The molecular orbital picture of H₂ can be represented by the following diagram. Label σ and σ* on the diagram—that is, which is (a) and which is (b)? Which is lower in energy? Why?
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Verified step by step guidance

Step 1: Observe the molecular orbital diagram provided. The diagram shows two molecular orbitals formed from the combination of two atomic 1s orbitals. The lower orbital (a) is labeled as bonding, and the higher orbital (b) is labeled as antibonding.

Step 2: Label the bonding molecular orbital as σ. This orbital is formed by the constructive interference of the atomic orbitals, leading to increased electron density between the nuclei. It is lower in energy because it stabilizes the molecule by reducing repulsion between the nuclei.

Step 3: Label the antibonding molecular orbital as σ*. This orbital is formed by the destructive interference of the atomic orbitals, leading to a node (region of zero electron density) between the nuclei. It is higher in energy because it destabilizes the molecule by increasing repulsion between the nuclei.

Step 4: Explain why the bonding orbital (σ) is lower in energy. The constructive overlap of atomic orbitals in the bonding orbital allows electrons to be shared between the nuclei, creating a stabilizing effect. This reduces the overall energy of the system.

Step 5: Explain why the antibonding orbital (σ*) is higher in energy. The destructive overlap creates a node, which reduces electron density between the nuclei and increases repulsion. This destabilizing effect raises the energy of the system.

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Key Concepts

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

Molecular Orbitals

Molecular orbitals (MOs) are formed by the linear combination of atomic orbitals (LCAO) when atoms bond together. In diatomic molecules like H₂, the bonding molecular orbital (σ) is lower in energy and is formed from the constructive interference of atomic orbitals, while the antibonding molecular orbital (σ*) is higher in energy due to destructive interference. Understanding these orbitals is crucial for predicting molecular stability and reactivity.

Bonding vs. Antibonding Orbitals

Bonding orbitals, such as σ, stabilize the molecule by allowing electron density between the nuclei, which lowers the energy of the system. In contrast, antibonding orbitals, like σ*, have a node between the nuclei and increase the energy of the molecule when occupied. The presence of electrons in these orbitals influences the bond order and overall stability of the molecule.

Energy Levels in Molecular Orbitals

In molecular orbital theory, the energy levels of MOs are determined by the extent of overlap between atomic orbitals. The σ orbital is lower in energy than the σ* orbital because it results from constructive overlap, which stabilizes the molecule. Conversely, the σ* orbital, resulting from destructive overlap, is higher in energy, making it less stable. This energy difference is fundamental in understanding molecular bonding and the behavior of electrons in molecules.

The molecular orbital picture of H2 can be represented by the following diagram. Label σ and σ* on the diagram—that is, which is (a) and which is (b)? Which is lower in energy? Why?<IMAGE>