How does molecular orbital theory explain the following...

How does molecular orbital theory explain the following observations? a. $\mathrm{H}_{2}$ is stable, whereas $\mathrm{He}_{2}$ is unstable. b. $\mathrm{B}_{2}$ and $\mathrm{O}_{2}$ are paramagnetic, whereas $\mathrm{C}_{2}, \mathrm{N}_{2},$ and $\mathrm{F}_{2}$ are diamagnetic. c. $\mathrm{N}_{2}$ has a very large bond energy associated with it. d. $\mathrm{NO}^{+}$ is more stable than $\mathrm{NO}^{-}$.

How does molecular orbital theory explain the following observations?
a. $\mathrm{H}_{2}$ is stable, whereas $\mathrm{He}_{2}$ is unstable.
b. $\mathrm{B}_{2}$ and $\mathrm{O}_{2}$ are paramagnetic, whereas $\mathrm{C}_{2}, \mathrm{N}_{2},$ and $\mathrm{F}_{2}$ are diamagnetic.
c. $\mathrm{N}_{2}$ has a very large bond energy associated with it.
d. $\mathrm{NO}^{+}$ is more stable than $\mathrm{NO}^{-}$.

Key Concepts

Energy Considerations and Bonding Stability

The overall stability of a molecule, as predicted by molecular orbital theory, is largely determined by the minimization of energy through the filling of bonding molecular orbitals. The arrangement of electrons into these orbitals results in a net stabilization if the bonding interactions outweigh the destabilizing effects of electrons in antibonding orbitals. This energy perspective explains variations in bond energies and the relative stabilities of different molecular species.

Electron Configuration in Molecular Orbitals

The electron configuration in molecular orbitals details how electrons fill the available bonding and antibonding orbitals in a molecule. This configuration determines the overall energy, bond order, and magnetic properties of the molecule. Variations in electron count, such as through ionization or electron addition, can lead to significant differences in molecular stability and reactivity by altering the occupancy of bonding versus antibonding orbitals.

Paramagnetism and Diamagnetism in Molecular Orbitals

Paramagnetism and diamagnetism are magnetic properties that arise from the presence or absence of unpaired electrons in molecular orbitals. In molecular orbital theory, molecules with unpaired electrons exhibit paramagnetic behavior because these electrons create magnetic dipoles, whereas molecules with all electrons paired are diamagnetic. This concept helps explain differences in the magnetic behavior of different molecules based on their electron configurations.

Bond Order

Bond order is a key concept derived from molecular orbital theory that indicates the strength and stability of a chemical bond. It is calculated by taking the difference between the number of electrons in bonding orbitals and those in antibonding orbitals, divided by two. A higher bond order corresponds to a stronger, more stable bond, while a bond order of zero implies that the molecule is unstable or non-existent.

Molecular Orbital Theory

Molecular Orbital Theory explains chemical bonding by combining atomic orbitals into molecular orbitals that extend over the entire molecule. These MOs can be classified as bonding, non-bonding, or antibonding based on their energy and electron density distribution. The theory provides a framework for understanding the stability, bond order, and magnetic properties of molecules, which are determined by the constructive or destructive interference of atomic orbitals when they combine.

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