What determines entropy?

[sera2018]

I know that

1. Entropy decreases from Gas > Liquid > Solid
2. 2 moles of a substance has more entropy than 1 mole
3. Greater molar mass/complexity means more entropy

Is there anything else I am missing?

This Khan Q said Na+ (aq) has greater entropy than PO3-4 (aq) because "Solvating ions in water creates more order since the water molecules have to organize itself around the ions. Ions tend to have negative standard entropies. In comparing the two ions, ions with a greater charge will tend to have more negative standard entropies."

But my TPR book said that "Particles in sol'n have more entropy than undissolved solids"

Is this question unique because it's talking specifically about water and not a general solution? I also don't really understand their explanation, it doesn't seem intuitive that solvating ions in water creates more order...

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[aldol16]

You're not comparing the same things here. It's saying that Na+, when sollvated, has more entropy than PO3-4. It's not comparing the solid forms of anything. It is true that particles in solutions have more entropy than those same particles in solid form. Because solids have less entropy than fluids or solutions. But the key to Na+ vs. PO3-4 is solvation shell. This is an important principle because it's the same reason why unfolded proteins cause negative entropy changes. In order to stabilize the charges on Na+ and PO3-4, the waters have to form an ordered shell around those charges - causing the entropy of the water to decrease. The larger the charge, the more waters needed for this shell.