[Physics] Doubt about states of matter

Question

What does exactly means "Small molecules may appear as solid, liquid, and gaseous phases without losing their molecular integrity"?,

I can't image how just a molecule can be a gas, liquid or solid. Or in fact the previous phrase refers to the state of aggregations of those small molecules?

My source is this article:

B Wunderlich, A classification of molecules, phases, and transitions as recognized by thermal analysis, Thermochimica Acta, Volumes 340–341, 14 December 1999, Pages 37-52

If you could suggest me a reference that extend the previous one to more modern states of matter like Bose-Einstein condensates, i would really appreciate it.

Answer 1

Yep, you're right, we can only talk about the phase of matter if we have a collection of molecules. It wouldn't make any sense to talk about a single molecule as being a solid, liquid, or gas because what matters is how the kinetic energy of the molecules (related to temperature) compares to the intermolecular bonding energy.

Solid: KE << BE

Liquid: KE < BE

Gas: KE >> BE

I think the context that this sentence appeared in adds further clarity, so I've included it below.

Here's the full paragraph along with Fig. 3:

The key distinction between the three classes of molecules is summarized in the bottom portion of Fig. 3. Small molecules may appear as solid, liquid, and gaseous phases without decomposition, while rigid macromolecules keep their bonding to nearest neighbors (their molecular integrity) only in the solid state. Due to internal rotation, flexible macromolecules can attain sufficient intramolecular disorder to melt (or dissolve) without breaking strong bonds. This property is at the root of many of the useful properties of polymers (plastic and rubber–elastic behavior in addition to high strength, light weight, and low melting temperatures). The three classes of molecules are thus very distinct in their phase behavior. No macromolecule can be evaporated thermally without decomposition. If one tries to place flexible macromolecules into the gas phase by evaporation of small solvent molecules from a dispersion of droplets of a solution with only one macromolecule per droplet, the macromolecules become microphase particles and collect at the bottom of the container [9].