Question 8.9: Constructing an MO Diagram for a First Row Diatomic Molecule...

Constructing an MO Diagram for a First Row Diatomic Molecule
Construct an MO diagram for the $He_{2}$ molecule. What is its bond order? Is this molecule likely to be stable?

STRATEGY
Count the total number of valence electrons in the $He_{2}$ molecule and fill orbitals in the MO diagram starting with the lowest energy. Calculate the bond order according to the equation in this section. Bond orders greater than zero represent stable species; the higher the bond order, the stronger the bond.

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The hypothetical $He_{2}$ molecule has 4 electrons, 2 of which occupy the lower-energy bonding orbital, and 2 of which occupy the higher-energy antibonding orbital. Since the decrease in energy for the 2 bonding electrons is counteracted by the increase in energy for the 2 antibonding electrons, the $He_{2}$ molecule has no net bonding energy and is not stable. The hypothetical $He_{2}$ molecule has 2 bonding and 2 antibonding electrons and a bond order of (2 – 2)/2 = 0, which accounts for the instability of $He_{2}$ .

تعليق توضيحي 2022-11-19 134137

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