How were atomic masses determined before mass spectroscopy existed?

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Discussion Overview

The discussion centers on the historical methods used to determine atomic masses before the advent of mass spectroscopy. Participants explore the techniques employed by early scientists, including chemical reactions and measurements, as well as the challenges they faced in achieving accuracy.

Discussion Character

  • Historical, Conceptual clarification, Exploratory

Main Points Raised

  • Some participants mention that atomic masses were determined through extensive chemical reactions, weighing reactants and products, and measuring volumes to derive ratios.
  • One participant provides an example involving the decomposition of water into hydrogen and oxygen, noting the importance of considering the correct forms of the elements (e.g., H2 and O2) in the measurements.
  • Another participant reflects on the difficulties faced by early scientists in making accurate measurements without modern equipment, highlighting the impact of isotopes on their results.
  • There is a recognition of the significant effort required to achieve a reliable periodic table based on these early measurements.

Areas of Agreement / Disagreement

Participants generally agree on the historical context and methods used to determine atomic masses, but there is no consensus on specific details or the accuracy of those early measurements.

Contextual Notes

Limitations include the potential for errors due to isotopes affecting measurements and the dependence on the definitions of elements in different states during experiments.

Kavorka
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I remember a professor mentioning something about how scientists did this when we were discussing the history of the periodic table (they originally ordered it by atomic mass). I can't seem to find an answer online without digging through a lot of stuff...there was one article on this topic specifically but the link is dead.
 
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Beginning of this will give you an summary
http://library.thinkquest.org/C006439/atomic/index.htm

Bascically it was done by a lot and a lot of chemical reactions to fill in the spots -weighing reactants and products, measuring volumes.

For example, water can be broken down into its constituents, hydrogen and oxygen in gaseous phase. So weigh the products and measure the volumes, use Avogadro, and other rules, and compare the results to get a ratio. Do more experiments to get more ratios and pick one of the elements as a standard which was oxygen in the beginning on which all others were based. Note that for one reaction, such as water, one would have to consider if the products were actually H and O, H2 and O, h and O2, etc. Other experiments would lead to a consensus.
 
It is easy to forget just how hard they used to work at measuring things when they couldn't go down the road and buy a gizmo to do it. No wonder they got the initial stab at a periodic table wrong, when isotopes were messing with their measurements. A truly fantastic story, involving hundreds and hundreds of measurements, to reduce the errors.

The same approach gave them a highly accurate model of the Solar System, long before there were massive telescopes or satellites.
 
Kavorka said:
I remember a professor mentioning something about how scientists did this when we were discussing the history of the periodic table (they originally ordered it by atomic mass). I can't seem to find an answer online without digging through a lot of stuff...there was one article on this topic specifically but the link is dead.

If you are not prepared to do this at times, you will not get far in Science, young man!
 

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