Therefore, oxygen molecule has 16 electrons. In the formation of molecular orbitals, the electrons in the inner shells are expressed as KK denoting (s1s)2 (s*1s)2.The remaining 12 electrons are filled in molecular orbitals.
fig 1.20 - Molecular orbital energy level diagram for O
2 molecule
The electronic configuration of the molecule is:
O
2: KK(
s2s)
2 (
s*2s)
2 (
s2p
z)
2 (
p2p
x)
2 (
p2p
y)
2 (
p*2p
x)
1 (
p*2p
y)
1
Thus oxygen molecule has two bonds (one
s and other
p). Further, in accordance with Hund's rule the last two electrons in
p*2p
x and
p*2p
y orbitals will remain unpaired. Therefore the molecule has paramagnetic character due to the presence of two unpaired electrons. These facts are in accordance with experimental observations. The bond dissociation energy in O
2 molecule has been found to be 495 kJ mol
-1 and bond length 121 pm.
It is clear from fig.1.20 that the electron will be lost from antibonding Molecular orbital i.e.,
(p*2px)2 (p*2py)2 (p*2px)1
molecule, therefore, the bond strength of
will be more than that of O
2 molecule and bond length of
will be less than that of O
2 molecule.
This ion is formed by the addition of one electron as:
According to fig.1.20, the electron will be added to either of the antibonding:
be larger O
2 molecule.
This ion is formed by the addition of two electrons to O
2 molecule.
The additional electrons enter the two half-filled
p-antibonding MOs.
will be larger than that O2 molecule.
