CHEM 121 glossary
Interference
What happens when two waves overlap: where crests meet crests they add (constructive interference); where crests meet troughs they cancel (destructive interference). Only waves interfere, so it is evidence of wave behaviour.
Example
In a two-slit experiment light forms alternating bright (constructive) and dark (destructive) bands. Orbitals interfere the same way: in-phase overlap builds a bonding MO, out-of-phase overlap an antibonding MO.