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Pallabi Mishra Grade: 12
        Earlier,the definition of one atomic mass unit was that it was equal to the mass of one Hydrogen atom. Later, it was changed to one-eighthn of an Oxygen atom. Yet, presently, it is that it is equal to one-twelth of the mass of one Carbon atom. What is the reason of these changes in definitions?
8 years ago

Answers : (1)

879 Points

Dear pallabhi,

The unified atomic mass unit replaced the atomic mass unit (chemical scale) and the atomic mass unit (physical scale), both having the symbol amu.  The amu (physical scale) was one-sixteenth of the mass of an atom of oxygen-16.  The amu (chemical scale) was one-sixteenth of the average mass of oxygen atoms as found in nature.

1 u = 1.000 317 9 amu (physical scale) = 1.000 043 amu (chemical scale)

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Sagar Singh

B.Tech, IIT Delhi

7 years ago
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