CHEMISTRY COMMUNITY

Why does Oxygen have a low first ionization energy?

This is because of an electron being added to an already half full orbital in oxygen, which results in electron-electron repulsion,lowering the ionization energy.

Oxygen also has 4 electrons in the 2p orbital, yet it would rather have a half-full shell. Thus, it would be easier to remove the 4th electron.

what about the ionization energy of nitrogen? Is It greater than oxygen?

Victoria Otuya 4F wrote:what about the ionization energy of nitrogen? Is It greater than oxygen?

Yes because nitrogens subshells are completely half filled which is more stable than oxygen which has 1 pair and 2 lone electrons. The electron electron repulsion of oxygen’s orbital causes it to have a lower ionization energy than nitrogen

The first electron being removed from oxygen comes out of a full orbital. The electron-electron repulsion of the two e- decreases the magnitude of the force of the nucleus these electrons experience, decreasing the energy necessary to remove them from the atom.

Yeah this was a tricky question on the midterm but because of the extra (4th) electron in the 2p subshell, oxygen has a slightly lower IE than nitrogen.

Oxygen's electron configuration is 1s2 2s2 2p4. Since a p subshell houses three orbitals that can contain up to 6 electrons, a p subshell containing 3 electrons is considered half full with one electron in each orbital (as per Hund's Rule). Half full subshells can be somewhat desirable for atoms (although having full shells is preferable of course).

Victoria Otuya 4F wrote:what about the ionization energy of nitrogen? Is It greater than oxygen?

Nitrogen has a higher ionization energy, because it will take more energy to remove one electron from nitrogen than from oxygen. This is because nitrogen's 2p orbital is half filled, while oxygen's is partially (4/6) filled. Half-filled is more stable than partially filled, so it is easier to remove an electron from oxygen.