Comment by wnoise
7 years ago
Hydrogen would not be better. A helium atom is considerably smaller than a hydrogen molecule. Even if you could use atomic hydrogen, the helium atom's radius is significantly smaller due to the higher central charge that is only partially screened by the "other" electron.
Hydrogen binds with other hydrogen atoms to create H2 which is the only form of elemental hydrogen you’ll see outside of a lab helium is unique in that its singular atom is its own elemental molecule.
It's not unique in that. There are other single-atom molecules.
I don’t know anything about chemistry beyond high school (US public school) but presumably helium is the smallest single-atom molecule you’ll encounter if hydrogen is off the table.
TIL, which others? I thought other noble cases are dimers like Xenon also unlike helium I think all of them now found to form some compounds especially with the fluoride family.
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It's not unique. It's just the smallest.
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Im guessing it's the only one that's gaseous at room temperature and pressure?
Edit: Never mind, all the nobel gasses.
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Did it appear at any point that your parent doesn't know that with the really knowledgeable response he wrote? Why make a comment that doesn't add value?
Hydrogen would be better. Size isn't the most important factor. Gasses with low molecular mass have higher particle velocities. The velocity affects mixing, passage through holes (including filters), and the speed of sound. Hydrogen is about 2 AMU, 1 for each atom, while helium is about 4 AMU.
You can find the formulas in a typical college chemistry textbook.
If "hydrogen would be better", I guarantee companies that make highly-sensitive cryostats (like companies that manufacture MRIs) would do it.
They don't - even knowing He is more expensive that H, because helium is better at leak testing than hydrogen is