Atomic mass unit |
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The kilogram is the MKS unit of mass. When measuring the mass of atoms and molecules with a mass spectrometer it is possible to compare masses to many significant figures (say 12) but it is not possible to determine the mass of a particular nucleus, in kilograms, to better than six significant figures. To simplify the recording of data (for instance the publication of the masses of all possible combinations of carbon, hydrogen, oxygen and nitrogen atoms with less than 40 atoms in total) the atomic mass unit is used instead of the kilogram. One atomic mass unit is defined as one twelfth of the mass of the carbon 12 nucleus. The atomic mass unit is approximately.... ... a little less than the mass of the isolated protons and neutrons that make up the carbon 12 nucleus. |