Explain Like I'm in Class 12

Imagine you have 16 electrons to put into molecular orbitals for $O_{2}$. Lewis theory says you draw a double bond (O=O), which pairs all electrons. All paired = diamagnetic. Problem: when you dip liquid oxygen between poles of a strong magnet, it sticks! Paramagnetic substances stick to magnets. So Lewis/VBT is wrong.

Why does MOT get it right?

Think of MOs like floors in a building. The π*2p antibonding orbitals come as a PAIR of identical floors (degenerate). Hund's rule says: if you have 2 electrons and 2 identical floors, put one electron on each floor (parallel spins) rather than doubling up. $O_{2}$'s 16th and 15th electrons land in these two floors — one per floor, unpaired.

Two unpaired electrons = paramagnetic. Done.

Why does Lewis/VBT fail? Lewis theory doesn't know about the existence of separate, degenerate π*2p orbitals. It just draws "two shared pairs" in a double bond and moves on. It has no way to split the electrons into separate orbitals within the same bond.

The deeper principle: MOT is fundamentally quantum mechanical — it uses orbital wavefunctions that extend over the WHOLE molecule. Electrons "see" all the molecular orbitals, not just bonds between two atoms. This is why MOT can handle degenerate orbitals correctly (via Hund's rule) while VBT cannot.

Takeaway for NEET:

• $O_{2}$: BO = 2, paramagnetic (2 unpaired in π*2p) — this is the DEFINITIVE MOT success
• $B_{2}$: also paramagnetic (2 unpaired in degenerate π2p) — another MOT-only prediction
• $N_{2}$: diamagnetic (BO=3, all electrons paired)
• $F_{2}$: diamagnetic (BO=1, all electrons paired)