Question

For the first ionization energy for an N₂ molecule, what molecular orbital is the electron removed from?

a) σ2s
b) σ2s
c) π2px
d) π2py

Answer 1

The electron removed during the first ionization energy of an N₂ molecule comes from the π2py molecular orbital.

Step-by-step explanation:

For the first ionization energy for an N₂ molecule, the electron is removed from the highest occupied molecular orbital (HOMO), which is the π2py. In the molecular orbital theory, the ordering of energy levels varies across the period 2 homo-nuclear diatomic molecules.

For molecules to the left of N₂ in the periodic table, the σ2p molecular orbital is higher in energy than the π2px and π2py orbitals. Therefore, these π orbitals are filled before the σ2p. However, for molecules from O₂ and beyond, this order changes and the σ2p becomes lower in energy than the π orbitals.

Since an N₂ molecule is to the left of O₂, the electron removed during ionization would come from the π2py orbital, which is the last filled and therefore the HOMO.