Use the MO model to determine which of the following has the...

Use the MO model to determine which of the following has the smallest ionization energy: $\mathrm{N}_{2}, \mathrm{O}_{2}, \mathrm{~N}_{2}^{2-}, \mathrm{N}_{2}^{-}, \mathrm{O}_{2}^{+} .$ Explain your
answer.

Key Concepts

Molecular Orbital Theory

This theory describes how atomic orbitals combine to form molecular orbitals, which are spread over the entire molecule. In the context of diatomic molecules, it explains the formation of bonding and antibonding orbitals, and how electrons distributed among these orbitals determine key properties such as bond order and magnetic behavior.

Ionization Energy

Ionization energy is the energy required to remove an electron from a molecule. It is influenced by the electron configuration, particularly the energy level and type of orbital from which the electron is removed. Lower ionization energies generally occur when electrons occupy higher-energy or antibonding orbitals, as these electrons are less tightly bound to the nucleus.

Electron Configuration in Molecules

The specific arrangement of electrons in the molecular orbitals—both bonding and antibonding—affects the overall stability and reactivity of a molecule. Electrons in antibonding orbitals reduce the effective bond order, making it easier to remove an electron and thereby lowering the ionization energy.

Antibonding Orbitals

Antibonding orbitals are higher in energy than bonding orbitals and are populated by electrons that work against bond formation. Electrons in these orbitals are less tightly held, which means that molecules or ions with a larger proportion of electrons in antibonding orbitals typically show lower ionization energies.

Effects of Charge on Molecular Energy

The addition or removal of electrons to form charged species changes the electron configuration and the occupancy of molecular orbitals. Negative charges often add electrons into antibonding orbitals, resulting in a decreased bond order and lower ionization energy, while positive charges remove electrons from these orbitals and can have the opposite effect.

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