9. Which element was originally used to calculate atomic mass units (amus)?

Answer 1

options:
A. Hydrogen
B. Nitrogen
C. Carbon

Answer 2

i think a

Answer 3

H is correct way back in the dark ages. Then oxygen was the standard for many many many years but the main problem (and confusing problem) was that the physicists used one set of numbers for oxygen and chemists used another set. I seem to remember that the conversion factor was 1.00275 between the two but I may not remember that correctly. About 60 years ago (I think in the late 1960s) everyone got their act together and agreed to the standard world wide which is C-12 set at 12.00000.

Answer 4

so its carbon right now?

Answer 5

Yes, C12 is set at 12.0000 and is used world wide as the standard. It isn't likely to change anytime soon. If you're interested in the history, the old oxygen standard, the one that was different for physicists and chemists, was used for years and I grew up with that in the 40s, 50s etc until C-12 was adopted in the late 1960s I think. The difference was how the two groups did it. Chemists used O16, O17, O18 in their normal isotopic ratio and called that 16.0000. But the physicists used O16 ONLY and set that equal to 16.0000. It turns out that physicists, with their mass spectrometers, can determine isotopic ratios and atomic masses MUCH MORE accurately than chemists can. By using C-12 the old scale and the new scale are about the same so chemists didn't need to change our thinking that much and C was a good match for the physics people so everyone compromised. It's much easier to work all of the problems now. In the old days, for example, all of the mass defects for the H bomb, the A bomb, most of the laws of physics, etc, it was necessary to use the physics scale OR to use the chemical scale and convert in order to make the masses come out right.