Determination+of+Atomic+Mass

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Nowadays, scientists use 1/12 of the mass of a carbon 12 atom as the unified atomic mass unit, meaning that the isotope carbon 12's atomic mass would equal 12u. In order to find the atomic mass of elements of the periodic table, scientists would take the mass of one element and divide it by the mass of 1/12 of the mass of carbon 12. Theodore William Richards was given the 1914 Nobel Prize in chemistry for finding the atomic masses of 55 elements, using the same method described above. However, there were many attempts previous to using the "carbon 12" method to distribute a mass number to elements that did not work out so nicely.

Stanislao Cannizzaro attempted to measure the mass of elements by adopting the hydrogen atom as the mass standard, giving it a mass of 2. However, this attempt did not work out because with such a "small" element as the standard, there was too much experimental error in finding the mass of the other elements.

Another attempt made was by chemists who tried to assign masses on the fact that oxygen has the mass of 16. Their reasoning was 16 was the lowest number they could label oxygen as without hydrogen's mass being under 1. However, with the discovery of isotopes, and oxygen having many isotopes, there would be scientific error if oxygen, in general, would be used as the standard mass unit (in theory). This is mainly why chemists resolved to using 1/12 of the mass of carbon 12 as the unified atomic mass unit, for it is more specitic than just "oxygen".

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This Q & A directly relates to our learning of molar masses because in finding molar masses of elements, we use the atomic mass of the elements (which are retrieved from the periodic table). Also, we have done many other labs involving atomic mass. Therefore, this question, pertaining to atomic mass, directly relates to what we have been learning in Chem. class.

Follow-Up Questions
Have there been any questioning of the method used today to find the mass of elements? Were there any other attempt made at finding the mass of the elements? How did scientists determine that the atomic mass of carbon was 12//u//?