Atomic Mass and Atomic Mass Number

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.