Drag the curve to pull the bond. Let go and it springs back to Rₑ.
An electron in an atom is a standing wave, its atomic orbital. When two atoms approach, their waves overlap and add. The result is a molecular orbital ψ that belongs to the whole molecule.
Bonding orbitals combine in phase and pile density between the nuclei. Antibonding orbitals (marked *) combine out of phase: a node cuts the bond. Bond order is half the difference between bonding and antibonding electrons.
Bond length is set by the molecule. Rₑ is the bottom of the energy well. Pull the bond is a what-if: stretch it and the bonding/antibonding split collapses toward the free atoms. Let go and it springs back and rings like a real vibration.
Resonance. Some molecules can't be drawn with a single Lewis structure. Benzene's two Kekulé structures are not two molecules that flip back and forth. The real molecule is their hybrid, and the delocalised π orbitals show it directly.
SMILES builds any small molecule (H B C N O F P S Cl, up to 64 atoms). Its 3D shape comes from VSEPR plus a small force field, and its orbitals from extended Hückel theory. Reaction lab follows one orbital along a reaction path as reactant orbitals mix into new bonds.
Gallery orbitals are qualitative LCAO (Hückel for benzene) with photoelectron energies. SMILES and reaction orbitals are extended Hückel (Hoffmann parameters) over valence Slater orbitals. Reaction geometries are interpolated along a constructed path. The energy profiles are schematic, drawn from literature Eₐ and ΔH.