The sum of the number of neutrons and protons in the nucleus of an atom.<ref>Wile, Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000.</ref>
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The sum of the number of neutrons and protons in the nucleus of an atom.<ref>Wile, Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000.</ref> The atomic number is determined by the isotopic atomic weight.