The atomic weights of certain elements have been revised over time as our understanding of atomic structure and measurement techniques has advanced. These revisions are based on scientific discoveries and improved experimental methods rather than being changed solely for convenience's sake.
The concept of atomic weight originated with John Dalton's atomic theory in the early 19th century, where he assigned relative weights to different elements based on their combining ratios in chemical reactions. However, Dalton's atomic weights were not entirely accurate and required refinement.
In the late 19th century, Dmitri Mendeleev developed the periodic table, organizing elements based on their atomic weights and chemical properties. This helped identify inconsistencies and led to adjustments in atomic weights as more precise measurements became available.
One notable example is the case of hydrogen. Initially, hydrogen's atomic weight was determined to be 1, making it the lightest element. However, with the discovery of isotopes, it was found that there are multiple forms of hydrogen with different masses. The most abundant isotope, protium, was given an atomic weight of 1, while deuterium and tritium, the other isotopes, were assigned atomic weights of 2 and 3, respectively.
Other elements have also seen changes in their atomic weights as more accurate measurements were made. For instance, oxygen's atomic weight was revised from 16 to 15.9994 based on more precise measurements using mass spectrometry.
In summary, atomic weights have been adjusted over time to reflect more accurate measurements and a deeper understanding of atomic structure. These changes are driven by scientific advancements rather than convenience alone.