Definition of Atomic Mass Unit

Atomic mass unit is a term a mass that is equal to 1/12th of the mass of the carbon atom C-12. The masses of the isotopes (same atomic number but different atomic masses) of the elements are expressed in accordance with a standard which in this case is carbon-12. Take an example of an atom of helium and sulfur which have masses of 4.0026 and 31.972 amu respectively.


The size of an individual atom is extremely small. Despite employing the modern techniques of spectroscopy, it is impossible to measure the mass of such microscopic entities. Hence, the atomic mass unit was introduced so that the atomic masses can be compared with the standard.

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