Here’s a explanation of how Molecular Orbital Theory (MOT) explains the stability of diatomic molecules:
1. MOT Idea of Bonding
- In MOT, atomic orbitals combine to form molecular orbitals.
- There are bonding orbitals (help hold atoms together) and antibonding orbitals (try to push atoms apart).
- Stability comes from having more electrons in bonding orbitals than in antibonding orbitals.
2. Bond Order Determines Stability
- MOT uses bond order to explain stability:
- Positive bond order → more bonding electrons → molecule is stable.
- Zero bond order → bonding and antibonding electrons cancel → molecule is unstable and may not exist.
3. Electron Arrangement Matters
- The way electrons fill molecular orbitals affects stability:
- H₂, N₂, O₂ → have more electrons in bonding orbitals → they exist and are stable.
- He₂ → bonding and antibonding electrons are equal → bond order zero → molecule is unstable.
4. Energy Perspective
- Electrons in bonding orbitals lower the energy of the molecule.
- Electrons in antibonding orbitals raise the energy.
- A molecule is stable if the total energy is lower than the separate atoms.
In short:
MOT explains stability by counting electrons in bonding vs antibonding orbitals. More bonding electrons → more stability; more antibonding electrons → less stability.