The third law of thermodynamics states that the entropy of a perfect crystal at 0 $\mathrm{K}$ is zero. In Appendix $4, \mathrm{F}^{-}(a q), \mathrm{OH}^{-}(a q)$ and $\mathrm{S}^{2-}(a q)$ all have negative standard entropy values. How can $S^{\circ}$ values be less than zero?