What is the range of sizes for molecular systems? Molecular systems - are in a simple count systems made up of molecules. But almost every system, surrounding us are molecular than. Considering the molecular systems in terms of chemistry compels us, firstly, impose dimensional constraints on the molecular system (which?), molecular system could not be macroscopic (How big?), otherwise you'll have to talk about it as a solid body; secondly, energies for such systems are limited (&lt;1 eV); in third place we will be interested in properties of such system as whole, but not as sum of its parts properties.

So the main question is raised: What is the range of sizes for molecular systems?
Well apportioned, mixed, and cured epoxy glue is a single covalent molecule.  Single crystal white diamond is a single covalently-bonded molecule.  On the small end, a dihydrogen molecule, is 0.7414 Å (ortho or para, your choice to trim the decimal).  

The largest human chromosome is ~220 million base pairs, or about 1.5x10^11 g/mol.