Lesson 10 of 12 · 8 min
Homonuclear diatomic molecules
NCERT § "Bonding in Some Homonuclear Diatomic Molecules"
The air above Riya's glass is about 78 % nitrogen and 21 % oxygen. Nitrogen will not burn and hardly reacts; oxygen feeds the flame on her stove. MO diagrams explain the difference in one number each.
The lesson in notes
In short
H₂: bond order 1, diamagnetic. He₂: bond order 0, so it is not stable.
Li₂: bond order 1, diamagnetic. B₂: bond order 1, paramagnetic because its two π2p electrons are unpaired.
C₂: bond order 2, diamagnetic, and both bonds are π bonds in the MO picture.
N₂: bond order 3, diamagnetic, with a very high bond enthalpy.
O₂: bond order 2 with two unpaired electrons in the π* orbitals, so it is paramagnetic, which the Lewis structure cannot explain.
Removing an antibonding electron raises bond order: O₂⁺ has 2.5; adding electrons lowers it: O₂⁻ has 1.5 and O₂²⁻ has 1.
F₂: bond order 1, diamagnetic. Ne₂: bond order 0, not formed.