Skip to main content
Ch.10 - Chemical Bonding II: Molecular Shapes & Valence Bond Theory
Chapter 10, Problem 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?

Verified step by step guidance
1
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.

Verified Solution

Video duration:
0m:0s
This video solution was recommended by our tutors as helpful for the problem above.
Was this helpful?

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 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.
Recommended video:
Guided course
03:06
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.
Recommended video:
Guided course
00:36
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.
Recommended video:
Guided course
03:22
Phase Changes in Diagrams
Related Practice
Textbook Question

Consider the structure of the amino acid aspartic acid. Indicate the hybridization about each interior atom.

1328
views
Textbook Question

Sketch the bonding molecular orbital that results from the linear combination of two 1s orbitals. Indicate the region where interference occurs and state the kind of interference (constructive or destructive).

1214
views
Textbook Question

Draw an MO energy diagram and predict the bond order of Be2+ and Be2- . Do you expect these molecules to exist in the gas phase?

3724
views
1
comments
Textbook Question

Sketch the bonding and antibonding molecular orbitals that result from linear combinations of the 2px atomic orbitals in a homonuclear diatomic molecule. (The 2px orbitals are those whose lobes are oriented along the bonding axis.)

2059
views
1
rank
Textbook Question

Sketch the bonding and antibonding molecular orbitals that result from linear combinations of the 2pz atomic orbitals in a homonuclear diatomic molecule. (The 2pz orbitals are those whose lobes are oriented perpendicular to the bonding axis.) How do these molecular orbitals differ from those obtained from linear combinations of the 2py atomic orbitals? (The 2py orbitals are also oriented perpendicular to the bonding axis, but also perpendicular to the 2pz orbitals.)

817
views
Textbook Question

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the π2p orbitals lie at lower energy than the σ2p, 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? a. 4 b. 6

332
views