An elementary reaction is the simplest type of chemical reaction that takes place in one single step.
- It shows exactly how molecules collide and react in that step.
- The number of molecules taking part in the step tells you its molecularity (one = unimolecular, two = bimolecular, three = termolecular).
- Unlike complex reactions, it does not break into smaller parts.
Think of it like one direct move in a game, instead of a whole series of moves.