Bonding vs. Antibonding MOs: Key Differences Explained
Bonding MOs form when atomic orbitals overlap constructively, lowering energy and holding atoms together. Antibonding MOs arise from destructive overlap, raising energy and pushing atoms apart; the asterisk (*) labels them.
Students picture electrons as “glue” and forget glue can also repel. In practice, a stable O₂ molecule owes its existence to more Bonding MOs, yet teachers still struggle to explain why oxygen isn’t instantly torn apart by its own Antibonding MOs.
Key Differences
Bonding MOs increase electron density between nuclei, lower energy, and stabilize molecules. Antibonding MOs create a node between nuclei, increase energy, and weaken or break bonds.
Which One Should You Choose?
You don’t pick one; every molecule contains both. To predict stability, count electrons: fill Bonding MOs first; if Antibonding MOs end up occupied, the bond weakens or the molecule may not form.
Examples and Daily Life
N₂ is inert because its eight bonding electrons outweigh its two antibonding electrons. Meanwhile, hydrogen’s H₂⁺ ion exists briefly because only one electron occupies a Bonding MO, and none sit in the Antibonding counterpart.
Why does O₂ have unpaired electrons?
Its π* Antibonding MOs hold two electrons with parallel spins, making O₂ paramagnetic.
Can a molecule have zero Bonding MOs?
No; electrons must occupy at least one Bonding MO to hold nuclei together and form a molecule.