On the basis of MOT, explain why the stability of N2 decreases on ionization but the inverse is true for O2.
The stability of N2 decreases upon ionization, while the stability of O2 actually increases. This can be explained on the basis of Molecular Orbital Theory (MOT), which describes the behavior of electrons in molecules.
MOT is based on the combination of atomic orbitals to form molecular orbitals. In the case of N2 and O2, both molecules have a total of 14 electrons to distribute among their molecular orbitals.
When N2 is ionized, one electron is removed to form the N2+ ion. Thus, the remaining 13 electrons need to be distributed in the molecular orbitals. N2 has a total of 10 bonding electrons and 4 antibonding electrons. Bonding orbitals stabilize the molecule, while antibonding orbitals destabilize it.
In N2, the bonding orbitals are fully occupied, providing strong stability. However, upon ionization, one of the bonding electrons is removed. This shifts the balance of electrons towards the antibonding orbitals, which results in less stabilization and decreased stability of N2. Therefore, the stability of N2 decreases upon ionization.
On the other hand, when O2 is ionized to form O2+, two electrons are removed, leaving behind 12 electrons to distribute. O2 has 12 bonding electrons and 2 antibonding electrons. Similar to N2, the bonding orbitals in O2 stabilize the molecule while the antibonding orbitals destabilize it.
However, upon ionization, the removal of two electrons from the already antibonding orbitals of O2 leaves only the bonding orbitals occupied. This causes a shift towards increased occupancy of the bonding orbitals, leading to enhanced stability. Therefore, the stability of O2 actually increases upon ionization.
In summary, the stability of N2 decreases upon ionization due to a shift towards more occupied antibonding orbitals, while the stability of O2 increases upon ionization because of a shift towards more occupied bonding orbitals.