \pi^*_{2p_y}^1 \).
Calculate the bond order using the formula: \( \text{Bond Order} = \frac{1}{2} (\text{Number of bonding electrons} - \text{Number of antibonding electrons}) \).
Determine the magnetic behavior by checking for unpaired electrons. If there are unpaired electrons, the molecule is paramagnetic; if all electrons are paired, it is diamagnetic.
Conclude the bond order and magnetic behavior based on the calculations and observations from the previous steps.

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Key Concepts

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

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 indicates a stronger bond and greater stability of the molecule. For example, a bond order of 1 corresponds to a single bond, while a bond order of 2 corresponds to a double bond.
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Magnetic Behavior

Magnetic behavior in molecules is determined by the presence of unpaired electrons. Molecules with unpaired electrons exhibit paramagnetism, meaning they are attracted to magnetic fields, while those with all electrons paired are diamagnetic and are repelled by magnetic fields. Understanding the electron configuration and the arrangement of electrons in molecular orbitals is crucial for predicting a molecule's magnetic properties.
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Molecular Orbital Theory

Molecular Orbital Theory describes the behavior of electrons in molecules by considering the combination of atomic orbitals to form molecular orbitals. These orbitals can be bonding, antibonding, or non-bonding, and they help explain the stability, bond order, and magnetic properties of molecules. This theory is particularly useful for analyzing diatomic molecules, including both homonuclear and heteronuclear types.
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