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Ch.10 - Chemical Bonding II: Molecular Shapes & Valence Bond Theory
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831Non è quello che usi tu?Cambia libro di testo
Capitolo 10, Problema 72

Draw an MO energy diagram and predict the bond order of Li2+ and Li2-. Do you expect these molecules to exist in the gas phase?

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Start by identifying the atomic orbitals involved in the formation of molecular orbitals for lithium (Li). Each Li atom has electrons in the 1s and 2s orbitals.
Construct the molecular orbital (MO) diagram for Li2. The 1s orbitals form the sigma (σ) 1s bonding and sigma star (σ*) 1s antibonding orbitals, while the 2s orbitals form the sigma (σ) 2s bonding and sigma star (σ*) 2s antibonding orbitals.
For Li2+, remove one electron from the highest occupied molecular orbital (HOMO) of Li2. For Li2-, add one electron to the lowest unoccupied molecular orbital (LUMO) of Li2.
Calculate the bond order for each species using the formula: Bond Order = (Number of electrons in bonding MOs - Number of electrons in antibonding MOs) / 2.
Discuss the stability of Li2+ and Li2- in the gas phase based on their bond orders. Generally, a positive bond order suggests that the molecule can exist, while a bond order of zero or negative suggests instability.

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Molecular Orbital Theory

Molecular Orbital (MO) Theory describes the behavior of electrons in molecules by combining atomic orbitals to form molecular orbitals. These orbitals can be bonding, antibonding, or non-bonding, and their energy levels determine the stability and reactivity of the molecule. Understanding MO theory is essential for predicting bond order and the existence of molecules in the gas phase.
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Molecular Orbital Theory

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 Li2+ and Li2-, calculating the bond order helps predict their stability and likelihood of existing in the gas phase.
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Average Bond Order

Stability of Molecules in the Gas Phase

The stability of molecules in the gas phase is influenced by their bond order and the energy of their molecular orbitals. Molecules with a positive bond order are generally stable and can exist in the gas phase, while those with a bond order of zero or negative are less likely to be stable. Evaluating the bond order of Li2+ and Li2- will provide insight into their potential existence as gaseous species.
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Phase Changes in Diagrams
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