Ch.11 - Chemical Bonding II: Molecular Shapes, VSEPR & MO Theory

Tro - Chemistry: A Molecular Approach 6th Edition

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Ch.11 - Chemical Bonding II: Molecular Shapes, VSEPR & MO Theory

Problem 80d

Chapter 11, Problem 80d

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the π_2p orbitals lie at higher energy than the σ_2p, draw MO energy diagrams and predict the bond order in a molecule or ion with each number of total valence electrons. Will the molecule or ion be diamagnetic or paramagnetic? d. 14

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Identify the second-row homonuclear diatomic molecule with 14 valence electrons. This corresponds to the molecule N2.

Draw the molecular orbital (MO) energy diagram for N2. For second-row diatomic molecules, the order of orbitals is: \( \sigma_{1s} \), \( \sigma^*_{1s} \), \( \sigma_{2s} \), \( \sigma^*_{2s} \), \( \sigma_{2p} \), \( \pi_{2p} \), \( \pi^*_{2p} \), \( \sigma^*_{2p} \).

Fill the molecular orbitals with the 14 valence electrons, starting from the lowest energy orbital and following the Pauli exclusion principle and Hund's rule.

Calculate the bond order using the formula: \( \text{Bond Order} = \frac{(\text{Number of electrons in bonding MOs} - \text{Number of electrons in antibonding MOs})}{2} \).

Determine if the molecule is diamagnetic or paramagnetic. A molecule is diamagnetic if all electrons are paired and paramagnetic if there are unpaired electrons.

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Key Concepts

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

Molecular Orbital Theory

Molecular Orbital (MO) Theory describes how atomic orbitals combine to form molecular orbitals that can be occupied by electrons. In diatomic molecules, these MOs can be bonding or antibonding, influencing the molecule's stability and properties. The energy levels of these MOs are determined by the types of atomic orbitals involved and their relative energies, which is crucial for predicting molecular behavior.

Bond Order

Bond order is a measure of the number of chemical bonds between a pair of atoms, 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 indicates a double bond.

Magnetism in Molecules

The magnetic properties of a molecule, whether it is diamagnetic or paramagnetic, depend on the presence of unpaired electrons in its molecular orbitals. Diamagnetic molecules have all electrons paired and are not attracted to a magnetic field, while paramagnetic molecules contain unpaired electrons and are attracted to magnetic fields. This property is essential for understanding the reactivity and stability of molecules.

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