One interesting counterexample to this is deuterium and water made from it. It is 11% denser than normal water, ice made from it sinks in normal water, it has a higher heat capacity, is more viscous and has a higher boiling point. It's also completely stable!
You can also drink it, though not a good idea to have more than a few sips due to the extra weight and different reactivity. You might feel dizzy if you drank a few glasses worth and it replaced the ordinary water in your inner ear.
Also, heavy water is typically slightly radioactive due to it usually containing tritiated water (T2O), though regular water can also contain that.
Apparently, swapping 20% of your cells' water with heavy water is survivable, but if you try this, don't blame me if you go sterile (cell mitosis will likely be affected).
Wow that's pretty interesting. I'm least surprised that deuterated chemistry is what's first mentioned, and I'm sure that there are some other good stuff in the category. I bet heavy gasoline (lol) has a lower octane number, for example.
