Final answer:
Heavier atoms possess greater entropy and greater numbers of atoms increase the ways in which molecules can vibrate, leading to a larger number of possible microstates and higher entropy.
Step-by-step explanation:
The entropy of a substance is influenced by the structure of the particles (atoms or molecules) that comprise the substance.
For atomic substances, heavier atoms possess greater entropy due to the relation between particle's mass and the spacing of quantized translational energy levels. For molecules, greater numbers of atoms increase the ways in which the molecules can vibrate, leading to a larger number of possible microstates and higher entropy.