Define one Atomic Mass Unit (a.m.u.)
According to Dalton, each element had a characteristic mass called atomic mass
It is denoted by amu (atomic mass unit) or simply u .
The SI unit of atomic mass is u (unified mass)
One atomic mass unit (1u) is a mass unit equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12 isotope.
1u = 1/12th mass of an Carbon-12 isotope = 1.67377 x 10 -27 kilogram