Can the idea of entropy be extended to orbitals?

The forward reaction for: $\ce{HF<->H^+ +F^-}$ is entropically favourable; but energetically unfavorable: as there is too much electron density for $\ce{F^-}$ ion to cope up. That's a reason why $\ce{HF}$ is a weaker than $\ce{HI, HCl}$ etc.

But, can there be another explanation for weak acidity of $\ce{HF}$?

How about we introduce the idea of entropy to orbitals. Let me explain, in $\ce{HF}$ the elctron is in a molecular orbital of greater region than in $\ce{F^-}$. So, the valence electron pair is in an entropically more favorable state in $\ce{HF}$ than in $\ce{F^-}$: where it is contained in little space. That's why, $\ce{HF}$ is more favorable than separated $\ce{H^+}$ and $\ce{F^+}$.

Maybe, for other hydracids of same kind eg. $\ce{HI, HCl}$ this effect isn't so important. That's why they are stronger acids.

The reason why a gas particle in a large volume has a large entropy is not because it has a lot of space to move around per se. A better explanation is that for a given energy, there are many accessible translational states (these states can be derived from the particle in a box model). If we assume that all of these translational states are equally likely to be populated, then the number of possible microstates for the system, $W$, is large and hence $S = k \ln W$ is large.