What do the numbers mean on the Periodic Table?
The numbers on the Periodic Table represent the atomic number and the atomic mass. The atomic number, located at the top, tells you how many protons are in an atom's nucleus. The atomic mass, usually shown at the bottom, is the weighted average mass of an atom's isotopes.
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On the Periodic Table, the atomic number (the smaller number) shows the number of protons in an element. The atomic mass (the bigger, sometimes decimal number) is the average mass of all the isotopes of the element.
Atomic number = protons. Atomic mass = average mass of isotopes. Easy peasy!
The little number up top is the atomic number, which is the number of protons. The bigger number at the bottom is the atomic mass.
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