Definitions for "Atomic mass"
Keywords:  amu, isotope, nuclide, protons, mass
Atomic mass is the correct name for the more commonly used term atomic weight The atomic mass of an element is the weighted aveverages of the masses (measured in atomic mass units) of all natural isotopes of the element. For example magnesium has 3 naturally occuring isotopes: Mg-24, 78.99 % Mg-25, 10.00 % Mg-26, 11.01 % Since Mg has an atomic number of 12, we know its nucleus has 12 protons. Thus, the atomic mass (atomic weight) of naturally occuring Mg is : M Mg = 0.7899 x (12 x 1.00728 amu + 12 x 1.00867 amu + 12 x 0.00055) + 0.1000 x (12 x 1.00728 amu + 13 x 1.00867 amu + 12 x 0.00055) + 0.1101 x (12 x 1.00728 amu + 14 x 1.00867 amu + 12 x 0.00055) - 0.215976 amu ( mass defect) = 24.30500 amu where 1.00728 amu = mass of a proton, 1.00867 amu = mass of a neutron, 0.00055 amu = mass of an electron and 0.215976 amu is mass equivalent of the energy released in the formation of the Mg nucleus from protons and neutrons (see Chemistry Review )
1. The sum of protons and neutrons in an atom's nucleus. 2. The combined mass of all the particles in a given atom.
the mass of a nucleus in atomic mass units (amu), based on a standard of 12.00000 for . Syn. atomic weight.