Meaning of negative entropy value

I was looking through the thermodynamic data chart at the back of my textbook and found that $\ce{S^{2-}\_{(aq)}, F^{-}\_{(aq)}, OH^{-}\_{(aq)}}$ all have negative entropy values. But according to the Boltzmann equation, $S=k\ln W$, so if $S<0$, $W<1$. But since $W$ is the number of microstates, how can $W$ be less than 1?


I read in some other places than this is based on the entropy of $\ce{H^+\_{(aq)}}$ being set to $0$, but why do we set this equal to $0$ and how does it follow Boltzmann's equation?


