samboct
Posts: 1817
Joined: 1/17/2007
Status: offline
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Oh, hell, I might as well play hookey for 5 minutes and jump in too.
A couple of nits with shallow (who gave a very nice explanation)
Water's really annoying in terms of isotopes, since the most commonly available isotope of water is D20 (deuterium replacing hydrogen- hydrogen, 1 proton, one electron atomic weight of 1, deuterium, one proton, one neutron, one electron, atomic weight of 2)- which has a molecular weight of 20. I don't remember if the bond angles in D2O (aka heavy water) are altered relative to H20 (pretty sure they are), but I know that due to the increased molecular weight- the boiling point is increased and there are some changes in other physical properties as well. Basically since you double the mass of the hydrogen attached to the oyxgen, a bunch of stuff changes pretty significantly. And there are some very slight changes in the chemistry or physical properties of isotopes, otherwise we wouldn't be able to separate them. (often done with freezing point for oxygen, or gas diffusion or centrifugation for heavier isotopes.) Since most other molecules don't have such a significant change in molecular weight when you play with an isotope, the chemistry doesn't change so much.
For all those folks who worry that the world is full of toxins trying to poison them. Nature actually did make us reasonably robust- and here's an experiment that showed it. Back in the 50s, the postulation was that D2O would be poisonous, because many of our enzymes do hydrogen abstraction-i.e. pulling a hydrogen off of something- and often this hydrogen would come off of water. If you replace hydrogen with deuterium in a lab, often the rates that these reactions occur also slows down- a lot- sometimes by over 25% IIRC, maybe more. (Hey, it's been decades since I looked at this stuff, give me a break.) So the idea that D2O would be toxic made a lot of sense and the Army, bless it's fatigue green heart, decided to spend a LOT of taxpayer money (D2O was very expensive back then, it's pretty cheap today) and began adding D20 to the water fed to some beagles. Well, they got up to about 40% D2O on the dog, and not much was happening except the poor beagle gained some weight (hey- D20 is heavier than H2O) but aside from that, the dog seemed pretty much OK. Didn't grow two more heads, still barked, probably still peed on the carpet- that kind of thing. So I suspect we're pretty tolerant as to what kind of isotopic H2O we drink, as long as it's not emitting anything nasty.
Termnator-The Greeks had the right idea. The basic definition of an atom is that it's indivisible (well, to a chemist that's true- we don't change the nucleus) and interchangeable. The problem with what you're suggesting is that there would have to be a way to tell one proton or electron apart from another to change the properties- and both the Greeks and scientists today would say- No way, Jose.
Seeks- you oughta check out some of the images they're getting from SEM (think it's SEM) today- you can really see the electron orbitals over a metal surface. Pretty wild if you ask me. So electron density may only be a probability cloud, but it can be imaged- and not just as a theoretical construct.
And oh yeah- I'm another one who thinks that the Nellis claims are just complete nonsense. Like the expression goes- "there's a sucker born every minute."
Sam
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RE: Chemists ? A question, even if you know a little bit - 
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