# Negative entropy value for F- (aq) and OH-(aq)?

1. Apr 28, 2010

### Null_

I'm currently studying thermodynamics, and while looking through the chart of $$\Delta$$ H$$\circ$$, S$$\circ$$, and $$\Delta$$ G$$\circ$$ values for 200+ substances. Out of these, I noticed that two (F- (aq) and OH- (aq) have a negative S$$\circ$$ value. How can a single ion have a negative entropy? I understand that irreversible rxns and rxns with more moles of product than reactants have a negative S$$\circ$$ value, but I am having trouble seeing a negative entropy value for an ion. And why just F- and OH-? What makes them special? Electronegative? (For F- at least..)?

Thanks.

2. Apr 28, 2010

### espen180

Your table most likely lists values for the standard formation enthalpies and entropies. A negative So value just means that going from F2(g) to F-(aq) involves a decrease of entropy.