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Ch.9 - Molecular Geometry and Bonding Theories
Chapter 9, Problem 71f

Consider the H2+ ion. f. Which of the following statements about part (e) is correct: i. The light excites an electron from a bonding orbital to an antibonding orbital, ii. The bond order of the ion does not change when an electron is excited, or iii. In the excited state there are more bonding electrons than antibonding electrons?

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Understand the concept of molecular orbitals: In the H2+ ion, there is one electron that can occupy either a bonding or an antibonding molecular orbital.
Recall that when light excites an electron, it can move from a lower energy orbital (bonding) to a higher energy orbital (antibonding).
Evaluate statement i: If light excites an electron from a bonding orbital to an antibonding orbital, this statement is correct.
Evaluate statement ii: Bond order is calculated as (number of bonding electrons - number of antibonding electrons)/2. If an electron is excited from a bonding to an antibonding orbital, the bond order changes.
Evaluate statement iii: In the excited state, if an electron moves to an antibonding orbital, there will be equal numbers of bonding and antibonding electrons, not more bonding electrons.

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Key Concepts

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

Bonding and Antibonding Orbitals

In molecular orbital theory, electrons occupy molecular orbitals that can be classified as bonding or antibonding. Bonding orbitals are lower in energy and stabilize the molecule, while antibonding orbitals are higher in energy and can destabilize it. The transition of an electron from a bonding to an antibonding orbital can affect the stability and properties of the molecule.
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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. For example, a bond order of 1 indicates a single bond, while a bond order of 0 indicates no bond. Changes in electron configuration, such as exciting an electron to an antibonding orbital, can alter the bond order.
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Excited State

An excited state occurs when an electron absorbs energy and moves to a higher energy level, such as from a bonding to an antibonding orbital. In this state, the distribution of electrons can change, potentially affecting the bond order and stability of the molecule. Understanding the implications of an excited state is crucial for analyzing molecular behavior and reactivity.
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