Atomic Mass Unit (u): This is a convenient mass unit to use when dealing with the masses of atoms and nuclear particles Were the mass expressed in kilograms the values would be so tiny they would be difficult for students to deal with The unit is defined by taking the mass of one atom of carbon12 as being 12u This makes the mass of a proton and a neutron to be equal to 1u (when measured to the degree of accuracy needed for GCSE level) 1u = 1 661 x 10-27 kg 1kg = 6 020 x 1026 u (Note - Some text books use the abbreviation amu)
A unit of mass equal to 1/16-th the mass of the atom of oxygen of atomic mass number 16, meaning that there are 16 nucleons in the standard oxygen nucleus A nucleon is either a proton or a neutron In terms of energy (using E = mc^2) an AMU = 931 Mev = 1 49 X 10^(-3) ergs
Chemical: one-sixteenth of the mean mass of an oxygen atom Physical: one-twelfth of the mass of an atom of the most common isotope of carbon The atomic mass unit is approximately the mass of a hydrogen atom, 1 67 x 10^-27 kg