Chemistry deals with say 10^10 atoms or more (many types of molecules intermolecularly bounded together by dipole or disperson forces) so saying that quantum theory is the foundations of chemistry may be not be fully correct as quantum theory deals with countable number of atoms and only small molecules. Chemistry also grew out before the advent of quantum theory. Is it more correct to say that it is the 2nd law of thermodynamic which is at the foundations of chemistry? Chesmitry deals a lot with energy changes of molecules. i.e a molecule will change to a lower energy state. That use to puzzle me. How does a molecule 'know' there is a lower energy state in the first place? However I now realise it is really the 2nd law of thermodynamics and so the molecule dosen't 'know' but just does it 'naturally' according to this law.