Caption: "Shown here is the thermal motion of a segment of protein alpha helix. Molecules have various internal vibrational and rotational degrees of freedom. This is because molecules are complex objects; they are a population of atoms that can move about within a molecule in different ways. This makes molecular gases distinct from the noble gases (helium (He,Z=2), neon (Ne,Z=10), argon (Ar,Z=18), krypton (Kr,Z=36), xenon (Xe,Z=54), radon (Rn,Z=86), and, possibly and only in principle, oganesson (Og,Z=118)), which are monatomic gases (which consist of individual atoms). Heat energy is stored in molecules's internal motions which gives them an internal temperature." (Somewhat edited.)

The thermal motion is quantitified by its microscopic kinetic energy and other things too.

Credit/Permission: © User:Greg L, 2006 (uploaded to Wikipedia by Frode (AKA User:Froko), 2007) / Creative Commons CC BY-SA 3.0.
Image link: Wikipedia: File:Thermally Agitated Molecule.gif.
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