Explain the difference between the \(\sigma\) and \(\pi\) MOs for homonuclear diatomic molecules. How are bonding and antibonding orbitals different? Why are there two \(\pi\) MOs and one \(\sigma\) MO? Why are the \(\pi\) MOs degenerate?

Short Answer

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In homonuclear diatomic molecules, σ orbitals form when atomic orbitals overlap along the internuclear axis, leading to greater electron density between the nuclei and cylindrical symmetry. π orbitals form when atomic orbitals overlap above and below, or in front and behind the internuclear axis, creating a nodal plane and concentrated electron density. Bonding orbitals arise from constructive interference of atomic orbitals and have lower energy, while antibonding orbitals arise from destructive interference and have higher energy. The two π MOs and one σ MO occur due to the combination of s- and p-orbitals in molecular orbital formation. Finally, π MOs are degenerate because they have the same energy level, resulting from their similar electron density distribution and electrostatic interactions.

Step by step solution

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1. Difference between σ and π MOs for homonuclear diatomic molecules

: In homonuclear diatomic molecules, atomic orbitals from two identical atoms combine to form molecular orbitals. These molecular orbitals can be classified into two types: Sigma (σ) molecular orbitals and Pi (π) molecular orbitals. Sigma (σ) molecular orbitals form when atomic orbitals overlap along the internuclear axis, leading to a greater electron density between the two nuclei. Due to this overlapping along the internuclear axis, σ orbitals have cylindrical symmetry around the internuclear axis. Pi (π) molecular orbitals, on the other hand, form when atomic orbitals overlap above and below, or in front and behind the internuclear axis. In this case, the electron density is concentrated above and below (or in front and behind) the internuclear axis, leading to a nodal plane containing the internuclear axis.
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2. Difference between bonding and antibonding orbitals

: When atomic orbitals combine to form molecular orbitals, two types of interactions can occur: Bonding and antibonding. Bonding orbitals result from the constructive interference of atomic orbitals, leading to an increased electron density between the nuclei. This increased electron density provides a stabilizing effect and, as a result, the energy of the bonding orbital is lower than the atomic orbitals from which it forms. Antibonding orbitals arise from the destructive interference of the atomic orbitals, leading to a decreased electron density between the nuclei with a nodal plane along the internuclear axis. This decreased electron density creates a destabilizing effect, and the energy of the antibonding orbital is higher than the atomic orbitals from which it forms.
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3. Reason behind having two π MOs and one σ MO

: This phenomenon occurs due to the nature of atomic orbitals that are involved in the molecular orbital formation. When an s-orbital combines with a nearby p-orbital along the internuclear axis, a σ orbital is formed. However, when the s-orbital combines with the other two p-orbitals that are perpendicular to the internuclear axis, two π orbitals are formed. Since there are two p-orbitals perpendicular to the internuclear axis and only one along the internuclear axis, we end up with two π MOs and one σ MO.
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4. Reason behind π MOs being degenerate

: Degenerate orbitals are orbitals that have the same energy level. In the case of π MOs, the two orbitals formed by the overlap of the two p-orbitals perpendicular to the internuclear axis are energetically equivalent. They have the same energy because their electron densities are distributed similarly around the internuclear axis, and as a result, they are affected equally by the electrostatic interactions between the electrons and the nuclei. This leads to π MOs being degenerate, meaning they have the same energy level.

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Most popular questions from this chapter

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