davidbarnes
Trainee Mȯderatȯr
Why was the atomic weight of a;ll elements changed from being compared to Hydrogen (to carbon I think?)?
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Atomic Weight Comparison (1 Viewer)
- Thread starter davidbarnes
- Start date
http://en.wikipedia.org/wiki/Atomic_weight
The relative isotopic mass is the relative mass of the isotope, scaled with carbon-12 as exactly 12.
Before the 1960s, this was expressed so that the oxygen-16 isotope received the atomic weight 16, however, the proportions of oxygen-17 and oxygen-18 present in natural oxygen, which were also used to calculate atomic mass led to two different tables of atomic mass.
Formerly chemists and physicists used two different atomic mass scales. The chemists used a scale such that the natural mixture of oxygen isotopes had an atomic mass 16, while the physicists assigned the same number 16 to the atomic mass of the most common oxygen isotope (containing eight protons and eight neutrons). The unified scale based on carbon-12, <sup>12</sup>C, met the physicists' need to base the scale on a pure isotope, while being numerically close to the old chemists' scale.
The term atomic weight is being phased out slowly and being replaced by relative atomic mass, in most current usage. The term standard atomic weight refers to the mean relative atomic mass of an element.
Hope that helps
The relative isotopic mass is the relative mass of the isotope, scaled with carbon-12 as exactly 12.
Before the 1960s, this was expressed so that the oxygen-16 isotope received the atomic weight 16, however, the proportions of oxygen-17 and oxygen-18 present in natural oxygen, which were also used to calculate atomic mass led to two different tables of atomic mass.
Formerly chemists and physicists used two different atomic mass scales. The chemists used a scale such that the natural mixture of oxygen isotopes had an atomic mass 16, while the physicists assigned the same number 16 to the atomic mass of the most common oxygen isotope (containing eight protons and eight neutrons). The unified scale based on carbon-12, <sup>12</sup>C, met the physicists' need to base the scale on a pure isotope, while being numerically close to the old chemists' scale.
The term atomic weight is being phased out slowly and being replaced by relative atomic mass, in most current usage. The term standard atomic weight refers to the mean relative atomic mass of an element.
Hope that helps