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Atomic Mass and Atomic Mass Number (Quick Review)

Chemistry Quick Review of Atomic Data

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Atomic mass and mass number are listed on the periodic table.

Atomic mass and mass number are listed on the periodic table.

Tommy Flynn, Getty Images
Here's a quick review of what is meant by atomic mass and atomic mass number, as well as how actual particle mass relates to atomic number.

 

  • Z is used to signify the atomic number of an atom.

     

  • Z = # of protons of an atom

     

  • A is used to signify the atomic mass number (also known as atomic mass or atomic weight) of an atom.

     

  • A = # protons + # neutrons

     

  • A and Z are integer values.

     

  • When the actual mass of an atom is expressed in amu (atomic mass units) or g/mol then the value is close to A.

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