I know that entropy is a measure of molecular disorder of a system. But how come that two different molecules have two different entropy-values?

 

Example: The entropy of

Hydrogen H2(g) = 131 J/(K·mol);

Helium He(g) = 126 J/(K·mol);

Fluorine F2(g) = 203 J/(K·mol);

... and so on. (Standard values at 298K and 1atm)

 

For me it would seem that the only factors (at inducing "randomness") to take into consideration would be size and #atoms/bonds in the molecule, but I can't seem to pick a trend...

Anybody can help me here, I have some guesses myself....????

... hmm, nobody want to give it a shot?

Don't forget the randomness of the particles in the nucleus, as well as the randomness in the electrons.