[13ren]

Deuterated bonds can be up to 80 times stronger than those containing hydrogen.

That seems likely to alter chemical behaviour (as researchers found). I'm not a chemist, but it seems reasonable to consider compounds with such bonds as different compounds. Why should we think of carbon-12 and carbon-13 as variations of carbon, instead of distinct elements - if they have different chemical behaviour?

The blackbox testing tells us that 35% heavy water is lethal, but doesn't tell why. It's possible - and even likely - that it is the very bonds we wish to protect that become lethal if strengthened 80 times.

The final "heavy babies" grayed paragraph at the end is fascinating (in case you skipped it: babies have more carbon-13, and their mothers are unusually depleted with it around the time of birth.)

[yummyfajitas]

They are both variations of carbon because they have the same electronic structure, i.e. the configuration of electrons about C-12 and C-13 is identical (or similarly H-1 and H-2).

I'll make a bad analogy now.

The electronic structure is like a set of hooks attached to the atom. Hydrogen has 1 free hook, carbon 4, and these hooks form chemical bonds. Hydrogen and deuterium have the same set of hooks, as do C-13 and C-14. But deuterium is heavier than hydrogen, and this makes it harder to unhook it when it attaches to another atom, even if the set of hooks is identical.

[13ren]

Sorry, that was a suggestion phrased as a question (i.e. I know what isotopes are). I was suggesting a name that signifies operational properties rather than "the" definition of what it is. If heavy water became commonly available, this would undoubtedly occur.

It's like features vs. benefits, which I've been working with over a few weeks, to understand the need for my product, and the gaps left by existing offers in the marketplace. Quite possibly, I'm thinking too much in those terms :-)