Talk:Nascent hydrogen

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"In chemistry, nascent hydrogen is non-ionised, monatomic hydrogen (H0) that exists transiently after the reduction of hydrogen ions."

I dont think that nascent hydrogen is real, sort of a folk-tale from the era when heterogeneous catalysis was less well understood. Indeed one can reduce diverse substrates with H+ plus metal, but is there really any evidence that free H forms even transiently? Instead, the so-called nascent hydrogen is just metal hydrides or H chemi-sorbed on the metal, and such ensembles are the reducing agents.

Vast amounts of atomic H exist in interstellar regions, but its high dilution precludes any chemistry.

So I recommend that this definition be changed into a disclaimer.Smokefoot 06:13, 29 January 2006 (UTC)

By that same token then there is no H+, ionic proton, because it's always absorbed to either and H₂O molecule giving an H₃O+, or sorbed into the dangling electrons on a metal surface, or sorbed to whatever it can find. We still talk about protons or hydrogen ions in acids. By the way a free proton is very rare, but it apparently does form in superacids such as HF/SbF₅ mixes, detectable by NMR, and even there you can argue that it's not free, but it's surrounded by an ionic cage of counterions that compensates for its positive charge. So no, there is no free atomic hydrogen just like there is no free proton, except in extreme cases, - I can think of hot plasma hydrogen gas quenched by liquid hydrogen that has a few neutral hydrogen atoms for a few nanoseconds during the quench - but even without these extreme cases of superacids or plasma, we still talk about pH or hydrogen ion concentration, or of atomic hydrogen at electrodes. That they are stuck to other things while waiting to react with something, because it's a lower energy state to wait like that, whether it's an H+ stuck to a water molecule, or an H0 stuck to a graphite/metal surface, that's besides the point, because it should be understood anyway that they are temporarily stuck to something. Sillybilly 09:06, 29 January 2006 (UTC)

Your comment about H+ being virtually unknown is very welcome indeed. The same can almost be said for F- and OH-. Nonetheless H+ in some form does exist, H9O4 + or where-ever one chooses to stop including the solvation shell. I am not disputing Hdot, I am disputing "nascent hydrogen" because of the implication of free (or even solvated) H. Yes, there are probably plasma situations where Hdot is involved, but the nascent hydrogen lore are not part of such discussion.Smokefoot 20:45, 29 January 2006 (UTC)

Also the idea of free Hdot in "nascent hydrogen" implies an outer sphere mechanism for reduction of protons, vs direct bonding of H+ to the reducing center.Smokefoot 23:54, 29 January 2006 (UTC)

Now that you say Hdot, a free radical hydrogen, I recall the free radical chain reactions: for instance hydrogen and chlorine gas mixture ignited by light, similar to how methane gets chlorinated. There are both chlorine atom radicals, and hydrogen atom radicals in that process: Cl₂+hʋ → 2 Cl*, Cl*+H₂ → HCL + H*, H*+Cl₂ → HCl + Cl*. In such cases the existence of atomic H* is fairly certain, unless, for some reason, the H* is nowhere near as stable as, say a CH₃* radical during methane chlorination, and instead it spends its time as a hydrogen bonded H₂Cl* resonance complex waiting for the available chlorine molecule to attack. There are definitely free radical chlorine atoms, and I'm guessing there are also non-resonance-complex free radical hydrogen atoms too. But when we speak of nascent hydrogen, we customarily mean a "just reduced" hydrogen at some conductor surface, such as graphite. I'm trying to picture a just reduced hydrogen generated someplace else than conductor surface, for instance an alkali metal dissolved in liquid ammonia that has a few drops of water added, or even just liquid ammonia itself reacting to form the amide. Such reactions are slow, as the need for an iron catalyst shows in the liquid ammonia case, hydrogen or any gas generation is extremely hard without some high energy sites available (such as high energy silica crystal defect sites with dangling unbonded electrons) to form a bubble, or a large surface area exchange surface that proceeds without bubble formation, such as hemoglobin bound carbon dioxide gets released in your lungs. But in such non-conductor-surface generated hydrogen atom cases how do you tell a nascent hydrogen? From its reducing potential? The alkali metal solution itself would have at least as much reducing potential, and it would be meaningless to talk about nascent hydrogen as a reducing agent, when you already have much more potent "nascent" alkali metals or high reducing potential organic molecules doing the same job even better. Unless you can come up with a sterically hindered molecule that's capable of being reduced, but can only sterically fit a hydrogen atom and not something larger, such as a sodium atom, but now this discussion is starting to be an overkill. Nascent hydrogen is a general term used for high reducing power, freshly generated hydrogen either by electrolysis or a metal/acid reaction, or a metal/base reaction (such as zinc/potassium hydroxide) that has to be used instantaneously before it turns into a low energy molecule that's not reactive without a catalyst such as nickel or palladium. There are limits to language itself, and if we probe too deeply into the meanings we may end up in a world without coherence. if nothing else, nascent hydrogen is still a concept, just like epicycles, phlogiston, caloric and luminiferous ether have been concepts, even if we later found out that they are incoherent with experimental reality and thus concepts that must be abandoned. Is the concept of nascent hydrogen so far off from reality and logically inconsistent with experiement to the point that it must be abandoned? Sillybilly 03:12, 30 January 2006 (UTC)

Thanks for your input sillybilly, requesting that you format and insert this into the current article. I don't think that it currently reflects a scientific viewpoint, more like borderline psuedoscience. 59.167.106.233 14:32, 1 January 2007 (UTC)