What is actual difference between atomic hydrogen and nascent hydrogen?

Jul 28, 2017

Nascent hydrogen is an old term, outdated even, postulated to describe a "species" of atomic hydrogen gas that was produced in situ (on site), to claim that it is a "highly reactive" version of ${\text{H}}_{2} \left(g\right)$ stored over a longer period of time.

(Really, it is just an overly-simplified explanation of why such "species" [which are not new to us] tend to be more reactive than bottled ones stored over time.)

$\text{Zn"(s) + "H"_2"SO"_4(aq) -> "ZnSO"_4(aq) + overbrace(2"H"(g))^"'Nascent Hydrogen'}$

This tends to be in the context of dissolving-metal reactions. Although I usually see this reaction forming ${\text{H}}_{2} \left(g\right)$, this process shown above is at around $4000 - {4500}^{\circ} \text{C}$, which promotes homolytic cleavage of ${\text{H}}_{2}$ into $2 \text{H}$.

(These days, we know that of course it's more reactive than ${\text{H}}_{2} \left(g\right)$... $\text{H} \cdot$ is a radical!)

Atomic hydrogen is more generalized, and is simply the $\text{H}$ atom, one proton plus one electron.

$\text{H"_2(g) + "436 kJ" -> 2"H} \left(g\right)$

This is just in general, and out of context of dissolving-metal reactions. I don't think we use the term "nascent hydrogen" anymore...